Northeast Fisheries Science Center Reference Document 02-11
Status
of the Northeast U.S. Continental Shelf Ecosystem:
A Report of the Northeast Fisheries Science Center's
Ecosystem Status Working Group
by Jason S. Link1 and Jon K.T. Brodziak1, editors;
with contributions from (listed alphabetically): Jon K.T. Brodziak1,
David D. Dow1, Steven F. Edwards1, Mary C. Fabrizio2,
Michael J. Fogarty1, Devorah Hart1, Jack W. Jossi3,
Joseph Kane3, Kathy L. Lang1, Christopher M.
Legault1, Jason S. Link1, Sharon A. MacLean3,
David G. Mountain1, Julia Olson1, William J.
Overholtz1, Debra L. Palka1, and Tim D. Smith1
1 National Marine Fisheries Serv.,
166 Water St., Woods Hole, MA 02543
2 National Marine Fisheries Serv.,74 Magruder Rd., Highlands,
NJ 07732
3 National Marine Fisheries Serv., 28 Tarzwell Dr., Narragansett,
RI 02882
Print
publication date August 2002;
web version posted September 9,
2002
Citation: Link, J.S.; Brodziak, J.K.T., editors, and Brodziak, J.K.T.; Dow, D.D.; Edwards, S.F.; Fabrizio, M.C.; Fogarty,
M.J.; Hart, D.; Jossi, J.W.; Kane, J.; Lang, K.L.; Legault, C.M.; Link, J.S.; MacLean, S.A.; Mountain, D.G.;
Olson, J.; Overholtz, W.J.; Palka, D.L.; Smith, T.D., contributors. 2002. Status of the Northeast U.S.
Continental Shelf Ecosystem: a report of the Northeast Fisheries Science Center's Ecosystem Status Working
Group. Northeast Fish. Sci. Cent. Ref. Doc. 02-11; 245 p.
Download complete PDF/print version
Executive
Summary
We describe trends and conditions within the Northeastern
U.S. continental shelf ecosystem. Conceptual models of ecosystem processes
and working hypotheses about their interrelationships are identified.
While interpreting information on the status of various ecosystem attributes
is a complex process, we believe the documentation within this report
provides a useful first step towards implementing ecosystem-based fisheries
management (EBFM) within this ecosystem. The principal objective of
this report is to characterize the state of the northeastern continental
shelf ecosystem using a vast array of available data.
Most of the data in this report were collected by the Northeast
Fisheries Science Center (NEFSC). The NEFSC conducts long-term scientific
monitoring of trends in living marine resources, ranging from zooplankton
to fish to whales, and of abiotic conditions (e.g., physical oceanography),
within the Northeastern U.S. continental shelf ecosystem. The NEFSC
bottom trawl survey (BTS) has been conducted since the 1960s. The BTS
has used a single, standardized, depth-stratified random design to
measure the distribution, abundance, and size-, and age-compositions
of fish populations as well as collect oceanographic data during spring
and fall seasons. Fish stomachs have been sampled during BTSs since
the early-1970s to examine trophic ecology. Several other surveys (e.g.,
Marine Resources Monitoring, Assessment, and Prediction [MARMAP], Ecosystem
Monitoring [ECOMON]) were also initiated in the 1970s to provide information
on chlorophyll a levels, 14C primary production, zooplankton and ichthyoplankton
abundance, and inorganic nutrients along transects perpendicular to
the coastline. Data collected during these surveys were augmented with
data from the Ships of Opportunity Program (SOOP), which used continuous
plankton recorders aboard commercial vessels steaming from Boston,
MA to Cape Sable, NS, Canada and from New York City to Bermuda to measure
plankton and hydrographic variables. Other information was gathered
from resource surveys for sea scallops, surf clams, whales, benthos,
and special projects that have been conducted over the past four decades.
In addition to these fishery-independent survey data, the NEFSC has
collected fishery-dependent data from catch sampling at port, at-sea
observer sampling, fishery logbook reports, and commercial and recreational
fishery landings statistics since the 1960s. These fishery-dependent
data provide the basis for many of the socio-economic factors we examine.
Substantial changes occurred within this ecosystem during
the late-1970s to early-1980s when many abiotic, biotic, and human
metrics exhibited coincident increases or decreases. Potential mechanisms
for the observed changes are identified, with multiple working hypotheses
provided where appropriate. For example, there appears to have been
a shift in relative biomass between the demersal and pelagic fish communities,
as demersal abundance has declined and pelagic abundance increased.
Potential changes due to a shift from a cooler to a warmer temperature
phase and due to a shift from low to high fishing effort may also be
important.
These observations should provide the basis for future
process-oriented research or multivariate approaches to further examine
potential causal relationships between biotic, abiotic, and socioeconomic
variables. We conclude with a list of working hypotheses which, if
addressed, should help to quantify the status of this ecosystem for
EBFM.
II. Introduction
(Click here for PDF Version)
A. Why this topic?
Ecosystem-based fisheries management (EBFM) has generated a lot of
scientific interest in recent years (see Link 2002b for an overview).
Many factors have contributed to the recent focus on EBFM, including
conflict among stakeholders, conflict between legislative requirements,
ongoing debate over the most important processes in marine ecosystems,
and recognition of the limitations of single species management. The
relative effects of multi-species predator-prey interactions, intra-
and interspecific competition, and changing oceanographic conditions
are important scientific issues that could hinder the near-term application
of EBFM. These ongoing issues are certainly not novel (e.g., Baird 1873;
Lankester 1884; Lotka 1925; Volterra 1926). Further, while several approaches
to address broader considerations in a fisheries context were proposed
in the 1970s and 1980s (e.g., Steele 1974; Andersen and Ursin 1977; May
et al. 1979; Mercer 1982; Kerr and Ryder 1989; Daan and Sissenwine 1991),
many basic issues still remain unaddressed.
Recently, some progress has been made in defining terms for EBFM, providing
rationale for using a more holistic management approach, and in particular,
answering when, why, and how EBFM can be practically implemented in a
fisheries context (e.g., Larkin 1996; Jennings and Kaiser 1998; Hall
1999; ICES 2000; Link 2000; NMFS 2000; Link 2002a, 2002b; Brodziak and
Link 2002). To date, there are few empirical descriptions of fisheries
ecosystems (see, for example, AFSC; Livingston 1999, 2000). Yet the direct
implementation of broader ecosystem considerations has not become widespread
in fisheries management even though they have been advocated (NMFS 1999;
NRC 1999; ICES 2000) and even mandated in recent years (NOAA 1996). There
are no clear protocols for actually implementing EBFM and some questions
of feasibility and definition are still unaddressed. However, implementation
will be via iteration and sequential improvement. To this end, the Group
has focused on documenting the status of the northeast U.S. continental
shelf ecosystem as an essential first step to facilitate the development
of an operational approach to ecosystem-based fisheries management.
B. General background of the Working Group
The core of our Ecosystem Status Working Group (hereafter, the Group)
started out approximately in mid-1998 as a reading group for interested
staff from the NEFSC to keep abreast of current issues in fisheries science
and management. After reading and discussing and numerous literature
articles on the subject, including Steve Hall's (1999) book on the topic,
the Group realized that we could make a positive contribution towards
the implementation of ecosystem-based fisheries management. Since the
NEFSC has some of the world's premier time series of fisheries independent
data, on subjects ranging from species abundance to zooplankton biomass
to food habits to temperature, the Group thought it would be very useful
to assemble these data to document the current status and recent history
of the northeastern U.S. continental shelf ecosystem.
Our first objective was to assemble the diverse, multi-disciplinary
sets of time series that exist at the NEFSC in detail (Table
2.1). This document describes those abiotic, biotic and human metrics.
For a list of these metrics, see Table 2.1. Our
second objective was to compare these metrics. We compiled these diverse
datasets in common formats amenable for easy comparison. From this compilation,
we produced a set of simple, common, general observations. Our third
objective was to synthesize the information into a set of working hypotheses
that can serve as a basis for future detailed examinations.
C. New England fisheries: Case study for ecosystem-based
fisheries management
The substantial changes in New England fisheries over the past several
decades, and in particular groundfish fisheries, have been associated
with excessive fishing pressure (Serchuk
et al. 1994; Murawski
et al. 1997; Boreman et al. 1997; NEFSC 1998a; Fogarty and Murawski 1998).
The abundance of commercially desirable gadids (Atlantic cod, Gadus
morhua, and haddock, Melanogrammus aeglefinus) as well
as flatfish (yellowtail flounder, Limanda ferruginea, American
plaice, Hippoglossoides platessoides, and winter flounder, Pseudopleuronectes
americanus) has declined with a concurrent increase in the abundance
of elasmobranchs (spiny dogfish, Squalus acanthias, and skates, Raja spp.)
and small pelagic fishes. Changes
in the fish community structure began occurring in the 1950s and 1960s
with the arrival of distant water fleets and subsequent increase in fishing
pressure exerted on the major gadid and flatfish stocks. As a result
of the dramatic increase in landings (and presumably high discards),
the estimated total biomass of these stocks declined by at least 50%.
After the foreign fleets were displaced from the U.S. Exclusive Economic
Zone (EEZ), moderate increases in stock sizes were observed in the late-1970s
to early-1980s. Capacity and efficiency of the domestic fleet increased
during the 1980s, however, and this led to subsequent declines in groundfish
abundance. Groundfish abundance plummeted to historic lows in the 1990s,
although abundances of some stocks have increased in recent years under
restrictive fishery management measures. Yet some groundfish stocks,
such as cod, have remained at low abundance. Many
groundfish stocks on Georges Bank exhibited classic signs of overfishing
in recent decades, including declines in abundance, faster growth, earlier
age-at-maturity, and a truncated size structure (NEFSC 1998a, 1998b;
reviewed in Jennings and Kaiser 1998). However, much less in known about
the indirect and secondary effects of intense fishing pressure on the
fish community in this and most marine ecosystems (Hall 1999; ICES 2000).
Further, how fishing pressure affects other aspects of the northeast
U.S. continental shelf ecosystem are generally not known. In this context,
we hope to provide some insights on the issue of indirect effects, particularly
in the context of the fishing and environmental changes that have occurred
in this ecosystem.
D.
Spatial delineation of northeastern U.S. continental shelf ecosystem
We use ecosystem to refer
to the combination of physical processes and organisms existing within
the spatial range of the system, taken together as a whole. The spatial
range of the northeastern U.S. continental shelf ecosystem includes
the estuarine and oceanic waters to depths of approximately 200 m from
a southern boundary at Cape Hatteras, North Carolina to a northeastern
boundary at the beginning of the Scotian Shelf (<100 m depth) in
the northeastern Gulf of Maine through the Northeast Channel separating
Georges Bank from Browns Bank and the Scotian Shelf (Figure
2.1). It is also commonly referred to as the Northeast Large
Marine Ecosystem (LME; Sherman1991, Sherman et al. 1993). This ecosystem
is an open oceanic system that is part of the northwestern Atlantic
continental shelves province, which is a much larger oceanic region
consisting of continental shelf and slope water from Florida to the
Grand Banks of Newfoundland (Longhurst 1998). Within this ecosystem,
we define four subdivisions with distinct hydrography and biota: the
Mid-Atlantic Bight, Southern New England, Georges Bank, and the Gulf
of Maine-Bay of Fundy. We will provide metrics to describe system attributes
at several spatial scales, ranging from individual estuaries to subdivisions
to the entire northeastern U.S. continental shelf ecosystem.
E.
Temporal extent and resolution
Many of the metrics we examined
are derived from the NEFSCs spring and fall bottom trawl survey (Grosslein
1969; Azarovitz 1981; NEFC 1988). These extend back to 1968 and 1963,
respectively, and are maintained to the present time. Several other
time series (e.g., MARMAP, SOOP, food habits, vessel landings) are
available for the same time period. We present a suite of over 100
metrics, many of which span 25 - 40 years (Table 2.1).
Metrics with short time series have been included even though they
may represent only snapshots of particular system attributes, however,
most of the metrics provide information on annual or interannual time
scales. Although some data were available to examine seasonal contrasts,
we did not require this level of resolution to document the status
of the ecosystem.
F.
References
Andersen,
K.P., and Ursin, E.. 1977. A multispecies extension to the Beverton
and Holt theory, with accounts of phosphorus circulation and primary
production. Meddelelser fra Danmarks Fiskeri-og Havundersogelser N.S.,
7:319-435.
Azarovitz,
T.R. 1981. A brief historical review of the Woods Hole Laboratory trawl
survey time series. In: Bottom Trawl Surveys. Doubleday W.
G. and Rivard D. Canadian Special Publications in Fisheries and Aquatic
Sciences 58:62-67.
Baird, S.F. 1873. Report
on the condition of the sea fisheries of the south coast of New England
in 1871 and 1872. Report of the United States Fish Commission, Vol.
1. GPO, Washington, D.C.
Boreman, J., Nakashima,
B.S. Wilson, J.A., and Kendall, R.L. (Eds), 1997. Northwest Atlantic
groundfish, perspectives on a fishery collapse. American Fisheries
Society, Bethesda, MD.
Brodziak, J. and Link, J.
2002. Ecosystem Management: What is it and how can we do it? Bull.
Mar. Sci. 70(2):589-611.
Daan, N., and Sissenwine,
M.P. (eds). 1991. Multispecies models relevant to management of living
resources. ICES Marine Science Symposium 193.
Fogarty, M.J., Murawski,
S.A., 1998. Large scale disturbance and the structure of marine systems,
fishery impacts on Georges Bank. Ecol. Appl., 8(1):Supplement S6-S22.
Grosslein. M.D. 1969. Groundfish
survey program of BCF Woods Hole. Comm. Fish. Rev. 31(8-9):22-25.
Hall, S.J. 1999. The effects
of fishing on marine ecosystems and communities. Blackwell Science,
Oxford, England.
ICES (International Council
for the Exploration of the Sea). 2000. Ecosystem effects of fishing.
ICES Journal of Marine Science Volume 57, Number 3. 791 pp.
Jennings, S., Kaiser, M.J.
and Reynolds, J.D. 2001. Marine Fisheries Ecology. Blackwell Science,
Oxford, England.
Jennings, S. and Kaiser,
M.J. 1998. The effects of fishing on marine ecosystems. Advances in
Marine Biology 34:201-352.
Kerr, S.R. and Ryder, R.A.
1989. Current approaches to multispecies analysis of marine fisheries.
Canadian Journal of Fisheries and Aquatic Sciences 46:528-534.
Lankester, E.R. 1884. The
scientific results of the exhibition. Fisheries Exhibition Literature
4:405-42.
Larkin, P.A. 1996. Concepts
and issues in marine ecosystem management. Reviews in Fish Biology
and Fisheries 6:139-164.
Link,
J. 2000. Fisheries management in an ecosystem context: what does this
mean, what do we want, and can we do it? Proceedings of the 6th National
Stock Assessment Workshop: Incorporating Ecosystem Considerations into
Stock Assessments and Management Advice. NOAA Tech. Memo. NMFS-F/SPO-46.
pp. 5-11.
Link, J.S. 2002a. Ecological
Considerations in Fisheries Management: When Does It Matter? Fisheries
27(4):10-17.
Link, J.S. 2002b. What Does
Ecosystem-Based Fisheries Management Mean? Fisheries 27(4):18-21.
Livingston, P.A. (ed.).
1999. Ecosystem Considerations for 2000. Appendix: Stock Assessment
and Fishery Evaluation Report for the Groundfish Resources of the Eastern
Bering Sea, Aleutian Islands, and Gulf of Alaska. North Pacific Fishery
Management Council, 605 W. 4th Ave, Suite 306, Anchorage,
AK, 99501. 140 pp.
Livingston, P.A. (ed.).
2000. Ecosystem Considerations for 2001. Appendix: Stock Assessment
and Fishery Evaluation Report for the Groundfish Resources of the Eastern
Bering Sea, Aleutian Islands, and Gulf of Alaska. North Pacific Fishery
Management Council, 605 W. 4th Ave, Suite 306, Anchorage,
AK, 99501. 119 pp.
Longhurst, A. 1999. Ecological
geography of the sea. Academic Press, New York, 398 p.
Lotka, A.J. 1925. Elements
of physical biology. Williams and Wilkins, Baltimore, MD.
May, R.M., J.R. Beddington,
C.W. Clark, S.J. Holt, and R.M. Laws. 1979. Management of multispecies
fisheries. Science 205-267-277.
Mercer, M.C. 1982. Multispecies
approaches to fisheries management advice. Canadian Special Publication
in Fisheries and Aquatic Science 59.
Murawski,
S.A., Maguire, J.J., Mayo, R.K., Serchuk, F.M. 1997. Groundfish stocks
and the fishing industry. pp. 27-70, In: Boreman J., Nakashima
B.S. , Wilson J.A., Kendall R.L. (eds.) Northwest Atlantic groundfish:
perspectives on a fishery collapse. American Fisheries Society, Bethesda,
Maryland, USA.
Murawski, S.A. 2000. Definitions
of overfishing from an ecosystem perspective. Symposium proceedings
on the ecosystem effects of fishing, ICES Journal of Marine Science
57:649-658.
NEFC
(Northeast Fisheries Center). 1988. An evaluation of the bottom trawl
survey program of the Northeast Fisheries Science Center. NOAA Tech.
Memo. NMFS-F/NEC-52.
NEFSC, (Northeast Fisheries
Science Center) 1998a. Status of the Fishery Resources off the Northeastern
United States. NOAA Tech. Memo. NMFS-NE-115. 149 pp.
NEFSC. 1998b. 27th Northeast
Regional Stock Assessment Workshop. NEFSC Center Reference Document
98-15. 350 pp.
NRC (National Research Council).
1999. Sustaining Marine Fisheries. National Academy Press, Washington,
D.C.
NMFS (National Marine Fisheries
Service). 1999. Ecosystem-based fishery management. A report to Congress
by the Ecosystems Principles Advisory Panel. US Department of Commerce,
Silver Spring, MD.
NMFS. 2000. Proceedings
of the 6th National Stock Assessment Workshop: Incorporating
Ecosystem Considerations into Stock Assessments and Management Advice.
NOAA Tech. Memo. NMFS-F/SPO-46.
NOAA
(National Oceanic and Atmospheric Administration). 1996. Magnuson-Stevens
Fishery Management and Conservation Act amended through 11 October
1996. NOAA Technical Memorandum NMFS-F/SPO-23.
Serchuk, F.M., Grosslein,
M.D., Lough, R.G., Mountain, D.G., and O'Brien, L. 1994. Fishery and
environmental factors affecting trends and fluctuations in the Georges
Bank and Gulf of Maine Atlantic cod stocks: an overview. ICES Mar.
Sci. Symp. 198, 77-109.
Sherman, K. 1991. The large
marine ecosystem concept: research and management strategy for living
marine resources. Ecological Applications 1:349-360.
Sherman, K., Alexander,
L.M. and Gold, B.D. (eds). 1993.
Large marine ecosystems: stress, mitigation and sustainability. AAAS
Press, Washington, D.C.
Steele, J.H. 1974.
The structure of marine ecosystems. Blackwell Scientific Publ., Oxford,
U.K.
Volterra, V. 1926. Fluctuations
in the abundance of a species considered mathematically. Nature 118:558-560.
III. ABIOTIC METRICS
(Click here for PDF Version)
A. Geology, Chemistry
Geologic and chemical features significantly influence the physical
and biological components of this ecosystem. Although data on these factors
exists, few time series are available.
We do not include geological metrics in this report because the extant
data and expertise in this area reside with the United States Geological
Survey. From an ecosystem perspective, we need definitions of major geologic
regions, including the distributions of major sediment/bottom types,
and delineations of high/low energy areas in the ecosystem. Some information
on the marine geology of the region is summarized in Backus (1987). Time
series of geological characteristics may not be essential for understanding
ecosystem dynamics, particularly in the context of living resources.
Because these issues are beyond our expertise, they should be considered
(and currently are) in collaboration with the USGS.
In the case of chemical metrics, we need to identify key chemical indicators
from an array of important nutrients, metals, and toxins. We also need
to be able to track their concentrations through time and space. Few
time series data exist for these chemicals. Some chemicals have been
sampled by our Highlands, NJ Laboratory over time at particular locations.
However, we do not know the spatial extent and resolution of sampling
needed to synoptically understand how these chemicals influence ecosystem
dynamics. Important questions to address include:
how often do we need to sample, what selection of representative chemicals
should we monitor, and what are the major gaps of information? These
questions need to be addressed before we can develop chemical metrics
for this ecosystem.
B. Physical
1. NAO Index
Time: 1823-2000
Spatial: North Atlantic Ocean
Contributed by: Brodziak
Figures A.1 and A.2
Methodology and Data Source
The NAO index is calculated as the air pressure difference between
sites in Iceland and southern locations at the Azores or Gibralter (Jones
et al. 1997). The NAO index time series was computed using data available
from the Climate Research Unit at the University of East Anglia. This
data may be accessed at http://www.cru.uea.ac.uk/.
The NAO winter index is reported here. In year y, the NAO winter index
is the arithmetic average of monthly NAO values for December in year
y and January-March in year y+1. The winter index is available for 1823-2000.
The five-year moving average of the NAO index in year y is computed as
the arithmetic average of NAO values in years y-2, y-1, y, y+1, and y+2;
the five-year average is available for 1825-1998.
Key Points and Major Observations
The North Atlantic Oscillation (NAO) is one of the major features of
the global climate system. There is an upward trend in the NAO from the
1960s to the early 1990s. The NAO index is highly variable and the largest
recorded interannual change in the NAO index occurred from 1994 to 1995.
The latitude of the Gulf Stream has been correlated with the NAO over
the last 30 years (Taylor et al. 1998). Large positive NAO values are
associated with colder air and stronger winds over the North Atlantic
and a larger cold intermediate water layer on the Labrador Shelf. Large
negative NAO values are associated with warmer air and weaker winds over
the North Atlantic and a smaller cold intermediate water layer on the
Labrador Shelf.
2. Shelf wide Temperature anomaly
Time: 1963-2000
Spatial: Shelf wide
Contributed by: Mountain
Figure A.3
Methodology and Data Source
These are the surface and bottom temperature anomalies for NMFS fall
bottom trawl survey, averaged over the whole shelf region from Cape Hatteras
through the Gulf of Maine (Holzwarth and Mountain 1992; Taylor and Bascunan
2001). For each temperature observation made on a survey, its anomaly
was determined by comparison with annual cycles of temperature derived
from the MARMAP program (1978-1987). This procedure takes into account
the day of the year on which the observation was made and its specific
location. All of the anomaly values for a survey were averaged on an
area weighted basis to determine the values plotted.
Key Points and Major Observations
The variability of 2-4 degrees C has been consistently observed over
the past four decades. The late 1960s were a particularly cold period.
The 1990s appear to be slightly warmer than preceding decades.
3. MAB Volume, Salinity & Temperature
anomaly
Time: 1977-2000
Spatial: Mid-Atlantic Bight
Contributed by: Mountain
Figure A.4 (a-c)
Methodology and Data Source
The volume and average temperature and salinity of Shelf Water in the
MAB have been determined for each NEFSC cruise that made temperature
and salinity observations through the MAB area (Mountain 1991). Shelf
Water is defined as water with salinity < 34 PSU, and is in contrast
to the oceanic Slope Water that is found seaward of the shelf/slope front.
From the surveys averaged values for the volume, temperature and salinity
of Shelf Water in the MAB, annual cycles were derived for each variable.
Anomalies for each variable were determined relative to these characteristic
annual cycles
Key Points and Major Observations
There is very large variability in the amount of Shelf Water in the
MAB. Additionally, there is large variability in the salinity of the
Shelf Water in the MAB. The Shelf Water volume in the 1990s was substantially
higher than in the 1980s and the salinity in the 1990s was lower than
in the 1980s. The source of the volume and salinity variations is largely
advective from the Gulf of Maine - and from variation in the inflows
to the Gulf.
4. Surface and Bottom Temperature anomalies
Time: 1963-2000
Spatial: All the major subregions
Contributed by: Mountain, Brodziak
Figure A.5 (a-h)
Methodology and Data Source
These are the surface and bottom temperature anomalies for NMFS bottom
trawl survey, averaged for each of the major subregions (Holzwarth and
Mountain 1992; Taylor and Bascunan 2001). For each temperature observation
made on a survey, its anomaly was determined by comparison with annual
cycles of temperature derived from the MARMAP program (1978-1987). This
procedure takes into account the day of the year on which the observation
was made and its specific location. All of the anomaly values for a survey
were averaged on an area weighted basis to determine the values plotted.
Key Points and Major Observations
There is large variability in the surface and bottom temperatures in
each region. The late 1960s were a particularly cold period. Little trends
are observed in any region through the 1970s and 1980s, although there
may be slightly warmer waters in the 1990s for a few regions. The differences
between the regions show no consistent pattern.
5. MAB Temperature anomalies, by 5 provinces
Time: 1990s, Annual, composite average
Spatial: Mid-Atlantic Bight
Contributed by: Mountain
Figure A.6
Methodology and Data Source
The shelf water temperature anomalies during the 1990s for five regions
of the MAB (from north to south) have been averaged for three periods
of the year (in essence, for thirds of the year) (Mountain 2001). The
anomalies are relative to the MARMAP period (1978-1987). The methods
for determining the shelf water anomalies were describe earlier.Key
Points and Major Observations
During the winters of the 1990s the MAB became progressively warmer
from north to south as compared to the MARMAP period. The summer period
exhibited some cooling in the central MAB. The fall period was generally
a bit warmer than the MARMAP period. Overall, the MAB was about 1 C warmer
in the 1990s than during the MARMAP period.
6. Massachusetts Bay Surface Temperature,
Surface Salinity, Bottom Temperature Anomalies
Time: 1978-2000
Spatial: Massachusetts Bay
Contributed by: J. Jossi
Figure A.7
Methodology and Data Source
These data were collected as part of the MARMAP Ships of Opportunity
Program (Benway et al. In Review; Jossi et al. In Review). Expendable
bathythermograph and surface salinity measurements were taken monthly
by merchant vessels between Boston, MA and Cape Sable, NS. Values were
gridded in time and space (distance along transect). Grids of long term
means and standard deviations; and single year conditions, anomalies,
and standardized anomalies are produced. Grids were sliced through time
at a distance representing Massachusetts Bay for this portrayal, which
also shows a smooth curve based on a 15 month running average (Benway
et al 1993). The location chosen to represent Massachusetts Bay was at
48 km reference distance, or approximately 70o 20'W, along
the transect.
Key Points and Major Observations
Surface Temperature- With the exception of isolated monthly departures
near, or in excess of two standard deviations, the period 1978 through
1988 exhibited no enduring anomalous surface temperatures. From 1992
to mid-1994 mostly colder than average conditions prevailed. No trend
during the time period was apparent.
Surface Salinity- Salinities generally increased from 1978 through
1980, declined through 1984 to a period minimum, rose sharply in 1985,
were below average in 1987, and after 1990 they again declined to the
end of the sampling period in 1993. The longest sustained anomalous period
was that of low salinities in 1983 and 1984.
Bottom Temperature- From 1978 to 1981 values were near normal. Higher
temperatures occurred during 1982 and 1983 followed by near average values
in the mid-1980s. From 1987 through 1990, and 1992 to 1994 values were
generally negative, after which departures became inconsistent, with
several significantly warm months. Departures in the late 1990s were
more excessive than in the earlier period, and might result in a warming
trend for these data.
7. Mid-Atlantic Bight Surface Temperature,
Surface Salinity, Bottom Temperature Anomalies
Time: 1978-2000
Spatial: Mid-Atlantic Bight and mid-Continental Shelf
Contributed by: J. Jossi
Figure A.8
Methodology and Data Source
These data were collected as part of the MARMAP Ships of Opportunity
Program (Benway et al. In Review; Jossi et al. In Review). Expendable
bathythermograph and surface salinity measurements taken monthly by merchant
vessels along a transect from New York City towards Bermuda to the Gulf
Stream. Values were gridded in time and space (distance along transect).
Grids of long term means and standard deviations; and single year conditions,
anomalies, and standardized anomalies are produced. Grids were sliced
through time at a distance representing the continental shelf, generally
unaffected by river runoff and/or slope water, for this portrayal. The
portrayal also shows a smooth curve based on a 15 month running average
(Benway et al. 1993). The location chosen to represent the Middle Atlantic
Bight was at 101 km reference distance, or approximately 40o N;
73o W, along the transect.
Key Points and Major Observations
Surface Temperature- Isolated months through the 1978-2000 time period
exhibit significant departures from the 1978-1990 means. Departures in
excess of 2 standard deviation were more numerous in the 1990s than in
the previous years, even after adjustments to account for the 1990s not
being included in the base period. Sequential, monthly positive or negative
departures were more consistent in the 1990s than in previous years.
Finally, the surface temperatures appear to be trending upwards between
1978 and 2000.
Surface Salinity- Isolated months exhibit significant departures during
the time period, and are more prevalent in especially the late 1990s
than earlier periods. There is more month-to-month consistency of the
surface salinity departures than of the surface temperatures. Uninterrupted
positive departures of two years (1980-1981; 1985-1986; 1994-1995), and
negative departures of two to three years (1996-1998; 1998-1999) occurred.
No trend during the time period was apparent.
Bottom Temperature- Greater departures in the 1990s also occurred in
the bottom temperature data. Aside from beginning the time period in
a negative phase and ending in a positive phase, a possible trend is
not as clear as with surface temperature. However, the phase changes
of the smoothed values are quite similar through the time period for
these two features.
8. W. Gulf of Maine Surface Temperature,
Surface Salinity, Bottom Temperature Anomalies
Time: 1978-2000
Spatial: Gulf of Maine
Contributed by: J. Jossi
Figure A.9
Methodology and Data Source
These data were collected as part of the MARMAP Ships of Opportunity
Program (Benway et al. In Review; Jossi et al. In Review). Expendable
bathythermograph and surface salinity measurements taken monthly by merchant
vessels along a transect from Boston, MA to Cape Sable, NS.. Values were
gridded in time and space (distance along transect). Grids of long term
means and standard deviations; and single year conditions, anomalies,
and standardized anomalies are produced. Grids were sliced through time
at a distance representing approximately Wilkinson Basin for this portrayal.
The portrayal also shows a smooth curve based on a 15 month running average
(Benway et al. 1993). The location chosen to represent the western Gulf
of Maine was at 165 km reference distance, or approximately 68o 55'
W along the transect.
Key Points and Major Observations
Surface Temperature- Variations from 1978 through 1990 followed a similar
pattern to those for surface temperature in Massachusetts Bay, except
that they were of slightly larger magnitude. High values occurred from
1983 to 1985, and low values occurred in 1982, for a fairly prolonged
period from 1986 to 1991, and again from mid-1991 to 1994. This was followed
in 1996 and 1997 by the lowest temperatures of the period, from which
point temperatures began increasing to reach the highest values of the
period by 2000. Neither of these last two conditions were seen to any
extent in Massachusetts Bay. No trend was apparent, although the last
four years of the period exhibited a dramatic increase.
Surface Salinity- The western Gulf of Maine surface salinity pattern
follows that of Massachusetts Bay very closely. The only major exception
was that in the western Gulf of Maine the 1985 high persisted to the
beginning of 1987. No trend was apparent during the time period.
Bottom Temperature- Patterns here were also very similar to those for
bottom temperature in Massachusetts Bay, although the departures were
of less magnitude. Time period low occurred in late-1994 followed by
the series high in 1995. Similarly, variations were larger in the late-1990s
than earlier in the period. No trend was apparent.
9. Relationships
Among NAO, Salinity, Plankton, and Cod on Georges Bank
Time: 1970-1996
Spatial: Georges Bank
Contributed by: Mountain
Figure A.10
Methodology and Data Source
The early spring plankton displacement volume on Georges Bank is compared
with a detrended, inverted NAO series and with salinity variability on
the bank (Mountain et al. 2000). A cod survival index (ratio of the number
of recruits to the spawning stock biomass, with both series hanned before
the ratio was taken) is also compared with the detrended NAO series.
The plankton displacement volume series was determined by J. Kane from
the Center's plankton survey data. The salinity anomalies were derived
from the Center temperature and salinity data, relative to annual cycles
of salinity derived from the MARMAP data set. The cod series were from
stock assessment documents. The NAO was from a NAO website. The method
was straight forward of plotting the predetermined series.
Key Points and Major Observations
The displacement volume appears to follow the detrended NAO and the
salinity variability quite well. There are large interannual differences
in the displacement volume. The cod survivorship series also seems to
follow the NAO quite well. There are no obvious processes that connect
these series.
C. Summary of Abiotic Metrics
Various graphics of temperature and salinity data from Ship-of-Opportunity
(SOOP) data and shelfwide research cruise data were examined. Preliminary
examination of the average of surface and bottom temperatures from the
Autumn Bottom Trawl data, shelf-wide for all regions from Cape Hatteras
to Nova Scotia, showed the 1960s were cold and the remaining years were
variable without any apparent trend. It is questionable if the 1990s
were slightly warmer than preceding decades. When these data are sorted
out spatially into subregions, they exhibit a similar pattern.
Data on the volume of water, salinity and temperature were examined
for the Mid-Atlantic Bight (MAB) shelf water inside the shelf/slope boundary.
In the 1990s, the following were observed: 1) a 25-30% increase in the
amount of shelf water volume in the Bight was apparent over that of the
long term mean; 2) salinity was lower in the 90s; similar to observations
made for northwestern Georges Bank; and 3) temperature was about 1 degree
warmer in the 90s.
The MAB data were broken out into shelf sectors (SNE, NYB1, NYB2, SS1,
SS2, north to south orientation). It was noted that the apparent warming
in the MAB in the 1990s concentrated in the southern regions (SS1, SS2)
during the winter. Atmospheric heat flux seems the likely source and
needs to be investigated. Further, there is some indication that advective
events present in the Gulf of Maine (GOM) have affected SNE and NYB temperature
and salinity. For example, GLOBEC data indicates a shift in the basic
circulation into GOM from 1 part Scotian Shelf water and 2 parts Oceanic
current, to 2 parts Scotian Shelf and 1 part Oceanic water. Documentation
of changes in the major inflows into the GOM is needed.
Given the extent of the variability in the data, what metrics are useful
to see system-wide changes? Several data sets were examined relative
to the detrended North Atlantic Oscillation (NAO) which shows significant
3-5 year variability over a strong 30 year trend. Large changes in zooplankton
volume occurred over the 1970-1995 period. Volumes decreased in the early
1980s, followed by a large increase in 1985-1990 period. Plankton volume
fluxes correlated with the detrended, inverse of the NAO (see chapter
4 for further details). Plankton volume and salinity anomalies may have
a relationship and other covarying parameters may exist. These relationships
merit further examination. Additionally, an index of cod recruitment
and standing stock biomass (SSB) data correlate with the detrended, inverted
NAO data. Possible relationships between the cod survival anomaly, the
SSB and detrended NAO data also merit examination. Chlorophyll data is
also needed to help corroborate production, particulary of the plankton
(i.e., volume) and the NAO trends.
No linkage is apparent between offshore waters and the NAO events of
the 1960s through the 1990s, however, the linkage between coastal water
temperatures and NAO needs to be examined.
D. References
Backus, R.H. 1987. Georges Bank. MIT Press, Cambridge, Massachusetts.
Benway, R.L. and Jossi, J.W. In Review. Ships of opportunity (SOOP)
sampling. In: Jossi, J.W. and Griswold, C.A. (eds.) In Review.
MARMAP Ecosystem Monitoring: Operations Manual. NOAA Technical Memorandum
NMFS-F/NEC.
Benway, R.L., Jossi, J.W., Thomas, K.P., and Goulet, J.R. 1993. Variability
of temperature and salinity in the Middle Atlantic Bight and Gulf of
Maine. NOAA Technical Report NMFS, 112.
Holzwarth, T. and Mountain, D. 1992. Surface and bottom temperature
distributions from the Northeast Fisheries Center spring and fall bottom
trawl survey program, 1963-1987, with addendum for 1988-1990. National
Marine Fisheries Service, Northeast Fisheries Science Center, Center
Reference Document 90-03.
Jones, P.D., Jonsson, T. and Wheeler, D. 1997. Extension of the North
Atlantic Oscillation using early instrumental pressure observations from
Gibralter and southwest Iceland. Int. J. Climatol. 17:1433-1450.
Jossi, J.W., Benway, R.L., and Goulet, J.R. In Review. MARMAP Ecosystem
Monitoring: Program Description. NOAA Technical Memorandum NMFS-F/NEC.
Mountain, D. 1991. The volume of shelf water in the Middle Atlantic
Bight: seasonal and interannual variability, 1977-1987. Continental Shelf
Res., 11, 251-267.
Mountain, D. 2001. Variability in the properties of Shelf Water in
the Middle Atlantic Bight, 1977-1999. JGR (submitted).
Mountain, D., Kane, J. and Green, J.. 2000. Environmental forcing and
variability in zooplankton abundance and cod recruitment on Georges Bank.
ICES CM 2000/M:15.
Taylor, A.H. and Stephens, J.A. 1998. The North Atlantic Oscillation
and the latitude of the Gulf Stream. Tellus, 50A: 134-142.
Taylor, M.H. and Bascunan, C. 2001. Description of the 2000 oceanographic
conditions on the northeast continental shelf. National Marine Fisheries
Service, Northeast Fisheries Science Center, Center Reference Document
01-01.
IV. BIOTIC METRICS
(Click here for PDF Version)
A. Phytoplankton
1. US Northeast Continental Shelf Ecosystem, Chlorophyll-a
Time: 1977-1988
Spatial: US Northeast Shelf Ecosystem (Shelf wide)
Contributed by: J. Jossi and J.E. O'Reilly
Methodology and Data Source
These data were collected as part of the MARMAP Program. Six to twelve
research vessel surveys/year undertook water column sampling of phyto-pigments
in the euphotic zone (O'Reilly and Zetlin 1998).
Key Points and Major Observations
Fifty-seven thousand eighty-eight measurements were made during 78
oceanographic surveys from 1977 through 1988. Extensive horizontal, vertical,
and seasonal distributions are portrayed. No time series per se has been
constructed. Not much inter-annual change in chlorophyll a is
observed.
B. Birds
We recognize that birds are an important part of this ecosystem, but
few time series data are available for these species. Although there
is some extant data, no one from the group provided data for this report.
Certainly this is an important issue to consider for some species, and
merits further examination in the future. In fact, basic questions such
as "what are the trends in abundance of major species?" remain unanswered.
How often do we need to sample to better answer these questions? What
spatial extent and resolution do we need? What are the most cost effective
methodologies?
C. Turtles
We also recognize that turtles are an important part of this ecosystem,
but few time series data are available for these species. Although there
is some extant data, no one from the group provided data for this report.
See Palka et al. (In review) for some estimates of turtle abundance for
selected years in the 1990s. Certainly this is an important issue to
consider for some species, and merits further examination in the future.
D. Benthos
In general, few time series data are available for the benthos. Classic
shelf-wide studies were conducted by Theroux and Wigley (1998). Other
studies have covered smaller areas, and synoptic, shelf-wide information
is generally lacking. However, a few components of the benthic community
are surveyed regularly.
1. Georges Bank, Mid-Atlantic Bight Scallop
Biomass, Landings, and Survey Indices
Time: 1962-1999 (Landings & Survey), 1980-2000 (Biomass)
Spatial: Georges Bank, Mid Atlantic Bight
Contributed by: Hart
Figures B.1, B.2, B.3, B.4
Methodology and Data Source
These data were collected from the NMFS sea scallop survey and landings
database. Biomass was poststratified into open and closed areas. For
further details see NEFSC (2001) and Murawski et al. (2000).
Key Points and Major Observations
Biomass was at low levels through 1994 due to increasingly severe overfishing.
This resulted in highly variable landings well below optimal levels,
driven primarily by sporadic recruitment events. After area closures
(December 1994 in Georges Bank, April 1998 in Mid-Atlantic), there was
a rapid buildup of biomass in the closed areas. The limited amount of
fishing permitted in the closed areas in 1999-2000 does not appear to
have substantially impacted the biomass there. Biomasses in open areas
have increased recently due to effort reductions and good recruitment.
Recent good recruitment on both Georges Bank and Mid-Atlantic may be
related to the increased levels of spawning-stock biomass in the closed
areas.
2. Sculpin abundance from fall bottom trawl
survey
Time: 1963 - 1998
Spatial: Southern New England and Georges Bank
Contributed by: Link
Figure B.5
Methodology and Data Source
These data were collected as part of the NEFSC Habitat Research Program
and standard bottom trawl survey. The stratified mean trawl catch per
tow (Azarovitz 1981) was calculated for this species. See Link and Almeida
(2002) for further details.
Key Points and Major Observations
Longhorn sculpin abundance peaked in the mid 1960s and then exhibited
a relatively steady period for the first 15 years of the survey. This
was followed by a period of lower abundance during the mid 1980s and
an increasing trend in the 1990s. In most years sculpin abundance ranged
from 10 to 20 fish per tow. The years with highest index of sculpin abundance
were 1966 and 1998. Relative to the several preceding years, the index
of sculpin abundance notably increased during 1966, 1987 and 1998.
3. Blue crab abundance
Time: July 1996 - October 2000 (spring, summer, and fall)
Spatial: Navesink River and Sandy Hook Bay in the mid-Atlantic region
Contributed by: Fabrizio
Figure B.6
Methodology and Data Source
These data were collected as part of the Behavioral Ecology Survey
of Demersal Species in Navesink River. Three seasonal collections were
made in the spring, summer, and fall beginning in the summer of 1996.
Demersal species were collected by replicate tows of a 1-m beam and a
5- m otter trawl at 84 stations throughout the Navesink River and Sandy
Hook Bay. Beginning in July 1998, only 24 stations were sampled throughout
this system. All fish and decapod crustaceans were enumerated and environmental
characteristics were measured. The data in the figure represent the mean
number of blue crabs per m2 across all stations in the Navesink
River and Sandy Hook Bay (Meise and Stehlik In Press).
Key Points and Major Observations
Blue crab abundance increased in 1998-1999 in the Navesink River-Sandy
Hook Bay estuarine system, but declined by 2000. These data are from
a short time series with limited spatial coverage, but are important
to the local estuarine dynamics.
E. Zooplankton
1. Central Gulf of Maine Calanus finmarchicus,
c.1-4, c.5-6 anomalies
Time: 1961-1990
Spatial: Central Gulf of Maine
Contributed by: Jossi
Figure B.7 (a-b)
Methodology and Data Source
These data were collected as part of the MARMAP Ships of Opportunity
Program (Benway et al. In Review; Jossi et al. In Review). Continuous
Plankton Recorders were towed monthly by merchant vessels along a transect
from Boston, MA to Cape Sable, NS. Zooplankton and larger phytoplankton
were captured, identified and enumerated. Abundance values were gridded
in time and space (distance along transect). Grids of long term medians,
means and standard deviations; and single year conditions, anomalies,
and standardized anomalies are produced. Grids were sliced through time
at a distance representing the central Gulf of Maine in this portrayal.
The portrayal also shows a smooth curve based on a 15 month running average
(Jossi and Goulet 1993; Pershing et al. 2001).
Key Points and Major Observations
A biphase pattern has been found in this, and several other of the
dominant zooplankton taxa of the Gulf of Maine during the 1961-1990 period
(Jossi and Goulet, 1993), and also an uptrend for the adult stages of Calanus
finmarchicus. Also, the adult stages of this taxon have exhibited
a positive (with lag) correlation with the winter North Atlantic Oscillation
(Pershing et al. 2001).
2. Anomalies of major zooplankton during
spring
Time: 1977 - 1996, Spring (15 Feb- 15 May)
Spatial: Georges Bank
Contributed by: Jossi
Figure B.8
Methodology and Data Source
These data were collected as part of the MARMAP Surveys (Benway et
al. In Review; Jossi et al. In Review). Zooplankton and larger phytoplankton
were captured, identified and enumerated. Abundance values were gridded
in time and space (distance along transect). Single year conditions,
anomalies, and standardized anomalies are produced.
Key Points and Major Observations
The community composition has changed notably over time. Yet there
are no apparent trends in total zooplankton abundance and no major departures
from zero even though predator biomass has changed greatly during the
time period.
3. Time and space conditions of Centropagus
typicus across the continental shelf
Time: 1976 - 1990, averaged
Spatial: transect from New York to Bermuda
Contributed by: Jossi
Figure B.9
Methodology and Data Source
These data were collected as part of the MARMAP Ships of Opportunity
Program (Benway et al. In Review; Jossi et al. In Review). Continuous
Plankton Recorders were towed monthly by merchant vessels along a transect
from New York to Bermuda. Zooplankton and larger phytoplankton were captured,
identified and enumerated. Abundance values were gridded in time and
space (distance along transect). Grids of long term medians, means and
standard deviations; and single year conditions, anomalies, and standardized
anomalies are produced. Key Points and Major Observations
An impressive color figure captures seasonal and local spatial dynamics
well, although this is not a time series per se.
4. Calanus abundance by day of
year over time
Time: 1961-1998
Spatial: transect from Boston, Mass. to Cape Sable
Contributed by: Jossi
Figure B.10
Methodology and Data Source
These data were collected as part of the MARMAP Ships of Opportunity
Program (Benway et al. In Review; Jossi et al. In Review). Continuous
Plankton Recorders were towed monthly by merchant vessels along a transect
from Boston, MA to Cape Sable, NS. Zooplankton and larger phytoplankton
were captured, identified and enumerated. Abundance values were gridded
in time and space (distance along transect), and in this case, gridded
in time (years) vs time (days of year). This portrayal shows changes
of seasonality for the Gulf of Maine as a whole during the 38 year time
span.
Key Points and Major Observations
During the mid 1980s, Calanus finmarchicus shows up later
and leaves earlier. In the early1990s there is an even earlier appearance
of this species. Can these timing changes be related to the changing
oceanographic conditions over this time period?
5. The overall zooplankton biomass and
abundance trends of two dominant copepods: Calanus finmarchicus and Centropages
typicus
Time: 1977 - 2000
Spatial: Georges Bank and Gulf of Maine
Contributed by: Kane
Figures B.11 and B.12
Methodology and Data Source
These data were collected as part of the MARMAP Surveys (Benway et
al. In Review; Jossi et al. In Review). Zooplankton samples were collected
at approximately bimonthly intervals throughout the region with a 0.333-mm
mesh net fitted on one side of a 61-cm bongo frame. Biomass was measured
by displacement volume and individual species were sorted and counted
from sub samples. Data in the figures represent ranked departures from
the time series monthly means with a fourth order polynomial fit to the
data. See Kane (1993), Sherman et al. (1998), and Kane (1999) for further
details.
Key Points and Major Observations
Zooplankton trends in both regions were similar. Biomass was usually
high in the late seventies, low throughout most of the eighties, and
highly variable during the 1990s. The biomass trend line on Georges Bank
during the 1990s is higher because of high values recorded in 1989 and
1990, years where budget constraints prevented sampling in the GOM. Calanus
finmarchicus abundance was high in the late seventies and highly
variable during the past two decades with no persistent long-term trend. Centropages
typicus density was high from 1978-82, low throughout the remainder
of the 1980s, and above average during the past decade.
6. Total Zooplankton Biomass
Time: 1977-2000
Spatial: Shelf wide
Contributed by: Kane
Figure B.13
Methodology and Data Source
These data were collected as part of the MARMAP Surveys (Benway et
al. In Review; Jossi et al. In Review). Zooplankton samples were collected
at approximately bimonthly intervals throughout the region with a 0.333-mm
mesh net fitted on one side of a 61-cm bongo frame. Biomass was measured
by displacement volume and individual species were sorted and counted
from sub samples. Data in the figures represent ranked departures from
the time series monthly means with a fourth order polynomial fit to the
data. See Kane (1993), Sherman et al. (1998), and Kane (1999) for further
details.
Key Points and Major Observations
Biomass was generally higher in the late 1970s, with no persistant
long term trend during the past two decades. There was a lot of variability
in the data. Patterns are similar in each of the four main subregions.
F. Fish and Squids
For the majority of these organisms, we refer the reader to NEFSC (1998a,
1998b, 1998c, 2000a, 2000b, 2000c, 2001). These documents contain individual
species stock assessments and annual reports on the status of the major
or commerically valuable species.
1. Relative abundance of northeast species
groups (groundfish, pelagics, elasmobranchs, others) from combined
fall and spring bottom trawl surveys
Time: 1963 - 1999
Spatial: Shelf wide
Contributed by: NEFSC
Figure B.14 (a-d)
Methodology and Data Source
These data were collected as part of the NEFSC Bottom Trawl Survey
(Azarovitz 1981; NEFC 1988). Species were aggregated as principal groundfish,
other groundfish, principal pelagics, and elasmobranchs. A stratified
mean biomass per tow was calculated and smoothed over the time series.
Key Points and Major Observations
The abundance of principal groundfish declined through the mid 1970s,
increased slightly in the late 1970s and early 1980s, and declined thereafter,
remaining at low levels through the 1990s. The abundance of pelagic fishes
declined in the 1970s and increased substantially and continuously thereafter.
Elasmobranch abundance increased from the 1960s through the 1990s, then
declined moderately in the late 1990s. The abundance of other groundfish
has fluctuated without trend. These observations suggest a shift in community
structure and food web dominance.
2. Principal groundfish biomass for Georges
Bank from autumn bottom trawl survey
Time: 1963 - 1999
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.15
Methodology and Data Source
The principal groundfish index is the sum of indices of 12 principal
(exploited) groundfish on Georges Bank. These species include Atlantic
cod (Gadus morhua), haddock (Melanogrammus aeglefinus),
redfish (Sebastes fasciatus), silver hake (Merluccius bilinearis),
red hake (Urophyscis chuss), pollock (Pollachius virens),
yellowtail flounder (Limanda ferruginea), summer flounder (Paralichthys
dentatus), American plaice (Hippoglossoides platessoides),
witch flounder (Glyptocephalus cynoglosses), winter flounder
(Pseudopleuronectes americanus), and windowpane flounder (Scophthalmus
aquosus). The individual indices are stratified mean weight per
tow during autumn, calculated with survey gear adjustment factors applied
where appropriate using NEFSC offshore survey strata 9-23 and 25. See
Brodziak and Link (2002) and Azarovitz (1981) for further details.
Key Points and Major Observations
A large decline in principal groundfish occurred during 1960s and early
1970s. A moderate increase occurred during the late-1970s and early 1980s.
Principal groundfish abundance declined through the 1990s, although recently
there has been a moderate increase.
3. Elasmobranch biomass for Georges Bank
from autumn bottom trawl survey
Time: 1968 - 2000
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.16
Methodology and Data Source
The elasmobranch index is the sum of indices of 6 primary elasmobranchs
on Georges Bank. These species include spiny dogfish (Squalus acanthius),
barndoor skate (Raja laevis), thorny skate (Raja radiata),
smooth skate (Raja senta), winter skate (Raja ocellata),
and little skate (Raja erinacea). The individual indices are
stratified mean weight per tow during spring, calculated with survey
gear adjustment factors applied where appropriate using NEFSC offshore
survey strata 9-23 and 25. See Brodziak and Link (2002) and Azarovitz
(1981) for further details.
Key Points and Major Observations
Elasmobranch biomass was low in the 1970s. Elasmobranch biomass increased
to high values in the 1980s and early1990s. Elasmobranch biomass has
decreased in the late1990s.
4. Principal pelagics biomass estimates
from recent assessments
Time: 1967 - 1994
Spatial: entire range of population in the northwest Atlantic (shelf wide)
Contributed by: Brodziak
Figure B.17
Methodology and Data Source
These data were derived from the NEFSC assessments of pelagics species.
Age-structured assessments using sequential population analysis tuned
to NEFSC survey abundance-at-age indices were used. See Brodziak and
Link (2002) and NEFSC (1998a) for further details.
Key Points and Major Observations
The principal pelagics (Altantic herring Clupea harengus and
Atlantic mackerel Scomber scombrus) are migratory resources
that were heavily fished by distant water fleets in the 1960s-1970s.
Abundance of principal pelagics was high (or moderate) in the early-1970s
and declined to record lows in the 1970s and early-1980s. Abundance was
high and increasing in the late-1980s through the 1990s.
5. Cephalapod biomass for Georges Bank
from fall bottom trawl survey
Time: 1967 - 1999
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.18
Methodology and Data Source
The cephalopod biomass index is the sum of indices of two principal
(exploited) cephalopods, long-finned squid (Loligo pealeii)
and northern short-finned squid (Illex illecebrosus), along
with other squid and octopuses on Georges Bank. The individual indices
are stratified mean weight per tow during autumn, calculated with survey
gear adjustment factors applied where appropriate using NEFSC offshore
survey strata 9-23 and 25. See Brodziak and Link (2002) and Azarovitz
(1981) for further details.
Key Points and Major Observations
Cephalopods are short-lived (lifespan< 1 year) and are common prey
for many species. Distribution of the two primary squids on Georges Bank
depends on seasonal changes in water temperatures. Cephalopod abundance
increased during the late-1960s to late-1970s, declined to the mid-1980s,
and increased in the late-1980s. Abundance declined during the early
1990s and has increased moderately since 1996.
6. Frequency of occurrence of parasitic
nematodes in all predators
Time: 1973 - 1998 in five year blocks
Spatial: Shelf wide
Contributed by: Link
Figure B.19
Methodology and Data Source
These data were derived from the NEFSC Food Habits Database. Live nematodes
observed in examined stomachs were noted. See Link and Almeida (2000)
for further details.
Key Points and Major Observations
There was a methodological shift between 1980 and 1981, so the apparent
trend may be misleading. Otherwise nematode occurrence may provide an
index of density dependent health in fish.
7. Winter flounder collected by beam and
otter trawls
Time: July 1996 - October 2000 (spring, summer, and fall)
Spatial: Navesink River and Sandy Hook Bay in the mid-Atlantic region
Contributed by: Fabrizio
Figure B.20
Methodology and Data Source
These data were collected in the Behavioral Ecology Survey of Demersal
Species. Three seasonal collections were made in the spring, summer,
and fall beginning in the summer of 1996. Demersal species were collected
by replicate tows of a 1-m beam and a 5- m otter trawl at 84 stations
throughout the Navesink River and Sandy Hook Bay. Beginning in July 1998,
only 24 stations were sampled throughout this system. All fish and decapod
crustaceans were enumerated and environmental characteristics were measured.
The data in the figure represent the mean number of winter flounder per
m2 across all stations in the Navesink River and Sandy Hook
Bay.
See Stehlik and Meise (2000) and Stoner et al. (2001) for further details.
Key Points and Major Observations
Beam trawls captured newly settled winter flounder, and generally not
older stages.
As indicated by the beam trawl samples, young-of-the-year winter flounder
abundance was high in the spring of 1999. These data are from a short
time series with limited spatial coverage, but are important to the local
estuarine dynamics.
8. Haddock and cod % maturity for ages
1 and 2
Time: 1963 - 1997 in five year blocks (haddock) and 1978 - 1997 in four
year blocks (cod)
Spatial: Georges Bank
Contributed by: NEFSC SARCs
Figure B.21
Methodology and Data Source
These data are from the NEFSC Age Database (SVBIO) collected as part
of the bottom trawl survey. The particular analyses for these species
can be found in NEFSC (1998b, 1998c, 2000a, 2000b, 2000c, 2001).
Key Points and Major Observations
Haddock seem to show an increase in early maturity over time. How do
changes in maturity reflect ecosystem level effects?
9. Cod survival ratio anomaly
Time: 1978 - 1998
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.22
Methodology and Data Source
The cod survival ratio anomaly measures the difference between the
observed value of cod recruitment per unit of spawning biomass (survival
ratio index) and its predicted value from a fitted Beverton-Holt stock-recruitment
curve. Higher anomaly values are associated with more favorable recruitment
conditions. See Brodziak and Link (2002) for further details.
Key Points and Major Observations
The Georges Bank cod survival ratio anomaly has no apparent trend during
1978-1998, although anomaly values were negative in the late 1980s-early
1990s and have been more positive since 1995. Georges Bank cod recruitment
has been low in recent years and this data suggests that this is not
primarily due to adverse environmental conditions. Survival ratio anomaly
measures deviation of recruits per spawner from a spawner recruit relationship.
10. Haddock survival ratio anomaly
Time: 1931 - 1998
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.23
Methodology and Data Source The haddock survival ratio anomaly
measures the difference between the observed value of haddock recruitment
per unit of spawning biomass (survival ratio index) and its predicted
value from a fitted Beverton-Holt stock-recruitment curve. Lower anomaly
values are associated with less favorable recruitment conditions. See
Brodziak and Link (2002) for further details.
Key Points and Major Observations
Georges Bank haddock survival ratio anomalies appear to be higher during
the 1930s-early 1960s than during the late1960s-1990. The two largest
anomalies correspond to the 1963 and 1975 year classes which were very
large based on assessment results (i.e., the two "super year classes" are
apparent). Survival ratio anomaly measures deviation of recruits per
spawner from a spawner recruit relationship.
11. Yellowtail flounder survival ratio
anomaly
Time: 1973 - 1997
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.24
Methodology and Data Source
The yellowtail survival ratio anomaly measures the difference between
the observed value of yellowtail flounder recruitment per unit of spawning
biomass (survival ratio index) and its predicted value from a fitted
Beverton-Holt stock-recruitment curve. See Brodziak and Link (2002) for
further details.
Key Points and Major Observations
There appears to be an increasing trend in the survival ratio anomaly
since the mid-1980s. Since area II was closed on Georges Bank in 1994,
the survival ratio anomalies have been relatively high. Survival ratio
anomalies for Georges Bank yellowtail flounder appear to be more variable
than for cod or haddock. Survival ratio anomaly measures deviation of
recruits per spawner from a spawner recruit relationship.
G. Mammals
1. Several marine mammal trends
Time: Various years in the 1980s, 90s
Spatial: Shelf wide
Contributed by: Palka, Smith
Table 4.1
Methodology and Data Sources
Abundance of harbor seals were estimated as the total
count of hauled out animals that were estimated from aerial photos of
animals hauled out during the pupping season on the New England coast
(Gilbert and Guldager 1998). This abundance is considered a minimum estimate
because it was not corrected for animals in the water or outside the
survey area.
Data for all other species were collected during sighting line transect
surveys conducted by planes (1982, 1995, 1998, and 1999) and/or ships
(1991-1999). Shipboard data were collected using the two independent
sighting team procedure and were analyzed using the product integral
or modified direct duplicate methods (Palka 1995). These estimates were
corrected for g(0), the probability of detecting a group on
the track line and, if applicable, also for school size-bias. Standard
aerial sighting procedures with two bubble windows and one belly window
observer were used during the aerial surveys. An estimate of g(0) was
not made for the aerial portion of the surveys, except for harbor porpoises
from surveys conducted after 1990. For a brief overview of all survey
results, see CETAP (1982), Smith et al. (1993), Palka (1996), Palka (2000),
Waring et al. (2000), Mullin (In review) and Palka et al. (In review).
Key Points and Major Observations
These surveys were conducted in different areas within the US and Canadian
Northwest Atlantic Ocean, thus, it is not possible to directly compare
the reported numbers. Most of these estimates are negatively biased due
to not accounting for dive times, ship reaction, and animals outside
of the surveyed area. These biases vary by species. Estimates from1998/1999
are generally the largest, and the best recent estimates, because the
surveys covered waters from Florida to the Gulf of St. Lawrence, the
largest portion of the animal=s habitat that was ever covered.
H. Aggregate
1. Total biomass from both fall and spring
bottom trawl surveys
Time: 1963 - 2000
Spatial: Shelf wide
Contributed by: Link
Figure B.25 (a-b)
Methodology and Data Source
These data were collected as part of the NEFSC Bottom Trawl Survey
(Azarovitz 1981; NEFC 1988). Biomass of all net-caught organisms was
aggregated irrespective of species, and a stratified mean biomass per
tow was calculated over the time series. Both a mean per tow and minimum
swept area estimate of total biomass were calculated.
Key Points and Major Observations
There is no apparent trend in total biomass from the mid 1960s to 2000s.
The may reflect an overall system carrying capacity. The implication
is that if we want to simulataneously rebuild/restore all major groups,
then other components of the ecosystem will have to decline. Can fluctuations
in total biomass be linked to the physical environment? This raises the
question of examining standing stock vs productivity (changes in trophic
transfer) of the different component species. The bottom trawl is not
highly selective for pelagics, jellyfish, plankton, etc., and no corrections
for selectivity were made. The jump in biomass during the late 1960s
could be due to adding the spring survey in 1968.
2. Mean length of all species collected
in fall and spring bottom trawl
Time: 1963 - 2000
Spatial: Georges Bank
Contributed by: Link
Figure B.26
Methodology and Data Source
These data were collected as part of the NEFSC Bottom Trawl Survey
(Azarovitz 1981; NEFC 1988). Organisms were aggregated irrespective of
species, and a stratified mean length for each year was calculated over
the time series.
Key Points and Major Observations
Lengths were lower through the mid 1970s, and longer in the late 1970s
through early 1990s. Lengths were again shorter in the mid to late 1990s.
Does this infer regime shifts, or could it just be the effect of dogfish
and skates? The peak length corresponds to the period when herring and
other pelagics were low in abundance.
3. Abundance of various guilds in fall
and spring bottom trawl surveys
Time: 1963 - 2000
Spatial: Shelf wide
Contributed by: Link
Figure B.27 (a-l)
Methodology and Data Source
These data were collected as part of the NEFSC Bottom Trawl Survey
(Azarovitz 1981; NEFC 1988). Species were aggregated into appropriate
guilds (Garrison and Link 2000), and a stratified mean biomass per tow
was calculated and smoothed over the time series. Both a mean per tow
and minimum swept area estimate of total biomass were calculated.Key
Points and Major Observations
These results are similar to other graphs of grouped biomass. Do these
better convey information better than groupings by taxonomy? Guilds may
be an useful approach, and certainly provide a slightly different picture
of fish community dynamics than the taxonomic groupings.
I. Community Indices
1. Gulf of Maine total species diversity
from bottom trawl survey
Time: 1963 - 2000
Spatial: Gulf of Maine
Contributed by: Brodziak
Figure B.28
Methodology and Data Source
Total species diversity was indexed by the average number of species
per haul during the autumn bottom trawl survey in Gulf of Maine offshore
strata. See Brodziak and Link (2002) for related details, and Ludwig
and Reynolds (1988) for a further discussion of diversity.
Key Points and Major Observations
This diversity index has an increasing trend since late 1980s. The
most recent index value is the highest in time series. This measure may
have been impacted by decisions regarding recording of species during
trawl survey cruises.
2. Gulf of Maine abundant species diversity
from bottom trawl survey
Time: 1963 - 2000
Spatial: Gulf of Maine
Contributed by: Brodziak
Figure B.29
Methodology and Data Source
Abundant species diversity was indexed by the average number of abundant
species (N1) per haul during the autumn bottom trawl survey in Gulf of
Maine offshore strata. N1 was computed as the N1=eH , where
H was Shannon's diversity index evaluated in terms of the biomass proportion
within a trawl sample. See Brodziak and Link (2002) for related details,
and Ludwig and Reynolds (1988) for a further discussion of diversity.
Key Points and Major Observations
This diversity index peaked in the early 1980s. This index provides
a measure of species dominance.
3. Gulf of Maine species evenness from
bottom trawl survey
Time: 1963 - 2000
Spatial: Gulf of Maine
Contributed by: Brodziak
Figure B.30
Methodology and Data Source
This is Hill's modified evenness index (see for example, Ludwig and
Reynolds 1988). Species evenness was indexed by the average of the ratio
(N2-1)/(N1-1) during the autumn bottom trawl survey in Gulf of Maine
offshore strata. N2 was computed as the inverse of Simpson's diversity
index, evaluated in terms of the biomass proportion within a trawl sample.
See Brodziak and Link (2002) for related details, and Ludwig and Reynolds
(1988) for a further discussion of diversity.
Key Points and Major Observations
Species evenness has a decreasing trend since the early 1980s. Current
evenness values are the lowest in the time series. The decreasing trend
in evenness may be due to the abundance of large skates in some areas
of the Gulf of Maine.
4. Georges Bank total species diversity
from bottom trawl survey
Time: 1963 - 2000
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.31
Methodology and Data Source
Total species diversity was indexed by the average number of species
per haul during the autumn bottom trawl survey in Georges Bank strata.
See Brodziak and Link (2002) for related details, and Ludwig and Reynolds
(1988) for a further discussion of diversity.
Key Points and Major Observations
This diversity index appears to trend up and down throughout the observed
time series. Total species diversity on Georges Bank has trended upward
since the early 1990s after declining to a time series low during the
1980s. This measure may have been impacted by decisions regarding recording
of species during trawl survey cruises.
5. Georges Bank abundant species diversity
from bottom trawl surveys
Time: 1963 - 2000
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.32
Methodology and Data Source
Abundant species diversity was indexed by the average number of abundant
species (N1) per haul during the autumn bottom trawl survey in Georges
Bank strata. N1 was computed as the N1=eH , where H was Shannon's
diversity index evaluated in terms of the biomass proportion within a
trawl sample. See Brodziak and Link (2002) for related details, and Ludwig
and Reynolds (1988) for a further discussion of diversity.
Key Points and Major Observations
This species dominance index was higher during the 1960s-1970s than
during the 1980s. In recent years, abundant species diversity has exhibited
an increasing trend. This metric is a measure of dominance.
6. Georges Bank species evenness from bottom
trawl surveys
Time: 1963 - 2000
Spatial: Georges Bank
Contributed by: Brodziak
Figure B.33
Methodology and Data Source
This is Hill's modified evenness index (see for example, Ludwig and
Reynolds 1988). Species evenness was indexed by the average of the ratio
(N2-1)/(N1-1) during the autumn bottom trawl survey in Georges Bank strata.
N2 was computed as the inverse of Simpson's diversity index, evaluated
in terms of the biomass proportion within a trawl sample. See Brodziak
and Link (2002) for related details, and Ludwig and Reynolds (1988) for
a further discussion of diversity.
Key Points and Major Observations
Species evenness on Georges Bank peaked in the early 1970s. This index
steadily decreased during 1975-1990 and has only increased a small amount
in recent years.
7. Mid-Atlantic Bight total species diversity
from bottom trawl surveys
Time: 1963 - 2000
Spatial: Mid-Atlantic Bight
Contributed by: Brodziak
Figure B.34
Methodology and Data Source
Total species diversity was indexed by the average number of species
per haul during the autumn bottom trawl survey in Mid-Atlantic Bight
offshore strata. See Brodziak and Link (2002) for related details, and
Ludwig and Reynolds (1988) for a further discussion of diversity.
Key Points and Major Observations
This diversity index has no apparent trend.
8. Mid-Atlantic Bight Abundant species
diversity from bottom trawl surveys
Time: 1963 - 2000
Spatial: Mid-Atlantic Bight
Contributed by: Brodziak
Figure B.35
Methodology and Data Source
Abundant species diversity was indexed by the average number of abundant
species (N1) per haul during the autumn bottom trawl survey in Gulf of
Maine offshore strata. N1 was computed as the N1=eH , where
H was Shannon's diversity index evaluated in terms of the biomass proportion
within a trawl sample. See Brodziak and Link (2002) for related details,
and Ludwig and Reynolds (1988) for a further discussion of diversity.
Key Points and Major Observations
This measure of species dominance has no apparent trend.
9. Mid-Atlantic Bight Species evenness
from bottom trawl survey
Time: 1963 - 2000
Spatial: Mid-Atlantic Bight
Contributed by: Brodziak
Figure B.36
Methodology and Data Source
This is Hill's modified evenness index (see for example, Ludwig and
Reynolds 1988). Species evenness was indexed by the average of the ratio
(N2-1)/(N1-1) during the autumn bottom trawl survey in Gulf of Maine
offshore strata. N2 was computed as the inverse of Simpson's diversity
index, evaluated in terms of the biomass proportion within a trawl sample.
See Brodziak and Link (2002) for related details, and Ludwig and Reynolds
(1988) for a further discussion of diversity.
Key Points and Major Observations
Species evenness has had no apparent trend in the Mid-Atlantic Bight.
J. Food Web Indices
1. Silver hake linkage density
Time: 1973 - 1998
Spatial: Shelf wide
Contributed by: Link
Figure B.37
Methodology and Data Source
These data are derived from the NEFSC Food Habits Database. See Link
and Almeida (2000) for further details on the food habits sampling.Key
Points and Major Observations
This metric measures number of species eating and being eaten by silver
hake. Silver hake is a "canary" population because a large amount of
energy passes through this species, i.e., it eats many species and many
species eat it. The same is true for red hake (not shown). The number
of prey species consumed by silver hake declined in the mid 1980s, but
has increased through the mid 1990s. Do these changes reflect an overall
change in number of species in ecosystem?
2. Total consumption by 12 piscivores
Time: 1977 - 1997
Spatial: primarily Georges Bank
Contributed by: Overholtz
Figure B.38
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption estimation, see
Overholtz et al. (2000).
Key Points and Major Observations
Total consumption (all prey) by 12 predatory fish (pollock, goosefish,
cod-2 stocks, spiny dogfish, white hake, weakfish, winter skate, summer
flounder, bluefish, red hake, spotted hake, and silver hake) averaged
1.5 million mt and ranged between 1.3 and 2.9 million mt during 1977-1997.
Consumption peaked in the early 1980s and declined steadily through 1997.
This trend is consistent with the large biomass of elasmobranchs and
groundfish that were present during the 1980s and a subsequent large
decline in spiny dogfish, cod, white hake, and bluefish, due to fishing,
during the later period. Total annual consumption by individual predators
was lowest by goosefish and summer flounder and highest by silver hake,
and spiny dogfish. Consumption estimates for individual predator species
spanned nearly three orders of magnitude and was heavily influenced by
predator abundance. As an example, spiny dogfish consumed an average
of 619,000 mt, bluefish, 108,000 mt, and goosefish, 14,000 mt during
1977-1997.
3. Total fish consumption by six piscivores
on Georges Bank
Time: 1977 - 1998 in three year blocks
Spatial: Georges Bank
Contributed by: Link
Figure B.39
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption estimation, see
Link and Garrison (2002a).
Key Points and Major Observations
There was a peak in the early 1980s due to an abundance of extra large
cod. Consumption by silver hake and cod dominated 1977 and 1980 values;
consumption by dogfish dominated the rest of the time series. The total
consumption was relatively consistent aside from the one peak.
4. Consumption of prey species by 12 piscivores
Time: 1977 - 1997
Spatial: Shelf wide
Contributed by: Overholtz
Figure B.40 (a-f)
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption estimation, see
Overholtz et al. (2000).
Key Points and Major Observations
Consumption of pelagic fishes and squids by the 12 predators varied
greatly during 1977-1997 and was particularly large in some years on
herring and sandlance. Predation on sand lance reached high levels in
the late 1970s and early 1980s, coincident with the large biomass of
this species present at the time and major declines in Atlantic mackerel
and herring. As the Atlantic mackerel stock began to recover, predation
on mackerel increased, reaching 89,000 mt in 1988. This was followed
by an increase in herring consumption to over 200,000 mt during 1992
and 1993, declining to about 100,000 mt in 1997. Consumption of short-finned
and long-finned squid averaged 24,000 and 46,000 mt during 1977-1997,
but remained relatively constant over this period. Predation on butterfish
was more variable than the other species, but with the exception of a
few years , was relatively low. The recent decline in consumption of
these species is directly related to declines in the biomass of key predators
such as spiny dogfish, cod, white hake, and bluefish. Earlier studies
(Bowman and Michaels 1984) suggest that these prey, especially sand lance,
herring and mackerel, were important in the diets of these key predatory
fish prior to 1977.
5. Snapshot of food web for three years
in three different decades
Time: 1977, 1987, and 1997
Spatial: Shelf wide
Contributed by: Link
Figures B.41, B.42, and B.43
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption estimation, see
Overholtz et al. (2000) and Link and Garrison (2002a).
Key Points and Major Observations
The size of the circle is proportional to the size of population; the
thickness of an arrow shows how much of the population is consumed by
predator. During1977, squid and sand lance were the major prey and this
was a relatively simple food web. During 1987 and 1997, this was a much
more complex food web, with the major groundfish populations lower in
abundance and the importance of pelagics as prey more notable.
6. Fish consumption and % fish in diet
of cod
Time: 1978 - 1997
Spatial: Shelf wide
Contributed by: Link
Figure B.44
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption estimation, see
Overholtz et al. (2000) and Link and Garrison (2002a).
Key Points and Major Observations
There was a peak in the early 1980s for both how much fish comprised
the diet of cod and how much fish biomass was consumed by cod. Lower
values in the 1990s likely reflect the smaller size structure of the
cod population.
7. Fish consumption by cod at age
Time: 1978 - 1997
Spatial: Shelf wide
Contributed by: Link
Figure B.45
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption estimation, see
Overholtz et al. (2000) and Link and Garrison (2002a).
Key Points and Major Observations
There is an overall decline in the amount of total fish consumed by
cod seen here and in Figure B.44. The amount of fish eaten by cod at
different ages varied over time. Through the 1980s and into the 1990s,
the relative and absolute amount of fish eaten by age 7+ cod declined.
In early to mid 1990s older fish (ages 7+) were a smaller component
of the population and contributed a relatively smaller proportion of
the amount of fish consumed relative to age 3-5 cod.
8. Cod % diet composition of major fish
prey
Time: 1973 - 1997
Spatial: Shelf wide
Contributed by: Link
Figure B.46
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For further details see Link and Garrison (2002b).
Key Points and Major Observations
This demonstrates the transfer of energy from pelagic to benthic environment.
It also seems to show prey switching based upon prey availability.
9. Spiny dogfish % diet composition of
major fish prey
Time: 1973 - 1997
Spatial: Shelf wide
Contributed by: Link
Figure B.47
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling.
Key Points and Major Observations
The dogfish diet seems to track prey availability. The diet of dogfish
is comprised mainly by pelagic prey.
10. Number of predators for sand lance,
herring, hermit crab, ophiuroids, mysids, and red hake
Time: 1973 - 1998
Spatial: Shelf wide
Contributed by: Link
Figure 48 (a-f)
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling.
Key Points and Major Observations
This metric is a measure of food web linkage density. There are some
notable changes over time, particularly an increase in red hake and herring
predators in more recent years.
11. Silver hake % cannibalism
Time: 1973 - 1998
Spatial: Shelf wide
Contributed by: Link
Figure B.49
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. These data represent what fraction of silver
hake diet consists of silver hake. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling.
Key Points and Major Observations
When other prey are not available, silver hake are cannabilistic. This
phenomena has a consistently high occurrence, with in an increasing trend
in the mid 1990s. How this impacts population dynamics is unclear.
12. Silver hake and red hake number of
prey items
Time: 1973 - 1998 (with 4 year moving averages overlaid)
Spatial: Shelf wide
Contributed by: Link
Figure B.50
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling.
Key Points and Major Observations
There was a decrease in the number of prey consumed by silver hake
in mid 1980s, with an increasing number of prey throughout the 1990s.
The number of prey of red hake has increased continuously until the mid
1990s. The two hakes show similar patterns and also exhibit similar diets.
13. Herring consumption to landings ratio
Time: 1977 - 1997
Spatial: Shelf wide
Contributed by: Overholtz
Figure B.51
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption and landings
information, see Overholtz et al. (2000).
Key Points and Major Observations
Consumption of Atlantic herring was below 50,000 mt from 1977-1987
and then increased in the 1990s to over 200,000 mt in some years. Landings
for this species averaged 82,000 mt during 1977-1997. As herring increased
in the 1990s, consumption to landings ratios increased dramatically in
the early 1990s and then declined. If predator fish biomass is allowed
to recover we would expect consumption of this species to increase and
greatly exceed landings in the future.
14. Mackerel consumption to landings ratio
Time: 1977 - 1997
Spatial: Shelf wide
Contributed by: Overholtz
Figure B.52
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption and landings
information, see Overholtz et al. (2000).
Key Points and Major Observations
Consumption and landings of Atlantic mackerel by 12 predatory fish
were fairly similar during 1977-1997 and both were well below established
reference points for this species (MSY 326,000 mt). Consumption to landings
ratios for this species were relatively constant during 1977-1997. This
suggests that a recovery in predator biomass may not cause any large
increases in consumption on this species, with the exception perhaps
of a large recruiting year-class. Several factors such as fast swimming
speed and enhanced growth rates, allowing for a larger body size, probably
make Atlantic mackerel less available or suitable to this suite of 12
predators.
15. Loligo consumption to landings
ratio
Time: 1977 - 1997
Spatial: Shelf wide
Contributed by: Overholtz
Figure B.53
Methodology and Data Source
These data are derived from both the NEFSC Bottom Trawl Survey Data
and the Food Habits Database. See Link and Almeida (2000) for further
details on the food habits sampling and Azarovitz (1981) for the bottom
trawl survey sampling. For specifics on the consumption and landings
information, see Overholtz et al. (2000).
Key Points and Major Observations
Consumption of long-finned squid exceeded landings and MSY (24,000
mt) in all years except 1993 and 1994. Consumption to landings ratios
for this species were relatively high throughout the 1977-1997 period,
averaging 2.36 and ranging from 0.58-4.88. This suggests that any increase
in predator biomass will translate into an immediate increase in consumption
of this species by predatory fish. Consumption will probably always be
in excess of sustainable landings for this species.
K. System Level Indices
We recognize that there are also several system level indices that
one could estimate to ascertain the status of this ecosystem. For example,
what are the values for emergy, exergy, free energy, information content,
energy flows, system level consumption, metabolism, and production, total
production, total biomass, and flux rates across time? Similarly, how
strong is the resilience, persistence, resistance, or stability of the
system? Not much is known in general or in a time series sense for these
measure, but these emergent metrics could be estimated in future efforts.
L. Summary of Biotic Metrics
We examined biotic metrics ranging from single species to ecosystem
level.
The early to mid 1980s seem to have a consistent "blip" in many of
the graphs. The cause of these peaks or troughs are currently unknown.
Some potential hypotheses include a change in the "environmental condition" (not
specified), removal of the foreign fishing fleets in 1976 and changes
in management during the late 1970s and early 1980s, predatory release
due to changes in overall selectivity, changes in the trophic linkages,
alteration of habitat, or some combination thereof.
Total biomass (as measured by the trawl survey time series) has been
remarkably consistent from the late 1960s to present given the large
changes observed in biomass of individual species.
Changes in the abundance and diversity of commercially important species
and associated bycatch species should be interpreted in light of changing
management measures over time. In particular, the implementation of the
closed areas since 1995 may influence these trends.
Are systematic (taxonomic) or trophic (functional) groupings more important
for providing information? Would plotting fishing pressure on graphs
of fish biomass improve our understanding? Similarly, would a similar
plot against environmental variables improve our understanding? These
and a suite of related questions merit examination in the future.
M. References
Azarovitz, T.R. 1981. A brief historical review of the Woods Hole Laboratory
trawl survey time series. In: Bottom Trawl Surveys. Doubleday
W.G., Rivard D. Canadian Special Publications in Fisheries and Aquatic
Sciences 58:62-67.
Brodziak, J. and Link, J. 2002. Ecosystem-based fishery management:
What is it and how can we do it? Bull. Mar. Sci. 70(2):589-611.
Benway, R.L. and Jossi, J.W. In Review. Ships of opportunity (SOOP)
sampling. In: Jossi, J.W. and C.A. Griswold (eds.) In Review. MARMAP
Ecosystem Monitoring: Operations Manual. NOAA Technical Memorandum NMFS-F/NEC.
CETAP. 1982. A characterization of marine mammals and turtles
in the mid- and north Atlantic areas of the U.S. outer continental shelf.
Cetacean and Turtle Assessment Program, University of Rhode Island. Final
Report, Contract AA51-C78-48, Bureau of Land Management, Washington,
DC, 538 pp.
Garrison, L.P. and Link, J. 2000. Dietary guild structure of the fish
community in the Northeast United States Continental Shelf Ecosystem.
Mar. Ecol. Prog. Ser. 202:231-240.
Gilbert, J.R. and Guldager, N. 1998. Status of harbor and gray seal
populations in northern New England. Final Report to: National Marine
fisheries Service, Northeast Fisheries Science Center, Woods Hole, MA.
Under NMFS/NER Cooperaative Agreement 14-16-009-1557. 13 pp.
Kane, J. 1993. Variability of zooplankton biomass and dominant species
abundance on Georges Bank, 1977-1986. Fish. Bull. 91:464-474.
Kane, J. 1999. Persistent spatial and temporal abundance patterns for
late-stage copepodites of Centropages typicus (Copepoda: Calanoida)
in the U.S. northeast continental shelf ecosystem. J. Plank. Res. 21(6):1043-1064.
Jossi, J.W., Benway, R.L., and Goulet, J.R. In Review. MARMAP Ecosystem
Monitoring: Program Description. NOAA Technical Memorandum NMFS-F/NEC.
Jossi, J.W. and Goulet, J.R. 1993. Zooplankton trends: US north-east
shelf ecosystem and adjacent regions differ from north-east Atlantic
and North Sea. ICES Journal of Marine Science, 50: 303-313.
Link, J.S. and Almeida, F.P. 2000. An overview and history of the food
web dynamics program of the Northeast Fisheries Science Center, Woods
Hole, Massachusetts. NOAA Technical Memorandum NMFS-NE-159.
Link, J.S. and Almeida, F.P. 2002. Opportunistic feeding of longhorn
sculpin: are scallop fishing discards an important food subsidy on Georges
Bank? Fish. Bull. 100:381-385.
Link, J.S. and Garrison, L.P. 2002a. Changes in piscivory associated
with fishing induced changes to the finfish community on Georges Bank.
Fish. Res. 55:71-86.
Link, J.S. and Garrison, L.P. 2002b. Trophic ecology of Atlantic cod Gadus
morhua on the northeast US continental shelf. Mar. Ecol. Prog.
Ser. 227:109-123.
Ludwig, J., and J. Reynolds. 1988. Statistical ecology. Wiley, New York.
337 p.
Meise, C.J. and Stehlik, L.L. In Press. Habitat use, temporal abundance
variability and diet of blue crabs from a New Jersey estuarine system.
Estuaries.
Mullin, K.D. In Review. Abundance and distribution of cetaceans in
the southern US Atlantic Ocean during summer 1998. Fish. Bull.
Murawski, S.I., Brown, R., Lin, H.L., Rago, P.J. and Hendrickson, L.
2000. Large-scale closed areas as a fishery-management tool in temperate
marine systems: The Georges Bank experience. Bull. Mar. Sci. 66:775-798.
NEFC (Northeast Fisheries Center). 1988. An evaluation of the bottom
trawl survey program of the Northeast Fisheries Science Center. NOAA
Technical Memorandum NMFS-F/NEC-52.
NEFSC (Northeast Fisheries Science Center). 1998a. Status of fishery
resources off the northeastern United States for 1998. NOAA Technical
Memorandum NMFS-NE-115.
Northeast Fisheries Science Center. 1998b. 26th Northeast
Regional Stock Assessment Workshop (26th SAW), Stock Assessment
Review Committee (SARC) consensus summary of assessments. National Marine
Fisheries Service, Northeast Fisheries Science, Center Reference Document
98-03. Woods Hole, Massachusetts.
Northeast Fisheries Science Center. 1998c. 27th Northeast
Regional Stock Assessment Workshop (27th SAW), Stock Assessment
Review Committee (SARC) consensus summary of assessments. National Marine
Fisheries Service, Northeast Fisheries Science, Center Reference Document
98-15. Woods Hole, Massachusetts.
Northeast Fisheries Science Center. 2000a. Assessment of 11 northeast
groundfish stocks through 1999. National Marine Fisheries Service, Northeast
Fisheries Science, Center Reference Document 00-05. Woods Hole, Massachusetts.
Northeast Fisheries Science Center. 2000b. 30th Northeast
Regional Stock Assessment Workshop (30th SAW), Stock Assessment
Review Committee (SARC) consensus summary of assessments. National Marine
Fisheries Service, Northeast Fisheries Science, Center Reference Document
00-03. Woods Hole, Massachusetts.
Northeast Fisheries Science Center. 2000c. 31st Northeast
Regional Stock Assessment Workshop (31st SAW), Stock Assessment
Review Committee (SARC) consensus summary of assessments. National Marine
Fisheries Service, Northeast Fisheries Science, Center Reference Document
00-15. Woods Hole, Massachusetts.
Northeast Fisheries Science Center. 2001. 32nd Northeast
Regional Stock Assessment Workshop (32nd SAW), Stock Assessment
Review Committee (SARC) consensus summary of assessments. National Marine
Fisheries Service, Northeast Fisheries Science, Center Reference Document
01-05. Woods Hole, Massachusetts.
O'Reilly, J.E. and Zetlin, C. 1998. Seasonal, horizontal, and vertical
distribution of phytoplankton chlorophyll-a in the northeast U.S. continental
shelf ecosystem. NOAA Technical Report NMFS, 139.
Overholtz, W.J., Link, J.S. and Suslowicz, L.E. 2000. Consumption of
important fish and squid by predatory fish in the northeastern USA shelf
ecosystem with some fishery comparisons. ICES Journal of Marine Science.
57:1147-1159.
Palka, D. 1995. Abundance estimate of the Gulf of Maine harbor porpoise.
pp. 27-50. In: A. Bjrrge and G.P. Donovan (eds.) Biology of
the Phocoenids. Rep. int Whal. Commn Special Issue 16.
Palka, D. 1996. Update on abundance of Gulf of Maine/Bay of
Fundy harbor porpoises. National Marine Fisheries Service, Northeast
Fisheries Science Center, Center Reference Document 96-04. Woods Hole,
Massachusetts.
Palka, D. 2000. Abundance of the Gulf of Maine/Bay of Fundy harbor
porpoise based on shipboard and aerial surveys during 1999.National Marine
Fisheries Service, Northeast Fisheries Science Center, Center Reference
Document 00-07. Woods Hole, Massachusetts.
Palka, D., Waring, G. and Potter, D. In review. Abundances of cetaceans
and sea turtles in the northwest Atlantic during summer 1995 and 1998.
Fish. Bull.
Pershing, A.J., Greene, C.H., Hannah, C., Mountain, D.G., Sameoto,
D., Head, E., Jossi, J.W., Benfield, M.C., Reid, P.C. and Durbin, E.G.
2001. Gulf of Maine/western Scotian Shelf ecosystems respond to changes
in ocean circulation associated with the North Atlantic Oscillation.
Oceanography, 14(3).
Sherman, K., Solow, A., Jossi, J., and Kane, J. (1998) Biodiversity
and abundance of the zooplankton of the Northeast Shelf Ecosystem. ICES
J. Mar. Sci. 55:730-738.
Smith, T., Palka, D. and Bisack, K.. 1993. Biological significance
of bycatch of harbor porpoise in the Gulf of Maine demersal gillnet fishery.National
Marine Fisheries Service, Northeast Fisheries Science Center, Center
Reference Document 93-23. Woods Hole, Massachusetts.
Stehlik, L.L. and Meise, C.J. 2000. Diet of winter flounder in a New
Jersey estuary: ontogenetic change and spatial variation. Estuaries 23:381-391.
Stoner, A.W., Manderson, J.P. and Pessutti, J.P. 2001. Spatially-explicit
analysis of habitat for juvenile winter flounder (Pseudopleuronectes
americanus): Combining generalized additive models and geographic
information systems. Mar. Ecol. Prog. Ser. 213:253-271.
Theroux, R.B. and Wigley, R.L. 1998. Quantitative composition and distribution
of the macrobenthic invertebrate fauna of the continental shelf ecosystems
of the northeastern United States. NOAA Technical Report NMFS, 140.
Waring, G.T., Quintal, J.M., and Swartz, S. (eds). 2000. U.S. Atlantic
and Gulf of Mexico marine mammal stock assessments - 2000. NOAA Technical
Memorandum NMFS-NE-162.
Table 4.1. Abundance estimates of marine mammals
and protected species in U.S. waters of the northwest Atlantic. (back
to Text)
| |
Year |
| Species |
1982 |
1991 |
1992 |
1995 |
1997 |
1998 |
1999 |
| Common dolphin |
4201 |
|
|
6743 |
|
30768 |
|
| Riss's dolphin |
11834 |
|
|
5050 |
|
29110 |
|
| Atl. Spotted dolphin |
2441 |
|
|
4772 |
|
36439 |
|
| Pantropical spotted dolphin |
|
|
|
4772 |
|
13117 |
|
| Bottlenose dolphin |
12069 |
|
|
13440 |
|
30633 |
|
| Striped dolphin |
16320 |
|
|
30935 |
|
61546 |
|
| White-sided dolphin |
38016 |
|
20400 |
27157 |
|
|
51640 |
| Harbor porpoise |
18934 |
37500 |
67500 |
74000 |
|
|
89700 |
| Pilot whale |
8839 |
|
|
8111 |
|
14524 |
|
| Beaked whales |
939 |
|
|
1516 |
|
3196 |
|
| Humpback whale |
|
|
|
|
|
|
816 |
| Sperm whale |
1301 |
|
|
2695 |
|
4702 |
|
| Fin/Sei whale |
6075 |
|
|
2229 |
|
|
2814 |
| Minke whale |
4945 |
|
2650 |
3810 |
|
|
2998 |
| Loggerhead turtles |
7702 |
|
|
4644 |
|
6010 |
|
| Leatherback turtles |
361 |
|
|
3136 |
|
1175 |
|
| Kemps Ridley turtle |
|
|
|
0 |
|
2260 |
|
| Harbor seal |
|
|
|
|
30990 |
|
|
V. HUMAN METRICS
(Click here for PDF Version)
A. Recreational Fishing
We recognize that recreational fishing is an important part of this
ecosystem. Although there is data available, no one from the group provided
data for this report. Certainly this is an important issue to consider
for some species, and merits further examination in the future.
B. Fishing Communities
What are the relevant communities of fishermen, what is the relation
of communities at sea to communities on land, what are the social relations
embodied in particular regional fishing practices? Are there appropriate
indices of communities, people, and cultures that can provide insight
into how this ecosystem functions and how the products and services and
of this ecosystem are used beyond economics? Are there indices for other
ecosystem goods and services?
Additionally, what about "anecdotal" or cultural environmental knowledge;
e.g., do fishermen's notions of space and environment coincide with scientific
ones? If not, what are the implications for management structures? What
environmental knowledge can/would fishermen contribute? What informal
rules for resource access and use would or do fishermen or groups of
fishermen regularly employ?
C. Commercial Fisheries
1. New England Otter Trawl Landings
Time: 1964-2000
Spatial: Shelf wide
Contributed by: Edwards
Figure H.1
Methodology and Data Source
These data are from the weighout database reported by dealers to NMFS.
Annual landings by species (live weight) were combined according to the
species managed by individual fishery management plans. Data are restricted
to U.S. bottom trawl vessels that landed in Maine, New Hampshire, Massachusetts,
or Rhode Island.
Key Points and Major Observations
New England otter trawl landings declined by two-thirds between 1964
and 2000. U.S. annual landings were higher before the Magnuson-Stevens
Fisheries Conservation and Management Act was implemented in 1977 (MSFCMA).
Landings peaked during the early 1980s after the MFCMA, but the overall
trend has been downwards since that time. The traditional targets of
otter trawl fishermen - i.e., Atlantic cod, haddock, yellowtail flounder
- have declined in absolute and relative importance from about 240 million
pounds or 44 percent of total trawl landings in 1964 to 36 million pounds
or 20 percent. Other species managed by the New England Council's Multispecies
Groundfish Plan have likewise declined in amount and importance. Otter
trawlers now also significantly target monkfish and skates.
2. New England Otter Trawl Revenues
Time: 1964-2000
Spatial: Shelf wide
Contributed by: Edwards
Figure H.2
Methodology and Data Source
These data are from the weighout database reported by dealers to NMFS.
Annual dockside revenues by species were combined according to the species
managed by individual fishery management plans. Data are restricted to
U.S. bottom trawl vessels that landed in Maine, New Hampshire, Massachusetts,
or Rhode Island. Revenues were adjusted to 2000-dollars using the GDP
implicit price deflator.
Key Points and Major Observations
Revenues were flat, averaging $150 million, until the New England fleet
expanded following the MSFCMA. Revenues peaked during the early1980s
at over $240 million and then declined to less than pre-MSFCMA levels
since about 1995, averaging $130 million. The absolute and relative importance
of the traditional target species declined from over $100 million and
60 percent during the mid-1960s to $24 million and less than 20 percent
during the mid 1990s. Revenues from cod, haddock, and yellowtail flounder
have since increased moderately. Despite a decline in landings, revenues
have been supported by increases in consumer demand (population of seafood
consumers and their income) which in turn increases dockside prices.
3. Total Number of Otter Trawl Vessels
Time: 1964-2000
Spatial: Shelf wide
Contributed by: Edwards
Figure H.3
Methodology and Data Source
These data are from the weighout database reported by dealers to NMFS.
Number of U.S. otter trawl vessels with landings reported in Maine, New
Hampshire, Massachusetts, or Rhode Island. Vessels are binned by tonnage
class (5-50 gross registered tons in ton class 2, 51-150 grt in TC3, >150
in TC4)
Key Points and Major Observations
The total number of otter trawl vessels increased gradually up to 1977,
particularly in TC3 and TC4. Vessel numbers increased quickly after the
MSFCMA into the early 1980s from about 600 to 1000. There were increases
in each vessel class. The total number of active otter trawl vessels
has vacillated around 750 during the 1990s.
4. Total Income of NE Otter Trawl Fisherman
(Profit)
Time: 1964-2000
Spatial: Shelf wide
Contributed by: Edwards
Figure H.4
Methodology and Data Source
These data are from the weighout database reported by dealers to NMFS.
and NMFS cost data. Annual dockside revenues by species were combined
according to the species managed by individual fishery management plans.
Data are restricted to U.S. bottom trawl vessels that landed in Maine,
New Hampshire, Massachusetts, or Rhode Island. Revenues were adjusted
to 2000-dollars using the GDP implicit price deflator. Costs (also adjusted
to 2000-dollars) are sample estimates from CMER (Cooperative Marine Education
and Research) survey projects by the University of Rhode Island. Costs
are for trip (e.g., fuel), repair and maintenance, and fixed (except
unknown loan and depreciation) expenses. See Lallemand et al. (1998,
1999) for further details.
Key Points and Major Observations
Results should be considered rough approximations due to incomplete
nature of cost data.
Total income vacillated around $80 million before the MSFCMA. Income
peaked during the late1970s/early1980s and then trended downwards until
1996. Income has improved since 1996, but at less than $60 million it
remains substantially below the pre-MSFCMA average. Income of crew averaged
40-50 percent of total income. Recent income is depressed relative to
revenues because of the costs of excess harvest capacity.
5.
Adjusted Average Income of NE Otter Trawl Fisherman
Time: 1964-2000
Spatial: Shelf wide
Contributed by: Edwards
Figure H.5
Methodology and Data Source
These data are from the weighout database reported by dealers to NMFS.
and NMFS cost data. Annual dockside revenues by species were combined
according to the species managed by individual fishery management plans.
Data are restricted to U.S. bottom trawl vessels that landed in Maine,
New Hampshire, Massachusetts, or Rhode Island. Revenues were adjusted
to 2000-dollars using the GDP implicit price deflator. Costs (also adjusted
to 2000-dollars) and crew size are sample estimates from CMER (Cooperative
Marine Education and Research) survey projects by the University of Rhode
Island. Costs are for trip (e.g., fuel), repair and maintenance, and
fixed (except unknown loan and depreciation) expenses. Income was averaged
over the number of vessels and approximate number of crew (2 crew in
TC2, 4 in TC3, 5 in TC4). See Lallemand et al. (1998, 1999) for further
details.
Key Points and Major Observations
Results should be considered rough approximations due to incomplete
nature of cost and crew data. Average income per vessel and crew fluctuated
considerably prior to the MSFCMA without trend. Average income trended
downward since the late 1970s to lows of $25,000 per vessel and $8,000
per crew in 1996. Average income for vessel owners and crew has improved
since 1996 but still remains below the pre-MSFCMA averages of about $80,000
and $20,000, respectively.
6.
Standardized fishing effort on Georges Bank
Time: 1960-1987
Spatial: Georges Bank
Contributed by: Brodziak
Figure H.6
Methodology and Data Source The multispecies and multifleet
catch and effort data are reported to NAFO, standardized to account for
differences in effective fishing effort using information on vessel size,
gear, and country of origin using a general linear modeling approach.
See Mayo et al. (1992) and Brodziak and Link (2002) for further details.
Key Points and Major Observations
Fishing effort was very high during the mid 1960s to mid 1970s when
foreign distant water fleets were (over)harvesting fish on Georges Bank.
Fishing effort declined by about 2/3 after passage of the Magnuson Stevens
Fishery Conservation Act of 1976. This act extended the USAs Exclusive
Economic Zone (EEZ) to include Georges Bank. Domestic fishing effort
increased from 1977-1987, although this increase was moderate compared
to the increase in distant water fleet effort in the 1960s.
7. Standardized catch-per-unit effort (CPUE)
for Georges Bank fisheries
Time: 1960-1987
Spatial: GB
Contributed by: Brodziak
Figure H.7
Methodology and Data Source
Multispecies and multifleet catch and effort data reported to NAFO
were used to compute standardized CPUE based on differences in vessel
size, gear, and country of origin using a general linear model estimation
approach. See Mayo et al. (1992) and Brodziak and Link (2002) for further
details.
Key Points and Major Observations
Standardized CPUE declined from the early 1960s to mid 1970s as fish
stocks were depleted. There was a short-term increase in CPUE after passage
of the Magnuson Act in the late 1970s followed by a sharp decline through
the mid 1980s. Fishery CPUE is not expected to be proportional to aggregate
fish stock biomass. Instead, CPUE is likely a nonlinear function of fish
biomass. In this context, the observed declines in CPUE are expected
to underestimate the actual declines in fish stock biomass on Georges
Bank.
8. Fishery harvest rate in relation to
spawning biomass for Georges Bank haddock
Time: Composite picture, 1931-1998
Spatial: Georges Bank
Contributed by: Brodziak
Figure H.8
Methodology and Data Source
Under the current management approach, a target and a threshold harvest
rate have been determined for Georges Bank haddock. The target and threshold
depend on the current spawning biomass. The graph shows the observed
fishing mortality and spawning biomass from an assessment of the Georges
Bank haddock stock in relation to the target and threshold harvest rate
lines. See Brodziak and Link (2002) for further details.
Key Points and Major Observations
Harvest rates on the Georges Bank haddock stock have generally exceeded
target rates during 1931-98. Thus, management measures have generally
not been effective to ensure that the harvest rate has been near its
target for this stock. Spawning stock biomass of Georges Bank haddock
has begun to increase as harvest rates have been reduced in the 1990s.
The 1998 data point shows the status of the spawning biomass is still
well below target spawning biomass.
9.
Georges Bank cod, haddock and yellowtail flounder yields
Time: 1935 - 2000
Spatial: Georges Bank
Contributed by: Brodziak
Figure H.9
Methodology and Data
Source
Time series of total fishery
landings for Georges Bank cod, haddock, and yellowtail flounder stocks
were gathered from historical databases. These figures do not include
discarded catches. See Brodziak and Link (2002) for further details.
Key Points and Major
Observations
Yields were high during
the 1930s-1950s, peaked in the 1960s, declined in the 1970s, peaked
again in the early 1980s, and then declined. Georges Bank cod, haddock,
and yellowtail yields have increased moderately in recent years after
reaching record lows in the mid 1990s. Landings of the three primary
groundfish stocks on Georges Bank have been below the estimated long-term
potential yield (LTPY) for most of the observed time series. One causal
factor leading to the lack of achievement of the long-term potential
yield from these three primary stocks has been chronic overfishing,
e.g., fishermen catching fish faster than the stocks can replenish
themselves.
10.
Fishing Activity, by state (North)
Time: 1999
Spatial: Shelf wide
Contributed by: Olson
Figure
H.10
Methodology and Data
Source
These data were derived
from the 1999 logbook
dataset. Latitude-longitude
coordinates from converted loran observations were used to locate fishing
activity by state in various regions of the shelf. Coordinates were
truncated to two decimal points for visual display. Only New England
and upper Mid-Atlantic are displayed.
Key Points and Major
Observations
Fishing-activity
is in terms of both a proxy for total days/location (total days absent,
except fractions thereof for trips recording multiple locations) summed
over all commercial trips and vessels (size of dots) and by state of
landing (color of
dots). Coastal areas
are dominated by their respective states, but there is considerably
more mixing in more distant waters. What
then is the relation between "community" and "territory"? Are there
different kinds of communities? Are there kinds of informal management
regimes operant in some of these territories-of-use? Different
places show different practices: why, what different kinds of social
relations are enabled in these different ways of fishing, and with
what different kinds of implications?
11.
Fishing Activity, by state (South)
Time: 1999
Spatial: Shelf wide
Contributed by: Olson
Figure
H.11
Methodology and Data
Source
These data were derived
from the 1999 logbook
dataset. Latitude-longitude
coordinates from converted loran observations were used to locate fishing
activity by state in various regions of the shelf. Coordinates were
truncated to two decimal points for visual display. Only Mid-Atlantic
waters are displayed.
Key Points and Major
Observations
Fishing-activity
is in terms of both a proxy for total days/location (total days absent,
except fractions thereof for trips recording multiple locations) summed
over all commercial trips and vessels (size of dots) and by state of
landing (color of
dots). Coastal areas
are dominated by their respective states, but there is considerably
more mixing in more distant waters. What
then is the relation between "community" and "territory"? Are there
different kinds of communities? Are there kinds of informal management
regimes operant in some of these territories-of-use? Different
places show different practices: why, what different kinds of social
relations are enabled in these different ways of fishing, and with
what different kinds of implications?
12.
Summer Flounder Catch
Time: 1999
Spatial: Shelf wide
Contributed by: Olson
Figure
H.12
Methodology and Data
Source
These data were derived
from the 1999 logbook
dataset. Latitude-longitude
coordinates from converted loran observations were used to locate fishing
activity by state in various regions of the shelf. Coordinates were
truncated to two decimal points for visual display. Only Mid-Atlantic
waters are displayed.Key Points and Major Observations
Fishing-activity
is in terms of both a proxy for total days/location (total days absent,
except fractions thereof for trips recording multiple locations) summed
over all commercial trips and vessels that caught at least 300 pounds
fluke. The size of the pie chart was determined by size of the total
fluke catch, the color of the pie chart slices was determined by state
of landing, and the size of the slice was determined by that state's
total days at that location. This is a single-species representation. How
does the management system in place (here, quotas by state of landing)
affect the spatiality of fishing-are the bands of activity on fishing
grounds by state of landing more clear-cut than the previous figures?
If so, to what extent is that attributable to the management, to the
bio-ecosystemic properties of fluke, and to fishing practices of fluke
fishermen (Who is targeting fluke and who are generalists? Questions
of seasonality, "community" and "territory" emerge again.)
13.
New England landed value, by county
Time: 1994-2000
Spatial: Shelf wide
Contributed by: Olson
Figure
H.13
Methodology and Data
Source
These data are from dealer
weigh-out records, including all vessels landing in New England counties,
1994-2000. The landed
value is summed across all species by county of landing, joined with
census county maps.
Key Points and Major
Observations
Coupled with next figure
(H.14), these data seem to show an "uneven" spatiality to temporal
changes in fishing. Although changes in the number of vessels were
similar over all counties, changes in landed value were not. Are there
changes in landing practices, changes in social/spatial relations,
etc.? An answer would require additional ethnographic research, as
well as knowledge of other regional differences in fishing practices
(targeted species, if any; type of fleet; etc.).
14.
New England number of permitted vessels, by county
Time: 1997-2001
Spatial: Shelf wide
Contributed by: Olson
Figure
H.14
Methodology and Data
Source
These data are from permit
data, 1997-2001 (application years). Distinct vessel numbers were counted
and summed by homeport county, for New England only.
Key Points and Major
Observations
Coupled with previous figure
(H.13), these data seem to show an "uneven" spatiality to temporal
changes in fishing. Although changes in the number of vessels were
similar over all counties, changes in landed value were not. Are there
changes in landing practices, changes in social/spatial relations,
etc.? An answer would require additional ethnographic research, as
well as knowledge of other regional differences in fishing practices
(targeted species, if any; type of fleet; etc.).
15.
Average days absent
Time: 1999
Spatial: Shelf wide
Contributed by: Olson
Figure
H.15
Methodology and Data
Source
These data were derived
from the 1999 logbook
dataset. Latitude-longitude
coordinates from converted loran observations were used to locate fishing
activity by state in various regions of the shelf. Coordinates were
truncated to two decimal points for visual display. New
England and Mid-Atlantic areas are displayed. All
trips were summed by truncated locations; crew size averaged over trips
at that location (not vessels). Does not account for "popularity" of
sites.
Key Points and Major
Observations
This graphical summary provides
another way of displaying qualitative differences in use of fishing
space, in terms of reading heterogeneity into fishing practices. Coastal
waters are, unsurprisingly, dominated by day-trippers; trips in offshore
waters vary in length. This
isn't related solely or simply to biomass. Day-boat fishing is not
practiced simply because the fish are close by and may as well be caught
first, but because fishing as a day-boat is a social practice that
is valued because of the other sorts of relations it enables (e.g.
family, community on land etc.). If so, and especially in an "ecosystem-based
fishery management" context, the effect of qualitative factors on ecosystem
processes should also be considered.
16.
Groundfish Landings
Time: 1995-2000
Spatial: Shelf wide
Contributed by: Olson
Figures
H.16 and H.17
Methodology and Data
Source
These data were derived
from the 1995-2000 logbook dataset. The quantity kept of groundfish
was summed by statistical area. Groundfish included: Atlantic cod,
winter flounder, witch flounder, yellowtail flounder, American plaice,
haddock, white hake, redfish, pollock, red hake, ocean pout, silver
hake, monkfish, cusk, and wolffish
Key Points and Major
Observations
These data show the temporal and spatial
distribution of groundfish catches.
To what extent do
these variations correspond to species abundances, and to what extent
do they correspond with social practices (as in previous graphs)?
17.
Pelagic Landings
Time: 1995-2000
Spatial: Shelf wide
Contributed by: Olson
Figures
H.18 and H.19
Methodology and Data
Source
These data were derived
from the 1995-2000 logbook dataset. The quantity kept of pelagic species
was summed by statistical area. Pelagics included: bluefish, butterfish,
Atlantic herring, Atlantic mackerel, and menhaden.
Key Points and Major
Observations
These data show the temporal and spatial
distribution of groundfish catches.
To what extent do
these variations correspond to species abundances, and to what extent
do they correspond with social practices (as in previous graphs)?
18.
Bigeye Tuna Landings and Value
Time: 1993-1997
Spatial: Atlantic
Contributed by: Link
Figure
H.20
Methodology and Data
Source
These data were obtained
from NMFS "Status of the Stocks" indicating the total value and biomass
of tuna landed. See NMFS (1999) for further details.
Key Points and Major
Observations
Although a short time series,
there is a decline in recent years. This represents information from
large, apex predators.
19.
Atlantic Cod Landings and Value
Time: 1993-1997
Spatial: Atlantic
Contributed by: Link
Figure
H.21
Methodology and Data
Source
These data were obtained
from NMFS "Status of the Stocks" indicating the total value and biomass
of cod landed. See NMFS (1999) and NEFSC (1998) for further details.
Key Points and Major
Observations
Although a short time series,
there is a decline in recent years. This represents information from
a culturally, ecologically, and economically important species in this
ecosystem.
20.
Swordfish Landings and Value
Time: 1993-1997
Spatial: Atlantic
Contributed by: Link
Figure
H.22
Methodology and Data
Source
These data were obtained
from NMFS "Status of the Stocks" indicating the total value and biomass
of tuna landed. See NMFS (1999) and NEFSC (1998) for further details.
Key Points and Major
Observations
Although a short time series,
there is a decline in recent years. This represents information from
large, apex predators.
D.
Fisheries Management (Governance)
1.
Fraction of Georges Bank closed year-round to fishing
Time: 1977-2000
Spatial: Georges Bank
Contributed by: Brodziak
Figure
H.23
Methodology and Data
Source
Several large areas of Georges
Bank were closed year-round to fishing in 1995 to help conserve and
rebuild depleted groundfish stocks. Fishing vessels can transit through
these areas but cannot fish there. See Brodziak and Link (2002) for
further details.
Key Points and Major
Observations
Over 25% of Georges Bank
was closed to fishing in the mid 1990s. Prior to these closures, some
areas were closed on a seasonal basis.
2.
Minimum mesh size regulations for trawl fishing nets
Time: 1977-2000
Spatial: Northeast
USA shelf fisheries
Contributed by: Brodziak
Figure
H.24
Methodology and Data
Source
Minimum trawl mesh sizes
for large-mesh otter trawl fisheries have been adjusted since 1977
to help to conserve groundfish under the New England Fishery Management
Multispecies Fishery Management Plan. See Brodziak and Link (2002)
for further details.
Key Points and Major
Observations
Minimum mesh sizes were
increased in 1983 and 1994 to help conserve groundfish. Larger mesh
sizes retain fewer small, unmarketable fish in the codend of the trawl
net. Thus, a larger minimum mesh leads to less bycatch of juvenile
fishes.
3.
Days-at-sea restrictions for groundfish vessels
Time: 1977-2000
Spatial: Northeast
USA groundfish fisheries
Contributed by: Brodziak
Figure
H.25
Methodology and Data
Source
The total number of days
a fishing vessel can spend at sea were regulated in 1996 for the purpose
of reducing fishing effort directed at depleted New England groundfish
stocks. This effort regulation applies to New England groundfish fisheries.
See Brodziak and Link (2002) for further details.
Key Points and Major
Observations
Prior to 1996, there was
no restriction on the number of days domestic fishing vessels could
be fishing. Some large vessels received more than 120 days at sea based
on their fishing history - the graph shows the default allocation that
most vessels received.
E. Summary
of Human Metrics
There has been a clear change
in the effort, landings, and profit of the fishing fleet over the past
four decades. Major events include a shift in targeted species, a decline
in the poundage and value of landings, and an increase in the number
of vessels after the late 1970s. This corresponds to the passage and
implementation of the MSFCMA. Landings of two apex predators and Atlantic
cod in more recent years show, although short term, a similar decline
during the 1990s, perhaps due to changes in regulation of these species.
The patterns of spatial
allocation of fishing effort and landings are logical given the logistic
and cultural constraints in the region. Although these maps are relatively
short time-series, historical data may be available to extend this
analysis back for approximately 30 years. What is the role of other
non-fishing sources of income in the decision-making process of whether
to fish?
Regulations on the fisheries
have become increasingly restrictive in recent years, with changes
in closed areas, mesh size, and days at sea all much less lenient than
in the 1960s and 1970s.
F.
References
Brodziak, J. and
Link, J. 2002. Ecosystem-based fishery management: What is it and how
can we do it? Bull. Mar. Sci. 70(2):589-611.
Lallemand, P., Gates, J.M.,
Dirlam, J. and Cho, J-H. 1998. The cost of small trawlers in the Northeast.
Final Report, Cooperative Marine Education and Research Program, Department
of Environmental and Natural Resource Economics, University of Rhode
Island.
Lallemand, P., Gates, J.M.,
Dirlam, J. and Cho, J-H. 1999. The cost of large trawlers in the Northeast.
Final Report, Cooperative Marine Education and Research Program, Department
of Environmental and Natural Resource Economics, University of Rhode
Island.
Mayo, R., M. Fogarty, and
F. Serchuk. 1992. Aggregate fish biomass and yield on Georges Bank,
1960-87. J. Northw. Atl. Fish. Sci. 14:59-78.
NEFSC 1998. Status of the
Fishery Resources off the Northeastern United States. NOAA Technical
Memorandum NMFS-NE-115.
NMFS. 1999. Fisheries of
the United States, 1998. Current Fishery Statistics No. 9800.
VI. Integration
(Click here for PDF Version)
A. Similar Patterns, Key Observations
Substantial changes in the ecosystem occurred in the late1970s to early
1980s. Change was apparent across several abiotic, biotic, and human
metrics. Many metrics had a notable increase or decline during this period.
Of the 123 metrics we examined with long enough time series, 44 exhibited
an increase during this period. Additionally, 39 exhibited a decline
during the same time. Thus, over 67.5% of the metrics we examined suggest
that some event or series of events occurred in the late 1970s and early
1980s. The synchronicity of these changes also reflects the interaction
among the various metrics. We explore what may have caused the changes
and how the changes might be related in the next chapter. Here we want
to document similar patterns among the various types of metrics.
B. Abiotic Metrics
Environmental conditions have varied through time.
Over a decadal time scale, there have been some moderate changes in
water temperatures. The 1960s had cooler water conditions than the 1970s
and 1980s, while the 1990s was somewhat warmer than preceding decades.
It is uncertain if there is a relationship between these observed temperatures
and the NAO. The offshore waters of Georges Bank and the open Gulf of
Maine do not exhibit the same temperature trend as coastal waters. Within
the Mid-Atlantic Bight, water masses shifted during the 1990s. There
was less slope water in the Mid-Atlantic Bight in the 1990s with warmer
and less saline water conditions. In the 1990s, there was also more Scotian
Shelf water in the Gulf of Maine, but the effects of this cooler water
may have been offset by more coastal warming so that no trend in temperature
was apparent. How these changes affected the biota remains a major question.
Some short-term cycling in temperature anomalies is apparent, on the
time scale of 3-5 years. However, there is no appearance of a major regime
shift in oceanographic conditions such as have been documented in the
late 1970s in the northeastern Pacific Ocean. Overall, the observed oceanographic
metrics suggest the system is undergoing natural variation about its
long-term (40 year) average conditions, with some moderate serial correlation.
C. Biotic Metrics
The composition of the biotic community has changed across different
levels of organization, from zooplankton to forage fish to top predators.
Phytoplankton abundance (as measured by standing biomass of chlorophyll a on
the offshore shelf) has remained relatively constant through time. This
suggests that primary productivity in this ecosystem is relatively stable.
Two caveats are that the composition of species may have changed and
that the productivity is not measured by chlorophyll a.
Predatory release on the zooplankton community was not apparent when
planktivore abundance was severely reduced by fishing. The implication
of this observation is that the zooplankton community is primary regulated
by bottom-up environmental forcing. In particular, given the substantial
changes in the abundance of Atlantic herring and Atlantic mackerel, the
primary pelagics, one would have expected the zooplankton community to
increase substantially as these predators were less abundant.
It is unknown whether the benthic community has changed due to a lack
of time series data. This gap in our knowledge may be important to fill
and there is some ongoing research by the NEFSC directed at alleviating
this gap.
The composition of the fish community has changed dramatically through
time. Groundfish abundance declined dramatically under intensive harvest
pressure. Squid, which are preyed upon by groundfish, increased in abundance
during the 1970s as groundfish abundance declined. Similarly, American
lobster catches increased following the decline in groundfish abundance.
While groundfish declined, abundances of elasmobranchs, including spiny
dogfish and skates, increased. Elasmobranch abundance began to decline
in the 1990s, however, as fishery harvests increased from negligible
to substantial levels, especially for large adult female spiny dogfish.
The abundance of primary pelagics, Atlantic mackerel and Atlantic herring,
declined substantially in the 1970s. In recent years, the abundance of
primary pelagics has increased substantially as harvests and abundances
of some predators have remained low.
D. Human Metrics
Revenues generated by the otter trawl fleet in New England, the primary
component of the multispecies groundfish fishery, have declined through
time. Otter trawl revenues peaked in the early 1980s and have declined
since then. This long-term decline has occurred as the number of groundfish
vessels has increased. Part of the increase in groundfish vessels was
a federal government program to loan money to build more vessels following
implementation of the Magnuson-Stevens Fisheries Conservation and Management
Act (FCMA) of 1976. The impact of declining revenues and increasing vessel
numbers is that this fishery is producing a smaller benefit stream and
that these benefits are being divided among a larger set of participants.
Overall, this would suggest that there may be less satisfaction within
this fishery sector in recent years as profitability has been reduced,
on average.
In a similar context, the composition of the landings of the otter
trawl fleet in New England has changed dramatically through time. The
increase in landings of non-groundfish species corresponds to the decrease
in groundfish abundance. The behavior of the otter trawl fleet, as a
top predator within the system, has changed in relation to the availability
of various fishery resources. One potentially dangerous aspect of this
type of behavior is that species groups may be serially depleted as the
fishing fleet moves to target more abundant groups after others have
been depleted. In the long term, this type of behavior is not likely
to be sustainable and could result in substantial and possibly irreversible
changes to the species composition of the ecosystem.
Information on the standardized fishery catch-per-unit effort (CPUE)
data from the foreign and domestic fleets on Georges Bank during the
1960-1980s shows that capture decreased over threefold as aggregate fishery
resource abundance declined. Such a decrease in efficiency would be expected
based on bioeconomic theory for an open-access resource - this is another
indication that the top-down impact of human predation on the system
has been substantial. The decline in CPUE is similar to the declining
trend in groundfish abundance. The declining trends in the two metrics
are not identical because fishery CPUE is not likely directly proportional
to abundance and is difficult to standardize when fishing practices and
fishing gear have changed through time.
The harvest control rule for the Georges Bank haddock stock suggests
that this productive resource has been chronically overfished since the
1930s. The long term impact of overfishing on Georges Bank haddock has
led to a severe decline in haddock abundance. Although some rebuilding
of this stock has occurred in recent years under restrictive management,
Georges Bank haddock abundance is still well below target abundance.
It seems likely that other groundfish species, for example Atlantic cod,
have experienced similar long-term exploitation patterns although long-term
assessment data are not available to directly support this point.
Fishing regulations on the New England otter trawl fleet, the primary
component of the groundfish fishery, have increased since the implementation
of the Magnuson-Stevens FCMA of 1976. One apparent result of increased
regulation has been a reduction in the landings and fishing mortality
on groundfishes. These decreases may have helped to foster some rebuilding
of the groundfish resources. However, despite recent increases in abundance,
many groundfish are less abundant than during the early 1960s, immediately
prior to the intensive harvests by the foreign distant water fleets.
The behavior of the groundfish fishing fleet in recent years shows
that human predators exhibit spatial heterogeneity in their fishing behavior.
Cultural and socioeconomic differences exist within the fleet at the
port, county, and state level and there are some obvious spatial patterns
in choice of fishing location and movements among fishing areas. Some
of the reasons why certain choices are made can be related directly to
regulatory and political-econonic regimes, but others require further
study.
One question raised by the decline in otter trawl revenues in recent
years, is "Why are fishermen still choosing to fish when the economic
returns are so poor?" For fisherman who consider their livelihood not
simply a job but a way of life, cultural aspects of the traditional fishing
communities provide other important rationales to continue to participate
in the fishing fleets. Changes in fishing practices and fishing communities,
such as diversification to target non-groundfish resources, have probably
contributed to sustaining the fishing fleet while target species abundances
have declined and regulations have increased.
E. Summary
We have observed changes in the biotic, abiotic, and human components
of the Northeast U.S. Continental Shelf ecosystem over the past forty
years. Despite these changes, the relative constancy of aggregate biomasses
across trophic levels (e.g., phytoplankton, zooplankton, fish groups,
etc.) over the time series is surprising and suggests that aggregate
system biomass is resilient to perturbations applied to date. This suggests
that human activities thus far have not severely eroded the productive
capacity of the system in terms of bottom-up forcing. Yet the species
composition at any given trophic level has changed dramatically. The
changes that have been observed may be attributable to both top-down
forcing (e.g., through fishing) as well as inherent natural variation
(bottom-up) in ecosystem processes.
VII. Synthesis
(Click here for PDF Version)
A. Heurism, Relationships, and Generated Hypotheses
Even though we know a lot about many aspects of this ecosystem, we
do not fully understand all of the processes and mechanisms that have
generated the range of conditions we have observed in this ecosystem.
The challenge remains for us as scientists to understand ecosystem function
and structure.
The working group listed some of the more important questions related
to our understanding of this ecosystem. We list this set of questions
and either answer them based on the data presented in this document or
recommend research to address them. In many respects, these questions
represent some of the key hypotheses of how this ecosystem is structured
and functions.
B. Principal Question
What are the natural and anthropogenic factors underlying change
(or variability) in the northeast U.S. continental shelf ecosystem
and its subsystems?
We may never be able to quantify all of the processes in this ecosystem.
Even partially addressing this question will be helpful to our understanding
of this ecosystem.
C. Major Questions
1. System
What are the important changes in biota, oceanography, and fisheries
through our time period of observation, by subsystem or finer scale
as needed (subsystem-see below)?
We have documented changes in the ecosystem over our period of observation;
see the previous chapter for a more detailed description of these changes.
Many of these represent an order of magnitude (or more) of change. That
we can ascertain the status of an ecosystem such as this one is not trivial.
Has there been a change in relative energy flux through pelagic
and demersal fish populations through time - a trophic regime shift
(by subsystem)?
Yes. The system is now "horizontal" (dominated by pelagic species that
migrate) rather than "vertical" (demersal species with higher site affinity)
and the biomass, energy fluxes, and community structures reflect this
(see Figure 3 in Link 1999).
What are the sources of temporal and spatial variation in fish and
marine mammals in the system due to climate change, bottom-up forcing
(temperature, habitat loss/degradation inshore, impacts of toxic chemicals
inshore, and nutrients), trophic cascades (impacts of selective predation
by fish/marine mammals, prey refugia, and fisheries harvesting), etc.?
Certainly these are all important potential forcing functions. At this
time it is difficult to clearly determine the relative contribution of
each source of variability to the overall variability of the biotic community.
Future multivariate analyses will need to partition this variance.
What are the potential consequences of a regime-shift between a
demersal fish/benthos- dominated ecosystem to a pelagic fish/plankton-dominated
system?
We're not sure anyone knows the full ramifications of this type of shift.
Certainly there are a few hypothesized outcomes (e.g., slower recovery
of groundfish, predation on demersal fish larvae by pelagic planktivores,
removal of energy off the shelf or to different parts of the shelf, increased
competition among different components of the system, increased ctenophore
predation, etc.), but those remain to be tested.
What are the relative strengths of couplings within and between
benthic and pelagic systems? How would this vary by oceanographic region
(Gulf of Maine, Georges Bank, Mid Atlantic Bight, etc.)? How strongly
are regions linked? (What would we be leaving out when we go to smaller/higher
resolution models?)
We do not know the relative strength of pelagic versus benthic subsystem
couplings, but in general, the system appears to be loosely coupled.
Is there a characteristic predictability/stochasticity of dynamics
for each region/component? (How reasonable is "deterministic" management?)
It is difficult to say because of the multiple and simultaneous processes
occurring in this ecosystem. We think a standard signal (i.e., pattern)
may be generally detectable for key processes. Yet being able to predict
specific components of this ecosystem, and evaluating their associated
stochasticity, remains difficult.
What are the relative effects of environment vs. fishery on ecosystem/community/population
structure and dynamics? (How should we modify current population dynamics
models used in assessments to reflect this?)
It is fairly clear that in general, the dominant factor influencing
fish populations is fishing. The environment is then a key second forcing
function that can determine the recovery trajectory. The environment
also can strongly dictate the level of productivity of the system or
community or a population.
2. Abiotic
Is there evidence of an oceanographic regime shift on a system-wide
scale, or by subsystem?
The evidence is unclear. Some metrics show an increased warming in recent
times and a change in the NAO, yet the high amount variability and closer
examination suggest that the major physical processes acting in the Northeast
U.S. Continental Shelf ecosystem are generally the same ones (albeit
at slightly different times or magnitudes).
Are there trends in offshore, nearshore, and estuarine habitat quality?
What indicators of quality exist for the last few decades, and is there
any way to extrapolate back a few more decades?
We are unlikely to have the data to answer these questions. Examining
sediment cores along transects may be one feasible approach to address
this issue.
Is there any spatial/temporal coupling of physical environment and
seasonal migrations of biota between estuaries, coastal waters, continental
shelf, and continental slope?
We do not know if we have the data to answer the question for couplings
and migrations between estuaries and nearshore to the offshore waters.
Along the continental shelf and slope, data exists to describe seasonal
migrations of various biota. These patterns have been documented elsewhere
(e.g., Grosslein and Azarovitz 1982; Bowman et al. 1987; Overholtz et
al. 1991).
What are the potential consequences of nitrogen enrichment (from
the atmosphere and land use activities in coastal watersheds) of estuaries
and coastal waters on the food chains supporting fish/marine mammals
and as a source for harmful algal blooms (HABs)?
We do not know the answer to these questions. Satellite imagery and
nutrient monitoring would help to better address these issues.
How is fishery performance affected by environmental factors (human
behavior, fish behavior/availability)?
In a general sense, the weather greatly influences fish and fisher distribution.
In a more specific sense, it is uncertain how the environment influences
catch rates.
What is the verdict on environmental change in the Georges Bank
ecosystem; is it stable or changing?
It is both stable and changing, depending upon the scale of observation
and the particular environmental metric examined. Again, some metrics
show an increased warming in recent times and a change in the NAO, yet
the high amount variability and closer examination suggest that the major
physical processes acting in the northwest Atlantic are generally consistent
(albeit at slightly different times or magnitudes).
3. Biotic
What appear to be the dominant top-down and bottom-up effects in
the food chain, by subsystem?
Regardless of spatial consideration, fishing is the dominant top-down
effect. This effect may or may not propagate through lower trophic levels.
Predation is a less dominant top-down effect in this ecosystem. It is
unclear to what degree physics, nutrient input, etc., influence lower
trophic levels as bottom-up effects. The physical conditions may create
local conditions that alter the magnitude of species and fisheries interactions,
which may indirectly affect those lower trophic levels.
What appear to be the relative importances of top-down and bottom-up
effects on commercial fish and invertebrate recruitment strengths through
time?
Fishing is a very strong effect, but environmental conditions are also
important. Allocating importance in terms of proportional influence remains
to be done. Recruitment remains a particularly difficult issue.
What are the impacts of increasing pinniped populations on fish/endangered
species (i.e., Atlantic salmon; sturgeons; etc.) and potential interactions
with fixed gear and aquaculture?
We don't have the data to answer this question at this time.
Are production and net production stable or changing over time in
the Georges Bank ecosystem?
The standing biomass of the full ecosystem and sub-components of it
(e.g., phytoplankton, zooplankton, various guilds, etc.; c.f., Figures
B.7-B13, B.27a-l; O'Reilly and Zetlin (1998)) appear to be roughly constant
over time. However, the particular species composition in any one of
these groups has changed across time. Thus, the productivity of the different
groups and the entire ecosystem is not readily known at this time.
Are zooplankton numbers per m3 stable or changing over
time in the Georges Bank ecosystem?
They appear to be roughly consistent across time, albeit with notable
changes in species composition and variation (c.f., Figures B.7-B.13).
4. Human
Do ecosystem-level analogues to single species reference points
exist? What about control rules?
There are most likely ecosystem-level analogues. The suite of metrics
described in previous chapters are promising possibilities to include
in decision criteria models and analyses.
How have anthropogenetic influences other than fishing affected
the status of the ecosystem? For example, can changes in the ecosystem
be related to pollution? Or, what levels of pollution would be required
to have a detectable impact on the ecosystem?
We do not know at this time.
Can ecosystem status be projected? Can current and projected ecosystem
status improve management advice from single species stock assessments
and forecasts? For example, recruitment of species X is expected to
increase/decrease in future due to changes in temperature, phytoplankton,
food web, increase/decrease in species Y, etc. Can the same be done
for fishery management reference points as well?
We think that this certainly can be done, but it remains to be demonstrated
in the current management and science institutional context.
Can we offer guidance regarding placement and timing of closed areas
that goes beyond a particular commercially important species? That
is, how will predictions of ecosystem level impacts of different management
measures such as closed areas, mesh size changes, species targeting,
etc., influence management strategies?
We think that this certainly can be done, but it remains to be demonstrated
beyond generalities.
Is there some utility of closed areas for groundfish as a fishery
management tool and as a means for increasing biodiversity/fish productivity,
both inside and outside of the closed areas? Similarly, what
is the role of Marine Protected Areas (MPAs) as a fishery management
tool?
Yes. We do not directly present the type of information to answer these
questions in the previous chapters (but see figures H.23, B.1-B.4, B.23,
B.24) and refer the reader to Murawski et al. (2000) and Brown et al.
(1998).
What are the tradeoffs between optimum fisheries harvesting approaches
and maximizing the "net economic return" to the nation from the use
of these public resources?
The specifics are uncertain, but in general and based upon first principles
we would probably be trading short-term maximization of profit with long-term
profit and resource sustainability. Much further work remains to adequately
address this issue.
What is the role of socioeconomic forces on the harvesting behavior
of commercial and recreational fishers and how do these relate to effective
fisheries management strategies?
This is an area in which
we have little data. Certainly the broad study of values and valuation
would shed some insight into this question, particularly why fishers
and fishing communities attempt to persist in an often unprofitable
activity.
What is the combined
economic value of the commercial stocks (not landed value)? Is it
consistent with the long-term notion of sustainability? If not (probably
not), what is the magnitude of economic waste each year (these questions/issues
involve "green accounting")?
These are difficult questions
to address.
What are the implications
of systems thinking (e.g., biological and technical interactions)
for single-species management and Maximum Sustainable Yield (MSY)?
Is there a better systems concept, such as resource portfolios, for
fisheries management?
The implications are that
some management advice may need to be qualitatively adjusted or modified,
probably to be more conservative. Certainly different approaches would
be useful to help understand an ecosystem, and we advocate as holistic
an examination of the ecosystem as possible, but can not necessarily
espouse one approach over any other at this time. Quantitative approaches
to alter single species reference points and targets remain a large
and fruitful area of research.
What are the design characteristics
and functions of an institutional arrangement that could employ ecosystem-based
management of fishery (and other marine) resources? How do these
compare to the current Council/NMFS management arrangement?
It is not likely that we
will know the answer to this for some time. Changes to the SFA/MSFCMA
may force us to reexamine our institutions. Accounting for other laws
(e.g., MMPA, ESA, NEPA, etc.) may also contribute to this reexamination.
Comparisons to other regions and countries may be an useful first step
to address this question.
Have major fishing episodes
(i.e., ICNAF, recent USA) permanently altered the ecosystem?
Certainly they have altered
parts of the ecosystem. To what extent these changes are "permanent" or
irreversible is unknown. A formal stability and steady state analysis
would be required to address this question more rigorously.
D. Summary
and Conclusions
Although integrating and
synthesizing the information from a diverse set of disciplines is a
difficult task, there is value in inter-disciplinary working groups.
We would encourage the expansion of this approach to include the perspectives
from other disciplines working on marine ecosystems.
It takes substantial and
multiple time series of metrics and associated monitoring to assess
the status of a system. No one metric best described the status of
the ecosystem, even though many of the metrics demonstrated similar
trends and many of the metrics similarly captured the directionality
of key processes and relationships. It is clear that several of these
metrics should be examined concurrently. Examining just one or a few
may be misleading. This work is distinct from those that focus on a
single process in that it integrates all these considerations at once.
If one uses the leading indicators of any national economy as an analogy,
a similar approach is useful for indexing the status of an ecosystem.
The change observed for
many of the metrics during the late 1970s and early 1980s corresponds
to the passage of the first Magnuson-Stevens Fisheries Conservation
and Management Act in the late 1970s, which resulted in the expansion
of the domestic fleet and a subsequent increase in groundfish landings
beyond sustainable levels. Changes in the physics of the ecosystem
were also occurring during that period. These two considerations, along
with their derivatives (e.g., habitat alteration, changes in competitive
balance among species, temperature induced migrations, recruitment
success, switching targeted species, etc.), were probably the causal
(at least initially) events that led to the observed changes (and lags
thereof) in the observed ecosystem metrics.
From this work we have developed
a unique compilation and understanding of trends, magnitudes, and relationships
among key processes. The knowledge from this study is highly heuristic
and as such inherently valuable. We recommend regularly assessing the
status of ecosystems at appropriate time scales and reference points,
analogous to single species fish stock assessments.
E. Acknowledgments
We thank all the members
of the NEFSC's in-house Ecosystem Status Working Group (ESWG) who have
contributed in various fashions to the development of this and related
products. In particular, along with the contributors to this document
we acknowledge W. Gabriel, S. Murawski, J. Boreman, R. Reid, T. Noji,
G. Reppucci, D. Packer, B. Rountree and J. Quinlan for their encouragement,
stimulating comments, and general participation in the working group.
We are indebted to J. Brodziak and K. Lang who helped compile most
of the graphics into a standard format. We thank D. Dow who provided
an earlier draft abstract, S. MacLean and D. Mountain for compiling
the group discussion in Chapter. 3, C. Legault and W. Overholtz for
compiling the group discussion in Chapter. 4, and J. Olson and S. Edwards
for compiling the group discussion in Chapter. 5. We thank C. Griswold
and W. Gabriel for their excellent editorial suggestions on formatting
and wording of prior versions of this manuscript. This is the first
of what we hope are many products from the ESWG.
F.
References
Bowman,
R.E., Azarovitz, T.R., Howard, E.S. and Hayden, B.P. 1987. Food and
Distribution of Juveniles of Seventeen Northwest Atlantic Fish Species.
NOAA Technical Memorandum NEC-45.
Brown,
R.W., Sheehan, D. and Figuerido, B. 1998. Response of cod and haddock
populations to area closures on Georges Bank. ICES CM 1998/U:9.
Grosslein, M.D. and Azarovitz,
T.R. 1982. Fish distribution. Mesa New York Bight Atlas Mono. 15. NY
Sea Grant Institute.
Link, J. 1999. (Re)Constructing
Food Webs and Managing Fisheries.
Proceedings of the 16th Lowell Wakefield Fisheries Symposium-
Ecosystem Considerations in Fisheries Management. AK-SG-99-01: 571-588.
Murawski, SA, Brown, R,
Lai, H-L, Rago, PJ, and Hendrickson, L. 2000. Large-scale closed areas
as a fishery-management tool in temperate marine systems: The Georges
Bank experience.
Bull. Mar. Sci. 66:775-798.
Overholtz,
W.J., Armstrong, R.S., Mountain, D.G., and Terceiro, M. 1991. Factors
Influencing Spring Distribution, Availability, and Recreational Catch
of Atlantic Mackerel (Scomber scombrus) in the Middle Atlantic and
Southern New England Regions. NOAA Technical Memorandum NEC-85.
O'Reilly,
J.E. and Zetlin, C. Seasonal,
horizontal, and vertical distribution of phytoplankton chlorophyll
a in the northeast U.S. continental shelf ecosystem. NOAA Technical
Report NMFS, 139.
