Northeast Fisheries Science Center Reference Document 06-06
A Historical Perspective on the Abundance
and Biomass of Northeast Demersal
Complex Stocks
from NMFS and Massachusetts Inshore Bottom
Trawl
Surveys, 1963-2002
by by Katherine A. Sosebee1 and Steven X. Cadrin2
1National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods
Hole, MA 02543
2Massachusetts Division of Marine
Fisheries (Current address: School
for Marine Science & Technology, 706 South Rodney
French Blvd, New Bedford , MA
02744)
Print
publication date April 2006;
web version posted April 20, 2006
Citation: Sosebee KA, Cadrin SX. 2006. A historical perspective on the abundance and biomass of
Northeast complex stocks from NMFS and Massachusetts inshore bottom trawl surveys, 1963-2002. US Dep Commer, Northeast Fish Sci Cent Ref Doc. 06-05; 200 p.
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ABSTRACT: Temporal
and spatial patterns in biomass and abundance of 16 species of groundfish
and four groups of groundfish species during 1963-2002 were determined
using data from annual spring and autumn research vessel bottom trawl
surveys conducted by the Northeast Fisheries Science Center (NEFSC)
and the Massachusetts Department of Marine Fisheries (MADMF). Maps
were created depicting abundance distributions, within five-year periods,
for each species and species group. General temporal trends in
abundance and biomass were modeled with regression analysis. The
results indicate varying degrees of spatial change in distribution,
and a general decline in overall groundfish abundance through 2002.
INTRODUCTION
The northeast demersal groundfish complex was defined by
the Northern Demersal Subcommittee of the Northeast Regional Stock Assessment
Workshop as a group of sixteen species inhabiting the northeast
United States continental shelf (NEFSC 1996). The group comprises:
(a) ten species regulated under the Northeast Multispecies Fishery Management
Plan: Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus),
pollock (Pollachius virens), Acadian redfish (Sebastes fasciatus),
white hake (Urophycis tenuis), yellowtail flounder (Limanda
ferruginea), American plaice (Hippoglossoides platessoides),
witch flounder (Glyptocephalus cynoglossus), winter flounder (Pseudopleuronectes americanus),
and windowpane flounder (Scophthalmus aquosus; NEFMC 1993); (b)
three species exploited by small mesh fisheries: silver hake (Merluccius
bilinearis), red hake (Urophycis chuss), and ocean pout (Macrozoarces
americanus); and (c) three additional species often caught by the
northeast demersal fishery: Atlantic wolffish (Anarhichas lupus),
goosefish, (Lophius americanus) and cusk (Brosme brosme). In
1995, a request was made by the Steering Committee of the Stock Assessment
Workshop for the 21st Stock Assessment Review Committee to
investigate the distribution of these species (NEFSC 1996). Several
analytical techniques including Generalized Additive Models (O’Brien
1997), habitat preference (Helser and Brodziak 1996), and Lorenz
Curve (Wigley 1996) methods were used at this time to examine the changes
in distribution for some of the species. This report provides a
retrospective analysis of indices of abundance and biomass through 2002
for 25 individual stocks and 12 aggregate groups from Northeast Fisheries
Science Center (NEFSC) and Massachusetts Division of Marine Fisheries
(MADMF) research vessel bottom trawl surveys but is not intended to replace
individual stock assessments. A simple examination of temporal
and spatial trends in the distribution of species comprising the complex
is also presented.
METHODS
Stock
Indices and Distribution
NEFSC
offshore research vessel bottom trawl surveys have been conducted annually
in the autumn since 1963 (offshore strata 61-76 started in 1967), and
in the spring since 1968 (Azarovitz 1981). Inshore stations (< 27
m; 15 fm) from Southern New England to Cape Hatteras were added to the
surveys beginning in autumn 1972, and then added in the Gulf of Maine
beginning in spring 1979. Sampling is based on a stratified random
design using area and depth zones (Figure 1, Figure 2, Figure 3 and Figure 4). Between
300 and 600 stations are sampled in each survey, with the number of stations
allocated to each stratum in proportion to stratum area. Standard
tows are 30 minutes in duration, at a towing speed of approximately 3.8
knots.
Several gear changes have occurred since the start of the NEFSC surveys
(NEFSC 1991). In 1985, "Portuguese polyvalent" doors replaced the
"BMV" oval doors used since 1963. Three vessels have
conducted the survey (Albatross IV, Delaware II and Atlantic
Twin). The
standard sampling gear used in the surveys has been the "#36 Yankee"
trawl , except during the spring from 1973 through 1981 when a "#41 Yankee" trawl
was used. Conversion factors for these gear changes have been calculated
for some species (NEFSC 1991; Sissenwine and Bowman 1978). The Atlantic
Twin surveyed the inshore areas from autumn 1972 to spring 1975,
but no conversion factors have been calculated for this vessel.
Massachusetts inshore spring and autumn bottom trawl surveys, conducted
by the Massachusetts Division of Marine Fisheries, were initiated in
1978 (Howe 1989). Sampling is based on a stratified random design
using five geographic regions and six depth strata (Figure
5). In
each seasonal survey, approximately 100 sampling stations are allocated
and assigned in proportion to the stratum area. Standard tows are
20 minutes in duration at a speed of 2.5 knots. The sampling gear
is a 3/4 North Atlantic type two seam ('whiting') otter trawl. Two
vessels have conducted the survey (Francis Elizabeth, 1978-1981; Gloria
Michelle, 1982-Present) but no conversion factors are available.
For each stock, indices of relative biomass (stratified mean weight
per tow) and abundance (stratified mean number per tow) were calculated
for each of the surveys (Cochran 1977). Strata sets, transformations,
and gear conversions used for each stock are listed in Table
1. Distribution
maps of abundance were developed for each species for five-year periods. The
depth contours on each map represent 60 m (33 fathoms), 90 m (50 fm),
180 m (100 fm) and 900 m (500 fm). The 60 m contour was not digitized
east and north of Cape Cod and is not plotted in this region.
Aggregate Indices and Distribution
Abundance and biomass indices were calculated for four aggregate groups
of species: principal groundfish (Atlantic cod, haddock, pollock, Acadian
redfish, and white hake), principal flounders (yellowtail flounder, American
plaice, witch flounder, winter flounder, and windowpane flounder), small-mesh
groundfish (silver hake, red hake, and ocean pout), and other groundfish
(Atlantic wolffish, goosefish, and cusk). The indices were calculated
for three areas: Gulf of Maine (Offshore Strata 26-30,36-40), Georges
Bank (Offshore Strata 13-25), and Southern New England (Offshore Strata
1-12) for both seasons of the NEFSC survey. Indices were also calculated
for these groups for the entire Massachusetts survey area for both seasons. Distribution
maps (in five-year blocks) were generated for each species group using
data from both the NEFSC and the Massachusetts trawl surveys.
Trend Analyses
General temporal trends in survey indices of abundance and biomass
were modeled with regression analysis. The rate of change in a
stock was assumed to be an exponential process:
Nt =
Nt-1 er (1)
where abundance (N) at time t is a function of abundance in the previous
year and the exponential rate of change (r). The parameter r is
a composite rate incorporating recruitment, somatic growth (for biomass),
natural mortality and fishing mortality (and perhaps emigration and immigration). When r equals
zero, the stock size remains constant, because mortality and growth (including
recruitment) are in balance. When r is negative the stock
declines (mortality exceeds growth and recruitment) and when r is
positive the stock increases (growth and recruitment exceed mortality). The
same process can be assumed for an index of abundance (n):
nt =
nt-1 er (2)
A value of r was estimated for each survey time series
(autumn NEFSC; spring NEFSC; autumn Massachusetts; spring Massachusetts)
with simple loglinear regression:
nt =
no e rt + ε (3)
or
Ln(nt)
= Ln(no) + rt +ε (4)
where an abundance index observation is a loglinear function of the
predicted index level at the start of the series (no), the
exponential rate of change over t years, and a lognormally distributed
observation error (ε). As this simple model assumes that r is
constant over the survey time series, episodes of recruitment and mortality
are integrated over the time series.
RESULTS AND DISCUSSION
Stock Indices and Distribution
Spring
and autumn NEFSC survey abundance and biomass indices from 1963-2002
are presented in Appendix A (Figures A1-A10). Abundance
and biomass indices from the spring and autumn Massachusetts surveys,
1978-2002, are presented in Appendix B (Figures
B1-B6). Species
distributions in the NEFSC surveys are presented in Appendix
C (Figures
C1-21), and distributions in MADMF surveys are presented in Appendix
D (Figures D1-D20). Station
locations in these NEFSC and MADMF surveys are depicted in the first
set of figures of Sections C and D.
Indices of biomass and abundance for Gulf of Maine cod in the NEFSC spring and autumn surveys declined from
the early 1980s to the early 1990s after a ten-year period of fluctuating
catches (Figure A1; Mayo 1998; Mayo et al. 2002b). NEFSC
survey indices of Gulf of Maine cod in 1997 remained at or near record-low
levels but increased through 2002. The very large 2002 autumn survey
index was due primarily to one large tow (Mayo and Terceiro, 2005). The
distribution map of cod in the Gulf of Maine shows high catches in inshore
waters (around and inshore of the 50 fathom contour), particularly since
1979 when the survey first began to sample these habitats (Figure
C2). The
most recent survey time block (1998-2002) shows the highest concentrations
of Gulf of Maine cod are found in inshore waters while low catches occur
in the deeper waters of the central Gulf of Maine (Figure
C2d). Biomass
indices of cod from the MADMF spring survey declined throughout the entire
time series despite large survey catches in 1989 and 1990 (Figure
B1). The
large indices recorded in the spring of 1999 through 2001 surveys were
due mainly to the 1998 year class (Mayo and Terceiro 2005). The
majority of Gulf of Maine cod sampled by the inshore survey were caught
in Massachusetts Bay at stations greater than 15 m (8 fm) deep (Figure
D2).
Georges Bank cod indices of abundance and biomass in the NEFSC
spring and autumn surveys declined steadily from the 1970s to the 1990s
after an initial increase in the late 1960s (Figure
A1; O'Brien 1998;
O'Brien and Munroe 2001). Abundance and biomass indices of Georges
Bank cod from NEFSC surveys in spring 2002 and autumn 2001 remained at
or near record-low levels. The large 2002 survey values were caused primarily
by a few large tows (Mayo and Terceiro 2005). The decline in abundance
can also be seen in the distribution of cod on Georges Bank (Figure
C2)
both in the autumn and in the spring. By the autumn period from
1993-1997, cod were not present in the central portion of the northern
edge and in Southern New England, and the remaining were concentrated
on the Northeast Peak and in the Great South Channel. This pattern
remained in place for the 1998-2002 time period as well. Cod are
distributed in shallower waters on Georges Bank in the spring than in
the autumn. Cod are found in the deeper waters of the northern
edge of Georges Bank in the autumn.
Abundance and biomass indices for Gulf of Maine haddock from
the NEFSC autumn and spring surveys followed similar trends, with a sharp
decline in the 1960s followed by a smaller peak in the late 1970s (NEFC
1986; NEFSC 2001a; Figure A1). A steady decrease then occurred, and both
abundance and biomass fluctuated at extremely low levels from the mid-1980s
to near historic lows in 1997. Increases in both biomass and abundance
indices occurred from 1997-2002 in the spring and through 2000 in the
autumn (Mayo and Terceiro 2005). The decline and subsequent increase
in haddock abundance in the Gulf of Maine can also be seen in the distribution
plots based on NEFSC surveys, particularly between the 90 m (50 fm) and
180 m (100 fm) depth contours (Figure C3). All MADMF indices of
haddock abundance and biomass decreased through 1997 and then increased,
similar to the NEFSC survey indices (Figure B1). MADMF inshore
autumn catch rates of Gulf of Maine haddock have been used to indicate
year class strength because the survey is able to detect differences
in cohort strength (NEFC 1986). Although haddock were caught in
very low numbers from 1983 to 1997, the 1998 year class was apparently
detected (NEFSC 2001a).
Georges Bank haddock indices of abundance and biomass declined
rapidly from very high levels supported by large year classes from the
early to mid-1960s, increased in the 1970s following recruitment of large
year classes, but remained low through the mid-1990s (Figure
A1; Brown
and Munroe 2000). Indices increased slightly through 1997 but remained
well below historic levels. The increase in the value of the spring
index in 1996 was due to a single large tow in an area that had been
closed to fishing since December 1994. Further increases in the
survey indices occurred through 2002 as the above average 1998 year class
recruited to the survey and was protected by the closed areas (Mayo and
Terceiro 2005). Haddock appeared to have concentrated on the Northeast
peak and in the Great South Channel from the early 1980s through 2002
(Figure C3).
The NEFSC pollock biomass and abundance indices declined steadily
following a peak in the mid-1970s (Figure A2; Mayo and Terceiro 2005)
and remained among the lowest values detected through 1997. The
spring survey indices remained low but highly variable through 2002 while
the autumn survey indices increased steadily. Pollock were found
in greatest numbers in Massachusetts Bay, the edges of Georges Bank,
the Great South Channel and the Scotian Shelf (Figure
C4). Pollock
were generally found in the shallows of Georges Bank in slightly higher
numbers in the spring than in the autumn (Figure
C4). The decline
in abundance indices over the time series can be seen in the increased
proportion of tows with zero pollock catch, mostly in the Gulf of Maine. Pollock
have been sampled in all but two MADMF autumn surveys (Figure
B1). The
majority of pollock caught by the MADMF survey were in Massachusetts
Bay in the spring (Figure D4).
The NEFSC biomass and abundance indices for Acadian redfish declined
steadily from 1963 through 1982 (Figure A2; Mayo 1993; Mayo et al. 2002a). From
1982 through 1995 there was a slight increasing trend. In 1996,
the availability of redfish to the survey gear in the autumn appeared
to have changed abruptly and the abundance indices increased to a new
maximum value. The 1997 spring survey was dominated by one very
large tow (the largest in the time series). The increase in survey
abundance and biomass indices continued through 2002 and appears to have
been caused by an increased survival of year classes produced in the
1980s (Mayo and Terceiro 2005). These changes are evident also
in the distribution maps for both the spring and the autumn (Figure
C5). MADMF
redfish indices have fluctuated without trend (Figure
B1), but appear
to detect relatively abundant year classes. The inshore survey may not
adequately sample redfish for stock assessment purposes because they
were not present in ten spring surveys and seven autumn surveys. The
Massachusetts survey catches some redfish in deep waters of Massachusetts
Bay (Figure D5).
Spring and autumn indices of biomass and abundance for white hake in
the NEFSC survey increased in the 1960s and fluctuated without trend
throughout the 1970s (Figure A2; NEFSC 1995; Sosebee et al. 1998;
NEFSC 1998; NEFSC 2001b). The indices then fluctuated without trend
at a slightly lower level than in the 1970s during the remainder of the
time series. Since the early 1990s, the indices declined and were
at or near record low levels in 1997. The survey indices increased
slightly through 2002 due to a large 1998 year class (Mayo and Terceiro
2005). White hake are caught in shallower waters in the autumn,
when juveniles are found in inshore areas (Figure
C6). In the spring,
white hake are located in deeper waters of the Gulf of Maine and off
the southern slope of Georges Bank (Figure C6). All MADMF white
hake abundance and biomass indices decreased during the time series (Figure
B2). Most white hake caught by the Massachusetts survey were in
Cape Cod and Massachusetts Bays in the autumn (Figure
D6).
Georges Bank yellowtail flounder indices of biomass and abundance
exhibited a steady decline from the beginning of the time series (Figure
A3; Cadrin 1997; Cadrin et al. 2000) in the NEFSC survey. Biomass
and abundance indices increased temporarily in 1980 and 1981, fluctuated
in the late 1980s and early 1990s, and increased rapidly through 2001-2002
(Mayo and Terceiro 2005). The decrease in abundance is shown in
the distribution maps for both seasons (Figure
C7), and the increased
survey catches in recent years are primarily from the eastern portion
of Georges Bank (Figure C7d).
Southern New England – Mid-Atlantic yellowtail flounder NEFSC
survey indices fluctuated without trend throughout the 1960s but declined
precipitously in the early 1970s (Cadrin 2003; Figure
A3). An increase
occurred in the late 1970s and early 1980s, but the indices again decreased
and remained relatively low for the rest of the time period, except for
a small increase due to the 1987 year class. Yellowtail flounder
became concentrated around the 60 m (33 fm) contour in southern New England
as abundance declined (Figure C7). Spring MADMF abundance indices
declined (Figure B2) although SNE yellowtail flounder are rarely caught
by the MADMF survey (Figure D7), and were absent in several years.
NEFSC abundance and biomass indices of Cape Cod – Gulf of
Maine yellowtail flounder (Cadrin and King 2003) fluctuated at
low levels throughout the 1980s and 1990s (Figure
A3). The spring
survey indices increased through 2000 while the autumn survey indices
remained variable. MADMF spring biomass and abundance indices of Cape
Cod yellowtail decreased from 1978 through 1986, but remained relatively
constant between 1987 and 2002 (Figure B2). Yellowtail flounder
in the Cape Cod group are generally caught at stations greater than
30 m (17 fm) deep by the MADMF inshore survey (Figure
D7).
American plaice NEFSC survey indices of abundance and biomass
declined from the 1960s through the early 1970s (Figure
A3; O'Brien et
al. 1992; O'Brien and Esteves 2001). A period of high relative
abundance followed until the early 1980s when abundance again began to
decline. This decline continued throughout the 1980s, reaching a low
in 1987. Since that time there has been a generally increasing
trend in both indices (Mayo and Terceiro 2005). Concentrations
of American plaice can be found around the 90 m (50 fm) contour in the
NEFSC surveys (Figure C8). Spring MADMF inshore indices fluctuated
without trend throughout the time-series (Figure
B2). Autumn MADMF
indices increased from 1987 through 1991 then slightly decreased (Figure
B2). American plaice are most frequently caught by the MADMF survey
at stations greater than 60m (33 fm) deep (Figure
D8).
Witch flounder indices of biomass and abundance have been variable,
exhibiting an overall declining trend throughout most of the NEFSC survey
time series (Figure A4; NEFSC 1994; Wigley and Mayo 1994; Wigley et
al. 1999; Wigley et al. 2003) and reaching a record low in
the late 1980s. Both abundance and biomass indices remained low
until very recently, with increased abundance in the last five years. Witch
flounder are found primarily at depths exceeding 90 m (50 fm) in the
NEFSC surveys (Figure C9). All MADMF biomass and abundance indices
decreased (Figure B3). Most witch flounder sampled by the inshore
survey in the Gulf of Maine are caught in Massachusetts Bay at stations
greater than 40 m (22 fm) deep (Figure D9).
Gulf of Maine winter flounder biomass and abundance indices
decreased in both the spring and autumn NEFSC surveys from 1981 to the
early 1990s (Figure A4; NEFSC 2003). While these indices have since
fluctuated, an overall decrease in biomass is evident until the last
few years (Mayo and Terceiro 2005). The majority of winter flounder
caught in the NEFSC survey are found in waters less than 90 m (50 fm;
Figure C10). MADMF spring biomass decreased through the mid-1980s
and gradually increased through 2000 (Figure B3). Winter flounder catches
in the Gulf of Maine are distributed throughout the range covered by
the MADMF inshore survey (Figure D10).
Georges Bank winter flounder abundance and biomass indices from
the NEFSC survey fluctuated without trend until the late 1970s when biomass
began to steadily decline while abundance continued to fluctuate in response
to apparent variability in recruitment (Figure
A4; Brown et al. 2000;
NEFSC 2002a). Both indices reached record lows in 1991 but had
increased through 2002 (Mayo and Terceiro 2005). Winter flounder
occur on the shallowest parts of Georges Bank (Figure
C10).
Southern New England-Mid-Atlantic winter flounder biomass and
abundance indices decreased in the 1960s to a low in the early 1970s
in the NEFSC survey (Figure A4; Shepherd et al. 1996; NEFSC 1999;
NEFSC 2003). A short period of increase in the survey indices followed
until 1980 when there was a rapid decline in both indices. Since
that time, indices fluctuated without trend through 1996 at or near record-low
levels, increasing in 1997. The autumn survey continued to increase
through 2002 (Mayo and Terceiro 2005). Most winter flounder in
the southern New England and Mid-Atlantic area are caught in waters less
than 60 m (33 fm) deep (Figure C10). MADMF inshore spring indices of
abundance and biomass declined throughout the 1980s, increasing after
1991 (Figure B3; NEFSC 1999). Most winter flounder in this area
are caught at stations greater than 20 m (11 fm) deep in MADMF surveys
(Figure D10).
Gulf of Maine – Georges Bank windowpane flounder indices
of biomass and abundance from the NEFSC surveys increased during the
early part of the time series to the early 1970s (Figure
A5; NEFSC 1993;
NEFSC 1998; NEFSC 2002b). Subsequently, all indices fluctuated
without trend until the mid-1980s, when a steady decline began to occur. In
the mid-to-late 1990s, an increase in the survey indices occurred (Mayo
and Terceiro 2005). The majority of windowpane flounder in this
stock unit occur on Georges Bank proper with some fish also caught in
shallower portions of the Gulf of Maine (Figure
C11). There appears
to be a seasonal shift in distribution, with fish found in deeper waters
off the southern flank of Georges Bank in the spring and on top of the
Bank in the autumn.
Southern New England – Mid-Atlantic windowpane flounder indices
of abundance and biomass from the NEFSC survey decreased through the
mid-1990s, then remained relatively low through 1997 with a slight increase
through 2000 (Figure A5; NEFSC 1993; NEFSC 1998; Mayo and Terceiro 2005). Indices
through 2002 were among the lowest on record. This decline in abundance
in the NEFSC survey is shown in the distribution maps for this stock
by both fewer fish caught per tow and fewer tows with any windowpane
flounder (Figure C11). Most windowpane are now caught in inshore
areas less than 60 m (33 fm).
The MADMF indices of biomass and abundance for windowpane flounder
for the entire Massachusetts survey area decreased steadily between 1982
and 1991, increased through 1997, and again declined through 2002 (Figure
B3). The majority of windowpane flounder sampled by the inshore
survey are caught in the spring, at stations less than 30 m (17 fm) deep
(Figure D11).
Gulf of Maine – Northern Georges Bank silver hake indices
of biomass and abundance declined sharply in the early 1960s, but then
generally increased since the late 1960s (Figure
A6; NEFSC 2006). This
increase in abundance can be seen in the relative accumulation of data
points in the Gulf of Maine over time (Figure
C12).
Southern Georges Bank – Mid-Atlantic silver hake indices
decreased in the early part of the time series then fluctuated without
trend. (Figure A6; NEFSC 2006). The decline in abundance can be
seen in the distribution maps for the southern New England area in particular
(Figure C12).
MADMF inshore biomass and abundance indices for silver hake have fluctuated
without trend (Figure B4). Most silver hake sampled by the Massachusetts
survey are caught at stations greater than 20 m (11 fm) deep in spring
and throughout the Gulf of Maine in autumn (Figure
D12).
The trend in the Gulf of Maine – Northern Georges Bank red
hake survey indices resembles that of the northern stock of silver
hake indices (Figure A6; Sosebee 2005). Most red hake are caught
between 60 m (33 fm) and 180 m (100 fm) in the NEFSC survey (Figure
C13).
Southern Georges Bank – Mid-Atlantic red hake indices
also followed a pattern similar to the southern stock of silver hake
(Figure A6; Sosebee 2005). Following a decline in abundance and
biomass indices in the 1960s, the 1970s represented a period of relative
stability as both biomass and abundance indices fluctuated without trend. In
the mid-1980s, a slight decline occurred and the indices are now fluctuating
without trend at a lower level. This lower level of abundance is
also shown in the distribution maps for the late 1980s and 1990s in the
reduction of both numbers of fish and number of positive tows (Figure
C13).
MADMF spring indices of biomass and abundance for red hake decreased
(Figure B4). The majority of red hake sampled by the inshore survey
are caught at stations greater than 20 m (11 fm) deep in spring and greater
than 30 m (17 fm) deep in autumn (Figure D13).
Spring NEFSC biomass and abundance indices of ocean pout declined
in the early part of the time-series until the mid-1970s, when a sharp
increase occurred (Figure A7; NEFC 1990; NEFSC 1998; NEFSC 2002b). In
the mid-1980s, however, a decline began that continued through 1997,
with stable catches following through 2002 (Mayo and Terceiro 2005). The
seasonal difference in the catchability of ocean pout is evident in the
distribution maps (Figure C14). The decline in abundance is also
evident as ocean pout have concentrated around the 60 m (33 fm) depth
contour, particularly in autumn. MADMF abundance indices from spring
surveys also decreased from the early 1980s through 1997 (Figure B4). Most
ocean pout in the Massachusetts survey are caught in the spring, predominantly
in Cape Cod and Massachusetts Bays, at depths greater than 30 m (17 fm;
Figure D14).
Atlantic wolffish NEFSC abundance and biomass indices fluctuated
without trend until the 1980s, when they decreased precipitously and
remained at or near record-low levels through 2002 (Figure
A7; NEFSC
1998). Wolffish appeared to be concentrated between the 90 m (50 fm)
and 180 m (100 fm) depth contours in the NEFSC surveys (Figure
C15). MADMF
spring biomass and abundance indices are more variable but indicate the
same sharp decline (Figure B5). There have been 6 spring surveys
and 17 autumn surveys which have not caught any wolffish. In the
latest 5-year time block, only one wolffish was caught in the spring,
and no wolffish were caught in the autumn. The Massachusetts survey caught
wolffish primarily in the spring in deep waters of Massachusetts Bay
(Figure D15).
NEFSC goosefish abundance indices fluctuated without trend throughout
most of the time series while there has been an overall decline in biomass
indices (Figure A7, NEFSC 1992; NEFSC 2002a). In the autumn survey,
biomass has remained low while abundance has increased, signifying a
decline in the mean weight of the stock. Changes in distribution
have occurred over the time series with declines notably occurring in
the Southern New England area in waters between 90 m (50 fm) and 180
m (100 fm) (Figure C16). The recent increases in abundance are
due primarily to increased recruitment in the Gulf of Maine region. All
MADMF biomass and abundance indices decreased, except for autumn abundance,
which increased (Figure B5). Goosefish are caught in almost all Massachusetts
survey strata in spring, and most are caught at stations greater than
30 m (17 fm) deep in autumn (Figure D16).
NEFSC indices of biomass and abundance for cusk fluctuated greatly,
but these indices have steadily declined since 1985, and all indices
remained at or near record-low levels through 2002 (Figure
A7; NEFSC
1998). Cusk have been primarily distributed in deeper water in
the central portion of the Gulf of Maine (Figure
C17). The steady decline
is also evident in the distribution maps, with very few fish caught in
1993-1997 and 1998-2002. Only one cusk was caught in the 25-year
MADMF inshore survey.
Aggregate Indices
Gulf of Maine
Principal groundfish biomass and abundance indices from the
NEFSC surveys declined steadily over the time series in both spring and
autumn (Figure A8). These indices were dominated mostly by haddock
and redfish at the start of the time series; by pollock, cod and white
hake during the 1970s; and by white hake followed by redfish in the later
part of the time series. As a result of the shift in species composition
from cod and haddock to white hake, and, to a lesser extent, redfish
during the 1980s, the aggregate biomass index for this group had stabilized
at a record-low level and the aggregate abundance index increased slightly
through 1995. The increases in both survey indices from 1996-2002
were due primarily to the influx of redfish and the large tow of cod
in the 2002 autumn survey. The change in abundance is reflected in the
distribution maps with lower catches in the Gulf of Maine in 1993-1997,
followed by increase in 1998-2002 (Figure C18).
The Gulf of Maine principal flounder indices of abundance and
biomass (Figure A8), dominated by American plaice and witch flounder,
decreased in the early 1960s and increased in the 1970s. All indices
declined sharply in the early 1980s, and the biomass indices remained
relatively low through 2002. The abundance indices, however, fluctuated
widely from 1985 through 2002, particularly in the autumn, in response
to apparent variability in recruitment. The deviation between the
trend in biomass and abundance indices implies a reduction in mean weight
of this group in recent years. The early reduction in abundance is evident
in the distribution maps and there has been a shift in distribution from
the central Gulf of Maine to the inshore areas of the Gulf of Maine (Figure
C19).
Autumn and spring biomass and abundance indices for small-mesh groundfish show
a pattern similar to that of silver and red hake, because they are dominated
by those two species (Figure A8). All indices fluctuated considerably
since 1980, but indicate a general increase in both abundance and biomass
for this group through 2002, which is reflected by the increase in the
abundance of fish in the central Gulf of Maine (Figure
C20).
The spring indices of biomass and abundance for other groundfish in
the Gulf of Maine show an increase in the early part of the time series
to a high level in the mid-1970s (Figure A8). In the early 1980s,
a sharp decrease occurred in both biomass and abundance indices. The
spring biomass index has since continued to decline, while the abundance
index has remained constant. The autumn indices fluctuated without
trend for most of the time series (Figure A8) until the mid-1980s, when
a decline in biomass and an increase in abundance occurred. This
group of species is dominated by goosefish but also reflects the declines
noted earlier for wolffish and cusk beginning in the mid-1980s.
Georges Bank
Principal groundfish indices of biomass and abundance show similar
patterns in both seasons (Figure A9). This group was dominated
by cod and haddock through the survey period. Both spring and autumn
indices reveal a consistent pattern of increased abundance and biomass
during the 1970s, followed by sharp declines in both indices to historic
low levels during the mid-1980s. An increase and subsequent decline
in biomass in the autumn survey during the late 1980s reflects recruitment
of several low to moderate year classes of cod and haddock on Georges
Bank during the 1980s. Abundance and biomass indices were at or
near record-low levels in the mid-1990s, but increased slightly through
1997. Survey indices for this group increased through 2002, particularly
in the autumn survey due to the increases in haddock abundance and biomass. In
the early part of the time series, principal groundfish were found all
over Georges Bank (Figure C18). As the abundance declined in the
late 1980s and early 1990s, catches occurred mostly on the Northeast
Peak and in the Great South Channel.
The principal flounder indices for Georges Bank have fluctuated
considerably over the survey period, but revealed consistent declines
in abundance and biomass (Figure A9). This group was dominated
by yellowtail flounder and winter flounder. Much of the variability
in the abundance index was due to fluctuations in winter flounder recruitment,
but both species experienced consistent declines in both indices since
the late 1970s or early 1980s. Both indices were at or near historic
lows with respect to the autumn series through the early 1990s. The
subsequent increases reflected higher catches of yellowtail flounder
on the southeast part of Georges Bank (Figure
C7) and increases in winter
flounder abundance. The decline in abundance through 1993-1997 is evident
in the distribution maps (Figure C19) as well as the subsequent increase
through 2002.
Small-mesh groundfish indices of biomass and abundance fluctuated
considerably without any distinct trends throughout both spring and autumn
series (Figure A9). These indices reflect trends in both stocks
of silver hake and red hake throughout Georges Bank. As a result,
the aggregate indices do not depict consistent trends for either of the
stocks.
Abundance and biomass indices for other groundfish for both
seasons on Georges Bank display similar patterns (Figure
A9). This group
is dominated by goosefish in this region and the aggregate indices reflect
the recent decline in mean weight of the stock. Both surveys indicate
that biomass for this group through 2002 was at or near record-low levels.
Southern New England
The spring indices of principal groundfish off Southern New
England are highly variable, but indicate a general decline in abundance
and biomass over the time series (Figure A10). The autumn survey
also fluctuated with more consistent declines during the 1960s and 1970s
(Figure A10). However, the trend in abundance was affected by the
one large index in 1987, caused by three very large tows of small haddock. Most
of the principal groundfish are at the end of their geographic range
and, therefore, occur more sporadically in survey catches in this region
(Figure C18).
The indices for principal flounders off Southern New England
are dominated by yellowtail flounder and reflect the trend for this species. Abundance
and biomass declined sharply in the early 1970s, increased during the
late 1970s and early 1980s due to improved recruitment, but subsequently
declined to historic lows in the 1990s (Figure
A10). The slight
increase in 1994 (autumn) and 1995 (spring) is due to winter flounder
and windowpane flounder indices. The indices in both surveys remained
near historic lows through 2002. The distribution maps for this
group show the decline in abundance over time from the early 1960s through
1998-2002 (Figure C19).
Spring and autumn indices for small-mesh groundfish are highly
variable (Figures A10), reflecting trends in the southern stocks of red
and silver hake. The sharp but consistent decline in spring abundance
and biomass reflects overall trends for all three species in this group
and is reflected in the distribution maps (Figure
C20).
Biomass and abundance indices from spring surveys for other groundfish suggest
a sharp decline since the 1970s in both seasons (Figure
A10). The
large increase in both indices in 1981 is due to a large increase in
goosefish biomass and abundance. Abundance and biomass for this
group off Southern New England remained among the lowest on record through
1997, with some increase through 2002. The lack of fish in Southern
New England can be seen in the distribution maps (Figure
C21).
Massachusetts Inshore Survey
Biomass
and abundance indices of principal groundfish (cod, haddock, and white
hake), flatfish (yellowtail flounder, American plaice, witch flounder,
winter flounder, and windowpane flounder), small-mesh groundfish (silver
hake, red hake, and ocean pout), and other groundfish (wolffish and goosefish)
were derived for the entire Massachusetts inshore strata set (Figure
B6). MADMF spring biomass indices of each species group declined through
1997, and the autumn index of other groundfish declined. The MADMF
principal groundfish index reflects the MADMF cod index (Figure
B1),
because the catch is dominated by catches of cod. This is reflected
in the increase observed in the last five years in both spring and autumn. The
maps display a seasonal difference in distribution and the changes in
abundance over time (Figure D17). The principal flounder autumn
survey index declined in the early part of the time series, increased
through the early 1990s, and was stable for the rest of the time period.
The maps show a relatively stable abundance north of Cape Cod but a decline
in abundance south of Cape Cod, driven by winter flounder (Figure
D18). Small-mesh
groundfish inshore indices are influenced by all three species in the
group, show a decline in abundance in the spring, and fluctuate without
trend in the fall. The maps show no trends by season or time (Figure
D19). The other groundfish indices are almost identical to goosefish
and the maps are also similar (Figure D20).
Trend Analyses
The total number of time series was 160 (abundance and biomass indices
for 25 stocks from 2 to 4 surveys). At the 95% confidence level,
68 regressions were not significant, 81 estimates of r were significantly
negative, and 11 r estimates were significantly positive (5%,
or eight regressions should be falsely significant by chance, Table
2). Estimates
of r had common signs within stocks, except American plaice, and
values of r were generally similar within stocks.
All NEFSC indices of abundance and biomass significantly decreased
for Georges Bank cod, southern New England – Mid Atlantic yellowtail
flounder, southern New England – Mid Atlantic winter flounder,
southern windowpane, southern red hake, and cusk. Most MADMF indices
were also negative for these stocks, but some were insignificant. All
indices of goosefish biomass significantly decreased. The most
rapid decrease was exhibited by southern New England yellowtail NEFSC
abundance indices, which declined by nearly 10% per year (e-0.105 =
0.90).
Gulf of Maine cod, both haddock stocks, pollock, white hake, Georges
bank yellowtail, plaice, witch, Georges Bank winter flounder, southern
silver hake, ocean pout, and wolffish had significant decreases, but
regressions for some survey indices were insignificant. NEFSC
spring indices of American plaice abundance and biomass significantly
decreased, but the MADMF autumn biomass index significantly increased.
Regressions of all redfish and Gulf of Maine winter flounder indices
were insignificant. Significant increases were also found for northern
windowpane (three of four indices), northern silver hake (three of four
indices), and northern red hake (all four indices).
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CONCLUSIONS
These
results indicate that most northeast groundfish stocks significantly
decreased over the last four decades. Based on model assumptions,
it appears that total mortality rates had exceeded population growth
rates for these stocks.
Of the twenty-five stocks examined, only three stocks showed an increase
in abundance and biomass in the NEFSC surveys over the time-series. Two
stocks mostly fluctuated without trend. However, twenty (80%) of
the stocks declined throughout most of the time-series. This was
a cause for concern, since some of these stocks were considered to be "under-utilized" (NEFSC
1993). The status of some of these stocks has changed since 2002,
although most still remain at low abundance and biomass even after some
increases (Mayo and Terceiro 2005).
ACKNOWLEDGMENTS
The authors would like to express their appreciation to Ralph Mayo
and Arnie Howe for their insight and review of this paper as well as
Steve Murawski and Fred Serchuk for their thoughtful comments on earlier
drafts. We also would like to thank Daniel Sheehan for making production
of the many maps a little easier.
back to top
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