Northeast Fisheries Science Center Reference Document 02-01
Workshop on the
Effects of Fishing Gear
on
Marine Habitats off the Northeastern United States,
October 23-25, 2001, Boston, Massachusetts
by Northeast Region Essential Fish Habitat Steering Committee
National Marine Fish. Serv., 166 Water St., Woods Hole MA 02543
Print
publication date February 2002;
web version posted March 22,
2002
Citation: Northeast Region Essential Fish Habitat Steering Committee. 2002. Workshop on the Effects of Fishing Gear
on Marine Habitats off the Northeastern United States, October 23-25, 2001, Boston, Massachusetts. Northeast
Fish. Sci. Cent. Ref. Doc. 02-01; 86 p.
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ACKNOWLEDGMENTS
This report was produced by the Northeast Region Essential
Fish Habitat Steering Committee to detail the workshop panel discussions
and conclusions. The EFH Steering Committee consists of the following
individuals: Bob Reid, co-Chair (NMFS, Northeast Fisheries Science
Center), Lou Chiarella, co-Chair (NMFS, Northeast Regional Office),
Dianne Stephan (NMFS Northeast Regional Office), Mike Pentony (New
England Fishery Management Council), Tom Hoff (Mid-Atlantic Fishery
Management Council), and Carrie Selberg (Atlantic States Marine Fisheries
Commission). Korie Johnson (NMFS Office of Habitat Conservation)
joined the Committee for purposes of this workshop. David Stevenson,
John McCarthy and Meredith Lock, contractors for NMFS, also assisted
in the development of the workshop and report preparation.
The EFH Steering Committee would like the
thank the workshop panel (listed in Appendix
A) for their hard work and dedication to having a successful workshop.
Thanks to Kathie Ciarametaro for her assistance with workshop logistics.
Thanks to Jeff Citrin of Resolve, Inc. for providing workshop facilitation
services.
The workshop was sponsored by NOAA / National
Marine Fisheries Service, New England Fishery Management Council
and Mid-Atlantic Fishery Management Council.
The views expressed herein are those of the workshop
panel and do not necessarily reflect the views of the EFH Steering
Committee members, the agencies they represent, or the sponsors.
INTRODUCTION
The 1996 Amendment to the Magnuson-Stevens Fishery
Conservation and Management Act (MSFCMA) tasked the National Marine
Fisheries Service (NMFS) and federal fishery management councils
with identifying and describing essential fish habitat (EFH) for
all species that are managed under a federal fishery management
plan (FMP). Additionally, each FMP is required to identify and
assess the impacts of all fishing gears on EFH, and where practicable,
minimize any adverse effects caused by fishing.
Assessing gear impacts and implementing management
measures that will minimize the effects of fishing requires scientific
information documenting the following: the effects of different
fishing gears and practices used in the region; the distribution
of fishing effort; the distribution of habitats within the region;
the recovery rates of the effected habitats; and any reduction
of an essential fish habitat's capacity to support exploited marine
resources as a result of fishing. Studies have been conducted in
the Northeast region and in other geographic areas around the world
which address some of these questions, but to date there has been
little attempt to evaluate all of the available information in
order to identify adverse impacts to the specific habitat types
of the Northeast region. For the purposes of the workshop, the
Northeast region encompasses the area from Maine through North
Carolina. The uncertainty regarding the identification of adverse
impacts on the various habitat types found within the Northeast
has resulted in reluctance to implement risk-averse habitat protection
measures.
The workshop convened a panel of experts in the fields
of benthic ecology, fishery ecology, geology, fishing gear technology,
and fisheries gear operations (List of Participants in Appendix
A). The purpose of the panel was to assist the New England
Fishery Management Council (NEFMC), the Mid-Atlantic Fishery Management
Council (MAFMC) and NMFS with: 1) evaluating the existing scientific
research on the effects of fishing gear on benthic habitats; 2)
determining the degree of impact from various gear types on benthic
habitats in the Northeast; 3) specifying the type of evidence that
is available to support the conclusions made about the degree of
impact; 4) ranking the relative importance of gear impacts on various
habitat types; and 5) providing recommendations on measures to
minimize those adverse impacts. The workshop was held from October
23-25, 2001, in Boston, Massachusetts (Workshop Agenda in Appendix
B).
Although the workshop was entitled "The Effects
of Fishing Gear on Marine Habitats of The Northeastern United States," the
workshop focused on benthic habitats. The goal of the workshop
was to evaluate the impacts of fishing gear used in federally regulated
fisheries on habitats of the Northeast shelf ecosystem, and to
recommend management measures that will reduce those impacts (Appendix
C). Only impacts to habitat were considered; effects of fishing
on exploited species populations were not considered. Definitions
of terms, such as "adverse effect", that were used to
focus the discussions are provided in Appendix
D.
There will be two final products as a result of this
workshop. The first is this workshop report which summarizes panel
discussions and conclusions relating to the effects of fishing
gears on benthic habitats in the Northeast region. The second product
will be a peer reviewed document produced by NMFS staff which describes
gear types used in federal and state waters in the Northeast region,
the spatial distribution of fishing trips made by each gear type
in federal waters, oceanographic regimes and habitat types in the
region, and the results of scientific studies of the effects of
fishing gear on benthic habitats in the Northeast U.S. and elsewhere.
Preliminary Draft copies of this document (White Paper) were distributed
to panel members in advance of the meeting to assist them in achieving
workshop objectives. These documents will be available for use
by the NEFMC and MAFMC to fulfill their MSFCMA requirements to
include an assessment of fishing gear impacts on EFH in all of
their FMPs.
WORKSHOP
FORMAT
Although there are many fishing gear types utilized
in the Northeast region, the workshop focused on gear types that
are federally managed under the MSFCMA. An exception to this was
made for lobster pots due to their widespread use in both state
and federal waters. The following gear categories were evaluated:
Bottom-tending Static Fishing Gear
- Pots and Traps
- Sink Gill Nets, Bottom Long Lines
Bottom-tending Mobile Fishing Gear
- Clam Dredges (hydraulic and non-hydraulic)
- Otter Trawls
- Sea Scallop Dredges
- Beam Trawls
Pelagic Fishing Gears (Static and Mobile)
The panel was provided a set of 15 questions, in advance,
to guide the workshop discussions (Appendix E). These questions were
divided into four categories: gear descriptions, gear effects on
habitat, strength of evidence supporting the effects, and management
actions. Individual panelists led the discussion for each gear type,
guided by the questions. Some discussion leaders provided short presentations
on their assigned gears which were then followed by group discussions.
During the first two evenings, the discussion leaders held individual
sessions with selected experts and workshop staff to further evaluate
the available information and to prioritize the effects of each gear
type in different habitats. On the third and final day the panel
reviewed the results of these sessions.
A gear impact matrix was completed for each gear type
which summarized the degree of impact for three substrate types,
mud, sand, and gravel (Appendix D for
definitions). The panel evaluated the types of impact caused by the
gear for each substrate type, the degree of each impact, the duration
of the impact, and the type of evidence available to support these
conclusions. Four types of impacts were considered for each gear
type and habitat: 1) removal of physical features; 2) impacts to
biological structure; 3) impacts to physical structure and; 4) changes
to benthic prey (Appendix D for definitions).
After the matrices for each gear type were completed, the panel ranked
the relative significance of each gear and impact type for all three
substrate types. Once the types of impacts and habitats of greatest
concern were identified, the panel recommended management actions
that could be considered by the Councils to reduce the adverse effects
of fishing gear on benthic habitats in the Northeast region.
This report clearly identifies when panel consensus
was reached, and when points are attributed to individual panelists.
The workshop began with introductory remarks by representatives of
NMFS, MAFMC and NEFMC. The following sections summarize the introductions,
discussions, conclusions and recommendations of the panel.
INTRODUCTORY
PRESENTATIONS
NMFS Welcoming Address
Peter D. Colosi, Jr., Assistant Regional Administrator for Habitat Conservation
I am excited to welcome you to this workshop on the effects of fishing gear
on fish habitat with such a panel of knowledgeable scientists, gear technologists,
and fishermen.
As most of you are aware, with the 1996 Amendment to
the Magnuson-Stevens Fishery Conservation and Management Act, the
National Marine Fisheries Service and fishery management councils
have had the task of identifying and describing essential fish habitat
for all federally managed species. Additionally, we have had to identify
and assess the relative impacts of all fishing gears on essential
fish habitat for all of our fishery management plans, and where practicable,
minimize any adverse effects from fishing.
Assessing gear impacts and implementing management
measures to minimize impacts has been a very daunting task when faced
with limited scientific information related to gear impacts on specific
habitats, recovery rates, and the applicability of research conducted
in other locations to the Northeast. Additionally, we are currently
unable to quantify the intensity of gear interaction on specific
habitat types in the Northeast. This has lead to much uncertainty
regarding the identification of adverse impacts to the various habitat
types found within the Northeast as well as apprehension to implement
risk-averse habitat protection measures.
This panel has been convened to assist in interpreting
the existing scientific research, determining the applicability of
existing studies to the Northeast and evaluating the strength of
that evidence. Your deliberations over the next three days, will
provide valuable information to the New England and Mid-Atlantic
Fishery Management Councils for use in fulfilling the habitat requirements
of the Magnuson-Stevens Act.
I would also like to take this time to thank the Northeast
Region EFH Steering Committee, which is comprised of staff from the
National Marine Fisheries Service's Regional Office and Northeast
Fisheries Science Center, the Mid-Atlantic and New England Fishery
Management Councils and the Atlantic States Marine Fisheries Commission,
for their hard work in organizing this workshop.
Good Luck over the next several days and I look forward
to your results.
Mid-Atlantic Fishery Management Council Welcoming Address
Gary Caputi, Vice-Chairman, Ecosystem Planning Committee
On behalf of the Mid-Atlantic Fishery Management Council,
its members and staff, I'd like to welcome this distinguished group
of scientists, fishery managers and fishermen to this important workshop.
It is our hope that the documents and the recommendations for future
research produced by this gathering of specialists will help us move
forward with the responsibilities placed on our shoulders by the
Sustainable Fisheries Act.
With the passage of the Act in 1996, Congress and the
Administration charged the eight regional management councils with
identifying essential fish habitat and addressing threats to the
health and viability of that habitat. One perceived threat was specifically
identified in the language of the Act and was, therefore, required
to receive a heightened level of investigation and action in FMP
amendments. That is the impact of fishing gear on EFH or its subset,
habitat areas of particular concern (HAPCs).
In trying to meet this mandate, the Mid-Atlantic Council
has run into a problem caused by the lack of targeted scientific
data addressing specific gear types used in the wide ranging fisheries
we are responsible for managing. This poses a dilemma for managers
because we have found ourselves unable to identify whether specific
gears pose a threat or have no impact on the wide range of marine
habitats exposed to their use. The problem is a double-edged sword.
Our inability to justify positions on gear impacts has generated
disapprovals of portions of recent plan amendments in which we identified
no discernable impacts as well as those in which we identified possible
impacts. Without adequate scientific documentation, the decisions
we make are unsupported and, therefore, cannot be approved by the
Agency and the Secretary. That is why this workshop was developed
and why we have asked for this distinguished panel to convene. We
desperately need scientific documentation to support the management
objectives we assume under the Sustainable Fisheries Act so we can
we do our jobs better.
In the past, a lot of scientific investigation was
performed and scholarly papers were published on a wide variety of
subjects. Many did little to provide fishery managers with the bedrock
work they need to make better management decisions. This is not to
say that such work was not important, or that it did not serve a
purpose in furthering our understanding of the marine environment
and its workings. But when it comes to the work the Councils are
charged with performing, scientific research and documentation is
required that specifically addresses our needs. It is in the management
process that the scientific rubber meets the road and that is why
the steering committee has worked so diligently to make it clear
what we as managers need from you as scientists to make our efforts
to rebuild and maintain sustainable fisheries and protect the marine
environment more successful.
In the past two years, the Mid-Atlantic Council has
seen the "Gear Impacts" sections of four major FMPs disapproved.
They include Summer Flounder, Scup and Black Sea Bass; Surfclams
and Ocean Quahogs; Squid, Mackerel and Butterfish and the Bluefish
FMP. The amount of work involved in writing these plan amendments,
incorporating entirely new sections detailing EFH and then trying
to divine whether there are or are not threats to the identified
important habitat from fishing gear, with little or no scientific
data to fall back upon, was a frustrating exercise. One that we do
not want to see repeated. Our inability to adequately identify gear
impacts has lead to the Council and the Agency being criticized by
constituencies on all sides of this rather volatile issue.
Not only have we experienced amendment disapprovals
in major plans, but we have also been unable to justify the incorporation
of "gear restricted areas" in the Tilefish FMP. Tilefish
represent possibly the most habitat dependent of all the species
of finfish the Mid-Atlantic Council is responsible for managing.
It is a sedentary species that is believed to spend a major portion
of its life cycle in relationship to burrows in the clay bottom located
near the major canyon heads and along the edge of the continental
shelf. After a great deal of examination of the existing data, it
was "divined" that the doors of bottom tending mobile gear
presented a potential negative impact to tilefish burrows. Therefore
boundaries were developed to identify areas known to have concentrations
of burrows and the Council proposed a restriction on the use of bottom
tending mobile gear in those areas. Did the Council go too far? By
proposing this action, based on impressions gleaned from the limited
scientific study available, did the Council overstep its bounds?
Apparently so because the gear restricted area concept was found
to be unjustifiable after lengthy public hearings.
Without concise documentation, fishery managers are
damned if they do and damned if they don't act. Is it possible that
there is sufficient published literature to justify some actions
or inactions, but it simply has not been compiled into documents
that will stand up under Agency and possible judicial review? That
is for you to determine.
It is our desire to see this workshop produce a comprehensive
compendium of the work already done on identifying gear impacts to
marine habitat and also identify areas where additional work is necessary
that directly addresses the needs of managers so that we may accomplish
our mandates in a more accurate and timely manner. With that, we
wish you Godspeed and good luck in your endeavor.
New England Fishery Management Council Welcoming Address
Doug Hopkins, Chairman, Habitat Committee
Good morning and thank you for the invitation to speak
to you as you begin these important deliberations on the effects
of fishing gear on fish habitat.
My name is Doug Hopkins. I am wearing four hats, those
of New England Council member, Chair of the Council's Habitat Committee,
Environmental Defense staff member, and lawyer. So the lens through
which I view these issues may be a little different from yours.
Yes, you will identify many, many unanswered scientific
questions related to the effects of fishing gear on marine habitat
and will conclude that much additional research is needed. Nevertheless,
you can play a critical role in helping the regional councils, the
National Marine Fisheries Service and the scientific community to
avoid paralysis, and I urge you to do so.
Let's look closely at the Magnuson-Stevens Act mandate.
The law, as amended by the Sustainable Fisheries Act (SFA), allows – actually
it requires -- action by the councils and NMFS to protect habitat
from harmful fishing impacts even in the absence of thorough scientific
understanding.
Yours is not a forensic undertaking whose aim is to
present evidence for a jury to conclude beyond a reasonable doubt
what gear should be convicted of assault and battery on Essential
Fish Habitat (EFH). Congress has already reached the conclusion that
many of today's fishing gears and practices adversely affect EFH.
It is now the managers' job to implement all practicable
measures to minimize harm by fishing gear to EFH. This is what the
SFA requires. So what do we, as managers, need from you, the scientific
experts, so that we can do our jobs effectively? We need a diverse
menu of measures that singly or together will reduce the adverse
effects of fishing on habitat. We also need good explanations that
let us, fishermen and the general public understand how these measures
will provide benefits to fish habitat. In addition, and very importantly,
we need as much help as possible prioritizing these proposed measures
by characterizing the relative expected benefits of each.
Finally, and crucially, since the Magnuson-Stevens
Act requires that any fishery management plan must "minimize
to the extent practicable adverse effects on . . . [essential fish]
habitat caused by fishing," the regional councils and NMFS need
your help to systematically evaluate the practicability of each of
the measures you propose. To do this you may have to include in your
deliberations fishery economists and other experts who are not present
today for this workshop.
Addressing a few other points, first I believe the
New England Council would welcome suggestions for creating incentives
for fishermen to develop and adopt new fishing practices and gear
that would reduce harmful habitat impacts, so long as they would
in fact benefit habitat. In other words we seek your help identifying
ways to harness the enormous, proven ability of fishermen to solve
problems and increase their efficiency through innovations in gear
and fishing methods.
Next, I wish to highlight an example of a proposed
measure that needs additional scientific input to adequately evaluate
its potential. The New England Scallop Oversight Committee and the
full Council are considering a measure for possible inclusion in
Amendment 10 to the Scallop FMP that would bar future scallop fishing
from the historically least productive scallop grounds. The pertinent
scientific question then is whether data exist to determine whether
the historically least productive scallop grounds can be distinguished
from the historically most productive? The initial designation of
the least productive grounds would not have to be perfect, only scientifically
supported and practicable. If subsequent surveys disclosed that a
rare but significant set of scallops had occurred in an area initially
closed as within the historically least productive grounds, a subsequent
framework adjustment to the FMP could always reopen the area.
Touching on research needs, I want to emphasize that
the regional councils and NMFS clearly need significant input from
the scientific community to identify and prioritize additional research
that would help to answer important questions related to minimizing
the adverse effects of fishing on EFH. That said, identifying research
needs should not become an excuse for management inaction. You can
help the Councils and NMFS determine how best to encourage valuable
research. For example, we need to know: How can the New England Council
and NMFS best utilize the Research Steering Committee? Should we
be considering creating Habitat Research Areas where fishing activity
would be barred except as specifically allowed for research? If so
where should these be sited and how large should they be? How important
would it be to have baseline benthic surveys done and how should
the survey areas be prioritized, recognizing that funding won't allow
them to be completed all at once?
When it comes to research, engendering accurate expectations
of the benefits of specific research projects will be critical. The
Councils, the fishing communities and the general public need accurate
information as to how long any particular research activity will
likely take to yield results relevant to management decisions. Is
it two years, five years or 20 years? Unrealistic expectations can
damage scientific credibility among non-scientists and erode public
confidence in fishery management.
In conclusion, Congress has determined that fishing
gear and practices can and must evolve to reflect the scientific
understanding we have of the high and unnecessary cost of fishing
on the marine environment. Fishing yields food for people to eat
and money and livelihoods for fishermen and their communities. You
can help the fishery managers and fishermen to figure out better
ways to provide these yields more sustainably than current fishing
practices allow. The technology and practices used to catch fish
in New England have not changed significantly for decades, while
scientific understanding of the stresses on marine ecosystems caused
by fishing has grown dramatically during this time. This imbalance
is simply wrong. Your scientific advice will be crucial to helping
managers and fishermen change fishing gear and practices to dramatically
decrease their ecological and economic costs.
Thank you, and good luck in your deliberations over
the next three days.
HABITAT CHARACTERIZATION
Dr. Page Valentine (U.S. Geological Survey) summarized
major marine habitat characteristics applicable to the Gulf of Maine,
Georges Bank, southern New England and mid-Atlantic Bight and their
variability in terms of topography, sediment texture and hardness,
substrate roughness and surface area, substrate dynamics, water column
characteristics, habitat usage, and fishing impacts (Table
1). This is information that could be considered when evaluating
the setting, function, and vulnerability of various habitats. Additional
information was presented for eleven different geographical habitat
types on Georges Bank and in the Gulf of Maine using these generalized
habitat characters (Appendix F). No detailed
information was presented for habitat types in southern New England
and the mid-Atlantic Bight.
Panel members concluded that this was very useful information
and recommended that: 1) detailed habitat types between Cape Cod
and Cape Hatteras also be described, and 2) several new characters
be added to the habitat type descriptions. It was noted that information
is available for certain habitats (e.g., soft corals) south of Cape
Hatteras. Additional habitat characters that were suggested by panel
members were the principal types of fishing activity, estimates of
the area covered by each habitat type, and depth range. Dr. Valentine
pointed out that there is some information on the areal extent of
some of the offshore habitats he described in the Gulf of Maine – Georges
Bank region, particularly for Georges Bank itself, but thorough maps
are not available.
EFFECTS OF
FISHING GEAR
CLAM DREDGES
Gear Description
Mr. Dave Wallace (Wallace and Associates) presented a thorough description
of the evolution and current use of the hydraulic clam dredge for the
surfclam and ocean quahog fisheries. A brief discussion of "dry dredges" used
in the Maine "mahogany" ocean quahog fishery was led by Mr. Wallace
with contributions from the workshop panelists. This section of the
report summarizes his presentation and the panel discussion.
Hydraulic clam dredges have been used in the surfclam fishery for
over five decades and in the ocean quahog fishery since its inception
in the early 1970s. These dredges are highly sophisticated and are
designed to: 1) be extremely efficient (80 to 95% capture rate); 2)
produce a very low bycatch of other species; and 3) retain very few
undersized clams.
The typical dredge is 12 feet wide and about 22 feet long and uses
pressurized water jets to wash clams out of the seafloor. Towing speed
at the start of the tow is 2.5 knots and declines as the dredge accumulates
clams. The dredge is retrieved once the vessel speed drops below 1.5
knots, which can be only a few minutes in very dense beds. However,
a typical tow lasts about 15 minutes. The water jets penetrate the
sediment in front of the dredge to a depth of about 8 - 10 inches,
depending on the type of sediment and the water pressure. The water
pressure that is required to fluidize the sediment varies from 50 pounds
per square inch (psi) in coarse sand to 110 psi in finer sediments.
The objective is to use as little water as possible since too much
pressure will blow sediment into the clams and reduce product quality.
The "knife" (or "cutting bar") on the leading bottom edge of the dredge
opening is 5.5 inches deep for surfclams and 3.5 inches for ocean quahogs.
The knife "picks up" clams that have been separated from the sediment
and guides them into the body of the dredge ("the cage"). If the knife
size is not appropriate, clams can be cut and broken, resulting in
significant mortality of clams left on the bottom. The downward pressure
created by the runners on the dredge is about 1 psi.
It was pointed out by a panel member that the high water pressure
associated with the hydraulic dredge can cause damage to the flora
and fauna associated with bottom habitats. However, water pressure
greater than that required for harvesting will reduce the quality of
the clams by loading them with sand and increase the rate of clam breakage.
Therefore, water pressure is usually self regulated.
There are currently two types of hydraulic dredges used in the fishery,
stern rig dredges and side rig dredges. The chain bag on a side rig
dredge drags behind the dredge and helps smooth out the trench created
by the dredge. The chain bag results in significantly more damage to
small clams and other bycatch than occurs with the stern rig dredge.
With the stern rig dredge, which is basically a giant sieve, small
clams and bycatch fall through the bottom of the cage into the trench
and damage or injury is minimal. Improvements in gear efficiency have
reduced bottom time and helped to limit the harvest of surfclams to
a relatively small area in the mid-Atlantic Bight.
Prior to 1990, the resource was managed by controlling the number
of hours a vessel could fish. Consequently, towing speeds were maximized
to catch as many clams as possible regardless of the damage done to
the clams or the habitat. Cutting and breakage of discarded clams were
estimated to be as high as 90% in some locations and under some conditions
decomposition of dead clams caused reduced oxygen concentrations in
sediments to the point that clams were killed. Incidental mortality
is currently estimated to be well under 10% because quota management
has removed the need for vessels to catch as many clams as possible
as quickly as possible.
Concurrent with the change in harvesting practices that occurred after
1990, there has also been a significant reduction in fishing effort
and a shift to stern rig dredges. About 60 side-rig vessels pulling
80 dredges were taken out of the fishery after 1990. The number of
surfclam vessels decreased from 128 in 1990 to 31 in 2000, while the
number of vessels that landed ocean quahogs (excluding the Maine fishery)
dropped from 56 in 1990 to 29 in 2000. Currently there are only 4 side
rig vessels pulling five dredges left in the fleet.
Surfclams live mostly in sand which is disturbed and re-suspended
by storms and, in some locations, by strong bottom currents. Ocean
quahogs live at greater depths, mostly in finer sand and silt/clay
substrates which are less affected by natural physical disturbances.
Surfclams and ocean quahogs are not found in commercial quantities
in gravel or mud habitats or in depths greater than 300 feet.
Hydraulic clam dredges can be operated in areas of large grain sand,
fine sand, sand and small grain gravel, sand and small amounts of mud,
and sand and very small amounts of clay. Most tows are made in large
grain sand. Dredges are not fished in clay, mud, pebbles, rocks, coral,
large gravel greater than one half inch, or seagrass beds. Boat captains
will not dredge in areas with very soft or hard substrate where they
run the risk of losing or damaging the gear. The fishery is also limited
to sandy sediment because the processors do not want mud blown into
the clam bodies by the dredge.
The spatial scale of fishing effort varies depending on which species
is the target: surfclams are harvested primarily in a small area off
the New Jersey coast whereas ocean quahogs are harvested over a larger
area that includes offshore waters. Areas with denser concentrations
of clams would presumably be dredged more intensively, i.e., a higher
percentage of the bottom would be affected. Because surfclams are concentrated
in a very defined area off the New Jersey coast where the bottom is
so homogeneous, a high proportion of the bottom over this large contiguous
area is affected by dredging. Surfclams grow much more rapidly than
ocean quahogs and surfclam beds are dredged every few years. Areas
dredged for ocean quahogs are left untouched for many years. Ocean
quahogs are much more likely to be dredged from a number of more or
less discrete patches that are surrounded by undisturbed areas. It
was noted, as a general rule, that once 50% of the harvestable clams
are removed from an area, the catch rates drop to a point where it
is no longer economically feasible for fishing to continue there.
In federal waters, the amount of bottom area directly impacted by
the hydraulic clam dredge fleet in 2000 was about 110 square miles
(Table 2). An additional 15 square miles were dredged
in State waters of New Jersey, New York, and Massachusetts. The predominant
substrate on the southern New England/Mid-Atlantic Bight shelf is sand.
Thus, during any given year, this fishery is conducted in a very small
proportion of a habitat type that characterizes most of the 40,000
square miles of continental shelf between the Virginia/North Carolina
border and Nantucket Island (69° W longitude). The Georges Bank region
has been closed to clam harvesting since 1990 because of the potential
of paralytic shellfish poisoning.
The dry dredge used in the Maine fishery is a cage with
wide skis and a series of teeth about 6 inches long in the front. These
dredges are used on smaller boats (about 30 to 40 feet long) and are
pulled through the seabed using the boat's engine. The cutter bar is
limited to a width of 36 inches by State law. This fishery takes place
in small areas of sand and sandy mud found among bedrock outcroppings
in depths of 30 to > 250 ft in state and federal coastal waters
north of 43° 20' N latitude. The dredges scoop up clams and sediment,
and the vessel's propeller wash is used to clean out the sand and mud.
Effects
and Evidence
Dr. James Weinberg (Northeast Fisheries Science Center - NEFSC) led
the discussion of the direct physical and biological effects of hydraulic
clam dredging, and Dr. Roger Mann (Virginia Institute of Marine Science
- VIMS) led the discussion on the available evidence. Most of the evidence
for dredging impacts that was considered by the panel was from the
Northeast U.S., but there are studies from other areas that show the
same effects. It was noted that early studies done in the Northeast
region were conducted during development of the fishery, when clam
dredging was more damaging to the habitat than it is now.
According to these studies, the direct physical effects of hydraulic
clam dredging are basically two-fold. First, a trench about 8 inches
deep is left behind the dredge and windrows of sediment and organisms
are formed on either side of the trench. The second direct physical
effect is the resuspension of sediment. If a dredge goes through silt
or loose sediment, it produces a sediment cloud. In the panel's judgement,
fine sediment may take as long as 24 hours to resettle and would end
up outside the trench, while heavier particles would settle much more
rapidly, primarily back into the trench. The evidence for physical
effects (trench, windrows, and sediment re-suspension) is strong because
these effects are so obvious.
Physical impacts to bottom habitat last longer (months) in low energy
environments than in high energy environments (hours). In sand, the
sides of the trench start to erode as soon as it is cut; this happens
more rapidly when bottom currents are strong. The rate at which it
fills in depends on the grain size of the sediment, water depth, and
the strength and frequency of storms and bottom currents. It was noted
that there are permanent, longshelf, sand ridges with low elevation
off the New Jersey coast, but there is no evidence to indicate that
clam dredges remove them, even though they may be towed through them.
The direct biological effects of hydraulic dredges vary, depending
on whether organisms are hard-bodied like clams or soft-bodied like
amphipods or polychaetes. What happens when a clam dredge goes through
an area is not fully known and more study is needed. It was noted that
structure-forming epifauna such as anemones and sponges would clearly
be removed. Emergent epifauna growing on shell beds in the mid-Atlantic
Bight is known to provide cover for juvenile fish species like black
sea bass. Removal of these organisms, or their burial by re-suspended
sediments, could therefore cause the loss of habitat for some species
of juvenile fish.
It is not clear what happens to soft-bodied organisms that are moved
by the dredge or pass through the trench and are deposited back on
the seafloor. Often, after an area is dredged, scavengers move in rapidly
and eat broken clams and soft-bodied organisms that are removed from
the substrate. However, the panel considered that evidence for effects
on infaunal prey organisms was weak because there aren't many studies
that link changes in benthic community structure in dredged areas to
the food supply for fish, and those that do exist do not show definitive
results. The panel concluded that infaunal communities would be likely
to recover more quickly than emergent epifauna, and therefore removal
of structure-forming organisms was judged to be more of a concern.
However, one panelist noted that the potential loss of secondary production
of benthic invertebrates which are prey for bottom-feeding fish is
the effect that is least understood, and that any reduction in prey
abundance - if it occurs - would not necessarily be limited to the
dredge tracks themselves, but would affect the entire dredged area.
Moreover, the effects of fluidizing the sediment on benthic infauna
are unknown and may be important.
The panel noted that there may be cumulative physical and biological
effects in areas that are dredged several times annually. As previously
stated, surfclams grow much more rapidly than ocean quahogs and surfclam
beds are dredged every few years, whereas areas dredged for ocean quahogs
are left untouched for many years. It was also noted that benthic organisms
that occupy muddy bottom in deep water are less adapted to physical
disturbance and therefore would presumably take longer to recover from
dredging than organisms in sandy bottom areas in shallower water.
Conclusion
The panel concluded that the habitat effects of hydraulic dredging
were limited to sandy substrates, since the gear is not used in gravel
and mud habitats (Table 3). Two effects -changes
in physical and biological structure - were determined to occur at
high levels. The evidence cited for these two effects was a combination
of peer-reviewed scientific literature, gray literature, and professional
judgement. There are no effects of hydraulic dredges on major physical
features in sandy habitat because, in the panel's view, there are no
such features on sandy bottom. Panel members evaluated changes to benthic
prey as unknown.
The temporal scale of the effects varies depending on the background
energy of the environment. Recovery of physical structure can range
from days in high energy environments to months in low energy environments,
whereas biological structure can take months to years to recover from
dredging, depending on what species are affected.
The panel agreed that hydraulic dredges have important habitat effects,
but even in a worse case scenario, where there were known to be severe
biological impacts, only a small area is affected and therefore this
gear type is less important than other gear types like bottom trawls
and scallop dredges which affect much larger areas. It was also pointed
out, however, that even though the effects of dredging (at least for
surfclams) are limited to a relatively small area, localized effects
of dredging on EFH could be very significant if the dredged area is
a productive habitat for one or more managed fish resource. The same
would be true if dredging in a particular area coincided with a strong
settlement of larval fish. A major question for this gear is "what
are its long-term biological impacts" i.e., how, and to what
extent, are benthic communities altered in heavily dredged areas, particularly
the prey organisms, and how long does it take for them to recover once
dredging ceases?
Management
Dr. William DuPaul (VIMS) led the discussion on the types of management
actions that could be taken to minimize adverse impacts of hydraulic
dredging to benthic habitat.
The effectiveness of the Individual Transferable Quota (ITQ) management
program since 1990 and the opinion that the two resources are underfished,
led the panel to conclude that reductions in effort are probably not
practicable. Nor is it likely that gear substitutions or modifications
are practical since the current gear is highly efficient at harvesting
clams. Therefore spatial area management seems to be the only practicable
approach to minimizing gear impacts, if necessary.
It was emphasized that hydraulic dredges are designed to operate in
sandy substrate. This gear could be very destructive if fished in the
wrong sediment type or in structured environments like gravel beds
or tilefish pueblo villages. The panel emphasized the gear should not
be used in sediment types where it would cause more damage. Areas of
known structure-forming biota should be mapped and set aside as a priority.
It was emphasized that since we really do not know what the effect
of this gear is to soft-bodied benthic organisms, a possible precautionary
measure would be to restrict the fishery to areas of high clam productivity.
Seasonal closures were mentioned if times and areas of high recruitment
could be detected.
SCALLOP
DREDGES
Gear
Description
Dr. DuPaul led the discussion on scallop dredges. The New Bedford
scallop dredge was described during a general review of scallop dredges
and their use. This dredge is the primary gear used in the Georges
Bank and mid-Atlantic sea scallop (Placopecten magellanicus)
fishery. The scallop dredge used in coastal waters of the Gulf of Maine
was also described briefly. The European scallop dredge was briefly
discussed.
The forward edge of the dredge includes the cutting bar, which rides
above the surface of the substrate, creating turbulence that stirs
up the substrate and kicks objects up from the surface of the substrate
(including scallops) into the bag. Shoes on the cutting bar are in
contact with and ride along the substrate surface. The bag is made
up of metal rings with chafing gear on the bottom and twine mesh on
the top, and drags on the substrate when fished. New Bedford dredges
are typically 14 feet wide; two of them are towed by a single vessel
at speeds of 4 to 5 knots. Dredges used along the Maine coast are smaller
(5.5 to 8.5 ft). Towing times are highly variable, depending on how
many marketable sized scallops are on the bottom and the location.
Scallops are shucked at sea, but small amounts (< 50 baskets) are
returned to shore whole for specialty markets.
In the Northeast region, scallop dredges are used in high and low
energy sand environments, and high energy gravel environments. Although
gravel exists in low energy environments of deepwater banks and ridges
in the Gulf of Maine, the fishery is not prosecuted there.
Effects
and Evidence
Dr. Valentine led the discussion on the effects of scallop dredging
and Dr. Weinberg led the discussion on the available evidence. The
panel noted that much of the scientific literature is based on the
European dredge, which differs in structure and use from the New Bedford
dredge. The leading edge of the European dredge contains teeth which
dig into the substrate. This type of gear is used by smaller vessels
that are not able to tow a non-toothed dredge fast enough (4-5 knots
is necessary) to fish effectively. The panel noted that because of
these differences, research using the European dredge was not completely
relevant to North American scallop fisheries or the habitats in which
they are found, and should only be applied in a limited fashion.
An analysis of vessel monitoring system (VMS) data for vessels in
the scallop fishery provided to panel members at this workshop revealed
that the scallop fishery is highly concentrated. Total fishing activity
(dredges and trawls) in year 2000 was dispersed throughout 12,800 one
square nautical mile sub-areas, but 81% of the total catch was harvested
in only 2,946 of these sub-areas. A full description if this information
that includes plots of fishing activity in 1998 and 1999 is in Appendix
G. One panelist noted that based on his analysis of logbook data
from the mid 1980s to the mid 1990s, the distribution of fishing effort
for scallop dredges in the Northeast U.S. was patchy, with areas that
were fished intensively and other areas that were fished very lightly,
and generally did not overlap with areas that were fished heavily with
bottom trawls.
The findings of the studies summarized in the white paper which took
place in the Northeast region were discussed and considered to be applicable
to other areas of similar habitat type within the region. These findings
included:
- disruption of amphipod tube mats and decline in dominant megafaunal
species in gravelly sand in the Gulf of Maine from fishing (Langton
and Robinson 1990);
- increased epifauna (hydroids, bryozoans, sponges, serpulid worms
and sea cucumbers) on a cobble/shell bottom in an area on the Maine
coast closed to dredging and trawling in 1983 (Auster et al. 1996);
- disturbance of storm-created coarse sand ripples (10-20 cm high)
by scallop dredges on Stellwagen Bank, in the southwestern Gulf of
Maine (Auster et al. 1996);
- increased abundance of emergent sponges inside a sandy area closed
to dredging and trawling for 4.5 years (Almeida et al. 2000);
- redistributed gravel, pebbles, and boulders, flattened sand and
mud bedforms, and resuspended fine sediments caused by mussel and
scallop dredging in lower Narragansett Bay, Rhode Island (DeAlteris
et al. 1999);
- reduced epifaunal community, smoother bottom, and disturbed and
overturned boulders in gravel areas on Georges Bank affected by dredges
and trawls compared to unfished areas (Valentine and Lough 1991);
- reduced densities, biomass, and species diversity of megabenthic
organisms in disturbed gravel habitat on Georges Bank (Collie et
al. 1997);
- higher percent cover of emergent colonial epifauna in undisturbed
gravel habitat sites on Georges Bank (Collie et al. 2000).
A number of international studies were also discussed. Although the
gear differed in some of these studies as described above, findings
in these studies were considered to be relevant. The findings were
as follows:
- long-term shifts in benthic community composition in the Wadden
and Irish Seas following the introduction of scallop dredging (Reise
and Schubert 1987, Hill et al. 1999);
- increased abundance of some epifaunal species (sea urchins and
some crustaceans) in gravel areas closed to dredging in the Irish
Sea (Bradshaw et al. 2000);
- mortality of large epifauna and sand lance (Ammodytes)
in the path of the trawl in high energy sand in Scotland, with no
significant effects on abundance of mollusc or crustacean infauna
(Eleftheriou and Robertson 1992);
- loss of emergent tubes and sediment ripples and decreased density
of common macrofauna from dredging in sub-tidal sand flats in New
Zealand, with complete faunal recovery within a few months (Thrush
et al. 1995);
- reduced abundance of 6 of the 10 most common benthic infaunal species
from dredging, with recovery within 6 months for most, but greater
than 14 months for a few, in mud and sand habitat in Australia (Currie
and Parry 1996).
The panelists agreed that effects and their significance vary by habitat
type, and that research results could not be applied widely across
habitat type. The panelists also agreed that the first pass of a dredge
over an undisturbed area is expected to have more significant effects
than subsequent passes and that the return of cut shell-stock to the
environment could enhance sea floor structure and provide substrate
for settling scallop larvae. There was some discussion about the discarding
of viscera from shucked scallops and its value to EFH, but no consensus
was reached.
Several studies conducted on Georges Bank were discussed in detail.
Valentine and Lough (1991) compared trawled and dredged gravel areas
with undisturbed gravel areas and noted that the epifaunal community
was more diverse with abundant attached organisms at the undisturbed
sites. Subsequent research by Collie et al. (2000) in gravel pavement
habitat showed that Filograna implexa, a colonial,
rock-encrusting polychaete, and bushy colonial epifauna such as bryozoans
and hydroids, were more abundant in the undisturbed areas. The study
by Almeida et al. (2000) showed an increased abundance of emergent
sponges (Suberites ficus and Polymastia sp.) on sandy
bottom at stations inside Groundfish Closed Area II four and a half
years after it was closed, compared to stations just outside the area
that have remained open to bottom fishing.
The panel clarified that the results of the studies done on gravel
bottom on Georges Bank could be applied to dredged areas in the Gulf
of Maine where the same taxa are present in hard bottom habitats, but
not to sandy scallop fishing grounds in southern New England and the
mid-Atlantic Bight where different emergent epifaunal species are present
and where there are fewer epifaunal organisms growing on the bottom.
Panel members agreed that structure-forming biota that are present
in sandy habitats are just as vulnerable to scallop dredging as in
gravel habitats, but that the biological impacts of dredging on emergent
epifauna are less significant in high energy sand environments because
the organisms are better adapted to sediment disturbances caused by
storms and strong bottom currents and therefore recover more quickly
from dredging. It was noted that hard bottom benthic habitats in the
Gulf of Maine and in deeper water on Georges Bank are more vulnerable
to bottom mobile gear than sand bottom habitats south of Cape Cod because
they support more diverse and prolific epifaunal communities and because
recovery times are slower. It was also noted that long-term effects
are more significant than short-term effects and are harder to differentiate
from effects caused by environmental changes.
There was some discussion about the indirect biogeochemical effects
of sediment resuspension caused by dredging and trawling. It was noted
that the re-suspension of fine sediments (clay, silt and fine-grained
sand) could have important effects on habitat quality by releasing
nutrients, metals and contaminants that are "trapped" in anaerobic
bottom sediments. These effects would be negligible in shallow water,
coarse sand habitats. The release of nutrients could be beneficial,
but the release of metals and other contaminants could have adverse
effects on pelagic and benthic habitats. Most of the research that
has been done on this subject is in inshore coastal and estuarine waters,
not in deeper, offshore waters.
There was also some discussion about the effects of scallop dredging
on the functional value of benthic habitats for exploited marine resource
populations. Two habitat functions mentioned were: 1) cover from predators
provided for juvenile fish and prey species by emergent epifauna; and
2) the bio-energetic benefits of sand ripples and waves for bottom
fish (e.g., flounders) that seek refuge from bottom currents. The panel
noted that some studies have been conducted in these two subject areas
and others are in progress.
Conclusion
The panel determined that the effects of scallop dredging were of
greatest concern in the following three habitat types: high and low
energy sand and high energy gravel. Scallop fishing does not generally
occur in deep water, low energy gravel habitats. The basis for all
the panel's conclusions regarding the degree of impact and recovery
time estimates were a combination of peer reviewed literature, gray
literature, and the panelists' professional judgement.
Low energy sand habitat occurs in deeper water, where the bottom is
unaffected by tidal currents and where the only natural disturbance
is caused by occasional storm currents. In this habitat type, the primary
physical bottom features are shallow depressions created by scallops
and other benthic organisms. Reduction of biological structure and
changes in physical structure were both considered to occur at a high
level as a result of scallop dredging (Table 4).
Recovery of physical structure was expected to vary from days to months
depending on how long it takes different species of animals to create
new depressions in the seafloor. The degree of impact to biological
structure in low energy sand habitats was judged to be high because
emergent epifauna is more abundant in this more stable environment.
Recovery from reduction in structural biota was expected to take from
months to years.
In high energy sand habitats, effects on biological structure were
considered to be low, since organisms in this environment would be
adapted to a high degree of natural disturbance. Changes to physical
structure such as smoothing out of sand ripples, sand waves, and
sand ridges were rated as high. The range of recovery times for physical
structure in high energy sand habitat was based on the rapid recovery
time for sand ripples that are produced by bottom currents (days)
and a longer time (months) for storm-created sand waves and ridges.
Similar to low energy sand, recovery time for biological structure
was expected to range from months to years. The range in recovery
time was based on how long it would take for amphipod tubes to re-form
compared to the growth rates of sponges and other longer-lived species.
The panel did not have enough information to evaluate the effects
of scallop dredging on benthic prey in sandy bottom and therefore
concluded that the degree of this effect was unknown in both low
and high energy habitats.
In high energy gravel habitat, the panel concluded that the degree
to which biological structure was reduced by scallop dredging was
high, as were changes in physical structure, and changes in benthic
prey. Dredging disturbs gravel and pebbles, breaches gravel "pavement," and
redistributes cobbles and small boulders. Recovery of physical structure
in this habitat type was estimated to take anywhere from months to
a year. Once gravel pavement is breached, it re-forms fairly quickly
as the underlying exposed sand is removed by bottom currents leaving
gravel behind as the predominant substrate. Attached epifauna known
to be removed by scallop dredges in high energy gravel habitats include
sponges, bryozoans, hydrozoans, and colonial polychaetes. Recovery
times for biological structure were estimated as years (but fewer
than ten years).
Since many of the structure-forming organisms that are removed from
high energy gravel habitat by scallop dredges are either preyed upon
by bottom-feeding fish or provide cover for invertebrates and small
fish that are consumed by bottom-feeding fish, habitat impacts caused
by changes in prey species composition and abundance were rated as
high in this habitat type, with recovery times of months to several
years, depending on which taxa are affected. Panel members noted
that it was difficult to evaluate impacts to benthic prey in the
absence of information linking known alterations in the species composition
and abundance of benthic organisms to changes in the food supply
for fish.
The panel acknowledged that impacts of scallop dredging to sand
and gravel habitats represent two extremes in a continuum of effects
(gravel being more vulnerable) and that what happens to mixed sediment
habitat types that fall in between these two extremes is harder to
evaluate. It was also pointed out that the more important question
may not be what happens in the dredge path itself and how quickly
the seafloor and the benthic community in the dredge path recovers,
but instead what is the net impact of dredging on the affected environment
and its value to marine resources?
Management
Dr. Michael Fogarty (NEFSC) led the discussion on the management
of scallop dredge impacts. Three main approaches to minimizing habitat
impacts were discussed: effort reduction, gear modification, and
area management. Panelists noted that maintaining a high biomass
of scallops would reduce harvesting time and therefore reduce the
amount of bottom time devoted to dredging. Panelists also noted,
however, that the high initial impact of the gear on habitat (from
the first tow) could confound attempts to minimize impacts by reducing
effort.
Suggestions for gear modifications included innovations to "float" the
ring bag so it does not drag along the bottom. Use of a "hard dredge" which
only has two skids in contact with the bottom was also discussed;
however, panelists did not agree that this would be feasible since
rigid frame dredges are reportedly difficult to use and cause a higher
non-harvest mortality of scallops. Other gear modifications discussed
included development of a foil that uses a vacuum to harvest scallops.
Many panelists spoke favorably about the use of area based management.
Based on the distribution of scallop dredge fishing trips (Appendix
G), the panel noted that there are many locations where scallop
dredging does not occur. The panel discussed focusing fishing effort
in productive areas and areas without sensitive habitats. Since scallop
recruitment is episodic, some panelists felt that it was important
that all areas be available for fishing. In a rotational area management
system, the panel discussed keeping sensitive areas closed for a
longer period of time. Panelists also noted that a comprehensive
approach to area management that included consideration of the habitat
impacts of gears used in other fisheries (e.g., bottom trawls) should
be considered.
OTTER
TRAWLS
Gear
Description
Mr. Frank Mirarchi (Boat Kathleen A. Mirarchi, Inc.) and Mr. James
Lovgren (F/V Sea Dragon) identified the types of otter trawl gear
used in the northeast. They stressed the diversity of otter trawl
types used in this region, explaining that the diversity of gear
types was a result of the diversity of fisheries prosecuted and bottom
types in the region. The specific gear design used is often a result
of the target species (whether they are found on or off the bottom)
and the composition of the bottom (smooth versus rough and soft versus
hard). The presenters described the various components of otter trawls,
including the sweeps, the net body, bycatch reduction devices, bridles
or ground cables, and the doors. The sweeps can be chain-wrapped
wire, rubber cookies, rockhoppers, rollers, street-sweepers, or tickler
chains. The net body depends upon the head rope height, the amount
of overhang, and the mesh sizes of the various net panels. Bycatch
reduction devices include the Nordmore grate and mesh panels. Types
of bridles include chain, bare wire, covered wire, or seine rope.
Trawl doors can be polyvalent, flat, or vee type.
Small mesh nets are used to target whiting and squid, and these
configurations usually employ a light chain sweep. Flatfish are primarily
targeted with a mid-range mesh flat net that has more ground rigging
and is designed to get the fish up off the bottom. A high rise or
fly net is also used with larger mesh. There are three components
of the otter trawl that come in contact with the bottom: the doors;
the ground rigging behind the doors; and the sweep.
The panel members discussed these descriptions, noting that otter
trawls are actually very complex systems designed to target specific
types of fish rather than simple sieves used to collect everything
in their path. Fish herding is an important aspect of trawl design
and depends upon the hydrodynamic forces of the doors and the sediment
clouds generated by the ground rigging and sweep. Panel members reported
that roller gear is obsolete in the Northeast, having been replaced
by rockhopper gear. Rockhopper gear is no longer used only on hard
bottom habitats, but is actually quite versatile for use on a variety
of habitat types.
The panel considered the weight in water of the different otter
trawl configurations, relative to their weight on land. Contrary
to some assumptions, rockhopper gear is not the heaviest type of
otter trawl in use in this region as it loses 80% of its weight in
water (i.e., a rockhopper rig that weighs 1000 pounds on land may
only weigh 200 pounds in water). Streetsweeper gear is much heavier
due to the use of steel cores in the brush components. Cookie gear
can be heavier as it retains 80-85% of its weight in water. Plastic-based
gear has the smallest weight in water to weight on land ratio, at
approximately 5%. The panel agreed that the weight of the gear in
water is a very important consideration in understanding the relative
effects of different otter trawl configurations.
Effects
and Evidence
The discussion leaders for the effects of otter trawling were Dr.
Robert Van Dolah (South Carolina Department of Natural Resources)
and Dr. Ellen Kenchington (Department of Fisheries and Oceans, Canada).
At the outset of the discussion, the panel agreed to two general
points: first, otter trawls are one of the most studied fishing gear
types; and second, otter trawls are one of the most widely used fishing
gears. The effects of otter trawls are believed to vary by the specific
configuration used, by the intensity of the trawling activity, and
by the type of habitat in which the gear is used. Some of the panel
members were of the opinion that benthic habitats are dynamic systems,
and the changes that result from otter trawling may not necessarily
be detrimental.
The panel members discussed a variety of direct effects of the gear
operating on the bottom. These effects included: 1) the scraping
or plowing of the doors on the bottom, sometimes creating furrows
along their path; 2) sediment resuspension resulting from the turbulence
caused by the doors and the ground gear on the bottom; 3) the removal
or damage to non-target species such as benthic or demersal predators;
and 4) the removal or damage to structure-forming biota. The relative
significance and/or duration of these effects often depends upon
whether the gear is used on low versus high energy environments (these
environments could also be thought of as stable versus unstable).
It was mentioned during discussion that with the exception of the
doors, the trawl gear has to be relatively light on the bottom to
maintain its shape and effectiveness. If it rides too heavily on
the bottom the gear would collapse in on itself.
Some panel members stated that even relatively light trawl gear
will still have an impact on structure forming taxa. Discussion included
the opinion that static weight of the gear alone is not the only
factor to consider, but that the horizontal and vertical forces on
the gear (i.e., the speed of the vessel) are also important considerations.
It was agreed that more research is needed to better understand the
relationships of gear weight and the forces on the bottom and the
differences between gear types.
The panel members also discussed some potential indirect effects
of the gear operating on the bottom. The indirect effects included:
1) altered trophic function of benthic communities, primarily caused
by a reduction or change in large biota, a reduction or change in
predators, or a reduction or change in epiphytes; and 2) altered
demersal communities, primarily caused by a loss of structure-forming
biota and an alteration of physical features.
The most significant potential effects of otter trawls identified
by the panel included long-term changes in bottom structure and long-term
changes in benthic trophic function or ecosystem function. The panel
suggested that these changes may result either from a reduction of
organisms or the replacement of organisms. The potential replacement
of some organisms with other organisms is significant because this
may prevent the ecosystem from being able to return to its original
state, even in the complete absence of fishing activity.
The panel discussed a proposed model for determining the degree
of effect on various habitats. The model ranked habitat types along
a continuum from mud/sand with no major epifauna or structure-forming
biota in a high energy environment to gravel/hard bottom with abundant
epifauna and/or structure-forming biota, and suggested that the degree
and duration of the effects on these habitat types ranged from lowest
for the mud/sand with no major epifauna or structure-forming biota
in a high energy environment to highest for the gravel/hard bottom
with abundant epifauna and/or structure-forming biota. This model
utilized a variation of the major categories of effects previously
described: 1) removal of physical features, 2) reduction of structural
biota (impacts to biological structure), and 3) reduction of habitat
complexity and sea floor structure (impacts to physical structure).
Generally, there was a low level of concern for the effects of trawling
in mud and sand habitats without major epifauna or structure-forming
biota, but a high level of concern for gravel and hard bottom habitats
with epifauna and/or structure-forming biota. There was some discussion
among the panel members as to whether mud deserved its own category,
based on the deep-water basins in the Gulf of Maine that contain
long-lived epifauna, but there was no consensus on this issue. The
degree and duration of a fourth category of effect, changes in benthic
prey, was suggested as being case specific. This conceptual model
is discussed in more detail in a subsequent section.
The panel discussion identified several indirect effects of otter
trawls on different habitat types, including the attraction/movement
of scavengers into the area behind the trawl and changes in diatoms
and other primary producers. It was suggested that although scavengers
are attracted to areas recently trawled, they do not move in from
great distances. Rather, the scavengers that are already in the general
vicinity do well, but there are not significant increases in the
numbers of these scavengers. It was also suggested that there may
be important cascading effects of the changes in diatoms and other
primary producers.
The panel discussed the changes in habitat complexity resulting
from the tracks made by the doors in further detail. The door tracks
themselves create an increase in complexity at the scale for small
organisms, but there is a net loss in complexity due to the reduction
of biogenic structure. The panel also discussed the duration of effects
and agreed to define "long-term" as whenever the recovery period
is longer than the natural period of disturbance. The panel agreed
that the duration of effect would be greater in habitats toward the
gravel/hard bottom with epifauna and/or structure-forming biota end
of the continuum identified above.
Following the discussion on the types and relative importance of
the different effects of otter trawling on benthic habitats, the
panel discussed the strength of the scientific evidence for these
effects. This discussion was led by Dr. James Lindholm (Stellwagen
Bank National Marine Sanctuary). The panel agreed that there is a
great deal of literature to apply to otter trawl fishing activities
in the northeast. Most of the available information can be applied
to otter trawls in general and deals with chronic effects rather
than acute effects. The most difficult issue remains establishing
the link between the alteration of the habitat and the effects on
biological communities.
It was suggested that ultimately, to make real progress on these
issues, we need to be able to look at the differential effects of
fishing gear on different types of habitats, and be able to do this
by the type of otter trawl rather than only considering otter trawls
in general. The current situation is limited to the generalized effects
of otter trawls, without the ability to tease out the good and bad
elements of these fishing activities. This situation also creates
a problem for conservation engineering because there are no specific
objectives or problems to solve, only generalities.
In spite of this problem, there was agreement that the general principles
and results of the worldwide body of literature on the effects of
otter trawling on benthic habitats were applicable to the northeast,
even though the gear used might be slightly different. Of all the
gears the panel has been charged with considering, otter trawls represent
the type where the results of studies from other areas are the most
applicable. The panel generally agreed that there was strong evidence
in the scientific literature for each of the four primary types of
effects as identified earlier.
Conclusion
The panel concluded that the greatest impacts from otter trawls
occur in low and high energy gravel habitats and in hard clay outcroppings
(Table 5). In gravel, the greatest effects were
determined to be on major physical features, and physical and biological
structure of the habitat. The panel found it was unable to reach
consensus on the degree of impact for sand and low energy mud habitats,
but a majority of panel members agreed upon the final conclusions
in Table 5.
In gravel and other hard bottom habitats, the degree of impact of
otter trawls on major physical features, physical structure, and
biological structure were all considered to be high in both low and
high energy environments. Major physical features in this habitat
type are boulder mounds, which can be knocked down by trawls. Once
this happens, the mounds can never be re-formed, and the resulting
changes are permanent. Trawls also cause alterations to physical
structure by redistributing cobbles and boulders and breaching gravel
pavement. Impacts to biological structure in gravel were of greater
concern to the panel than impacts to biological structure in other
habitats because structural biota is more abundant on gravel bottom.
Effects to physical and biological structure of these habitats were
judged to last from months to years. The basis for all the panel's
conclusions were professional judgement, peer-reviewed literature,
and gray literature. Changes to benthic prey caused by trawling were
considered to be unknown. In mud habitats, the panel distinguished
between hard clay outcroppings that occur in deep water on the outer
continental shelf and soft mud (silt and clay) sediments found in
deep water basins in the Gulf of Maine and many shallower locations
on the shelf. Bottom trawling takes place in both of these habitat
types.
Clay outcroppings are found on the slopes of submarine canyons that
intersect the shelf on the southern edge of Georges Bank and the
New York Bight. These outcroppings provide important habitat for
tilefish (Lopholatilus chamaelonticeps) and other benthic
organisms which burrow into the clay. Based on the panel's professional
judgement, removal of this material by trawls was considered to be
a permanent change to a major physical feature, and was rated as
a high degree of impact. The panel determined that trawls could also
cause a high degree of impact to the physical structure of hard clay
habitat that could last from months to years. This determination
was based on peer reviewed and gray literature, and the panel's professional
judgement. Due to a lack of information, the panel was not able to
rate impacts to biological structure or benthic prey in this habitat
type.
The panel did not reach consensus on the degree to which otter trawls
affect physical and biological structure in soft mud habitats. However,
most panelists agreed that impacts to biological structure (including
worm tubes and burrows) and physical structure were moderate. Panelists
agreed that these impacts would be expected to last from months to
years. Peer reviewed and gray literature and professional judgement
were relied on to make determinations about impacts to physical structure,
while professional judgement was the only basis for determination
of impacts to biological structure. A lack of information prevented
the panel from drawing conclusions about impacts to benthic prey.
Panelists determined that removal of major physical features was
not a concern in this relatively featureless habitat.
Determining the impacts from trawling on sand habitat was particularly
difficult for the panel. There was no consensus on the degree of
impact to biological or physical structure, or to benthic prey, in
high and low energy environments. However, with one exception, the
panelists agreed that these impacts were moderate. Trawl induced
changes to physical structure in high energy sand were rated as low.
Recovery times for biological structure and prey were considered
to range from months to years, and for physical structure from days
to months. The basis for all determinations was peer reviewed and
gray literature, and professional judgement. The panel determined
that removal of major physical features was not an impact that applied
in what is a relatively featureless environment.
There was a general consensus that the acute impacts of bottom trawls
(i.e., impacts caused by a single tow) on physical and biological
structure are less severe than for a scallop dredge, but the chronic
impacts resulting from repeated tows are more severe for trawls because
a greater bottom area is affected by trawling than is affected by
scallop dredging. Additionally, otter trawls are towed repeatedly
in the same locations, much more so than scallop dredges and clam
dredges. One panel member pointed out that the only part of a trawl
that disturbs the bottom in the same manner as a scallop dredge is
the door - the rest of the trawl behaves very differently. Another
panel member reiterated that there are a large variety of trawls
in use in the Northeast U.S. Some (squid nets, high rises) are very
light trawls that barely contact the bottom at all, whereas others
(flatfish nets) "hit hard" which makes it difficult to generalize
the impacts associated with this gear. It is important to recognize
that the greatest challenge the panel faced in drawing their conclusions
is the fact that there is such a wide variety of otter trawl gear
in use over a very wide range of habitat types and known impacts
from trawl gear is aggregated and not typically attributed to a specific
gear configuration.
Management
Dr. Joseph DeAlteris, (University of Rhode Island) was the discussion
leader for the management section and offered a framework of management
approaches that could be considered for reducing the impacts associated
with otter trawls on benthic habitats. The approaches included
effort reductions, area restrictions, and gear improvements. He
acknowledged that fishing effort by bottom-tending mobile gear
has been reduced approximately 50% in the Northeast over the last
ten years. He also acknowledged that the existing year-round closed
areas (Georges Bank Closed Areas I and II, the Nantucket Lightship
Closed Area, and the Western Gulf of Maine Closed Area) have been
effective at reducing fishing-related impacts within the areas.
He suggested that there are ways to make fishing gear more "habitat-friendly" by
lowering the associated turbulence and making the gear lighter
on the bottom, but stressed that these efforts would require cooperative
work with the fishing industry and specific goals and objectives.
Overall, the panel agreed with the discussion leader on these points
as general principles.
The panel discussed these management approaches. Panel members
suggested that reductions in effort do not necessarily translate
into similar reductions in impacts, while area closures guarantee
protection to the areas closed that effort reductions cannot. Panel
members also suggested that what is really needed is an adjustment
to fishing capacity, and that over-capacity in the fleet is forcing
people to fish in ways and in areas that they otherwise would not.
Excess fishing power results in people fishing very inefficiently
at lower catch-per-unit-effort (CPUE) than would otherwise occur
and this results in increased fishing time. The panel members suggested
that conservation engineering is a key management factor to develop
fishing gears that have less impact on benthic habitats. It was
also suggested that the concept of closed areas should be revisited
to target specific habitats and bycatch concerns, and that the
areas closed could be more discrete.
The panel also identified the link between effort reduction and
specific closed areas as an important consideration in evaluating
the effectiveness of management measures. By itself, effort reduction
may not accomplish the objective of reducing impacts to habitat.
Ideally, the three components identified by the discussion leader
(effort reduction, closed areas, gear improvement) would be used
together to manage fishing activities. The panel was cautioned
that the concept of effort reduction is not necessarily as simple
as it sounds. Managers must be able to deal with latent effort
and changes in fishing behavior, the differences between nominal
effort and effective effort, and issues related to effort displacement.
For example, in response to a reduction in the allowable fishing
effort, vessels may move inshore, but this could increase the impacts
to inshore habitats.
The panel agreed that another management challenge will be the
need to consider how to protect habitat from adverse impacts from
otter trawls and other fishing gears in the context of a rebuilt
fishery when fishing effort would likely increase.
POTS
AND TRAPS
Gear
Description
Pots and traps were described by Mr. Arnold Carr (Massachusetts
Division of Marine Fisheries). Mr. Carr's descriptions focused
on lobster, seabass, scup, red crab and hagfish pots. Even though
the intent of the workshop was to focus only on gears used in federally-managed
fisheries, lobster pots were included because they are by far the
most commonly used gear in this category and because they could
potentially affect habitats that support federally-managed resources.
Lobster Pots: Mr. Carr pointed out that these are fished
as either 1) a single pot per buoy (although two pots per buoy
are used in Cape Cod Bay, and three pots per buoy in Maine waters),
or 2) a "trawl" or line with up to 100 pots. It was also pointed
out that habitat impacts are probably due mostly to the pots and
the mainline between pots, not the buoy line. Other important features
of lobster pots and their use were the following:
- About 95% of lobster pots are made of plastic-coated wire.
- Floating mainlines may be up to 25 feet off bottom.
- Sinklines are sometimes used where marine mammals are a concern
- neutrally buoyant lines may soon be required in Cape Cod Bay.
- Soak time depends on season and location - usually 1-3 days
in inshore waters in warm weather, to weeks in colder waters.
- Offshore pots are larger (more than 4 ft long) and heavier
(~ 100 lb.), with an average of ~ 40 pots/trawl and 44 trawls/vessel;
they usually have a one-week soak and a floating mainline.
- There has been a three-fold increase in lobster pots fished
since the 1960s, with more than four million pots now in use.
Other Pots: Seabass/scup and red crab pots are similar
in design to lobster pots. Seabass/scup pots are usually fished
singly or in trawls of up to 25 pots, in shallower waters than
the offshore lobster pots and red crab pots. Pots may be set and
retrieved 3-4 times/day when fishing for scup. The red crab fishery
uses 400-600 pots/vessel, hauled on a daily basis, and operates
on the continental slope and canyons. Hagfish pots (40 plastic
gallon barrels) are fished in deep waters, on mud bottoms.
Effects
and Evidence
Mr. Carr led the discussion on the habitat effects that can be
attributed to pots. Most of the discussion focused on lobster pots.
The primary direct impacts of any kind of pot are the scouring
of the bottom and injury or death to benthic organisms that occur
directly under the pot or in its path when it is retrieved. The
total impact is thus the aggregate effect of the pot's "footprint," the
area through which it is dragged when it is hauled (which may be
2-3 times larger than its footprint), any damage caused by the
mainline in a trawl of pots, the number of pots that are in use
in any period of time, and the number of times each pot is hauled.
Although panel members agreed that the habitat impacts caused by
individual lobster pots were minimal, they believed that the cumulative
effects of so many pots could be significant, especially in sensitive
habitat areas of high structural complexity. Panel members also
mentioned that lobster pots normally remain on the same place on
the bottom for days at a time and that they are set repeatedly
in certain heavily-fished areas; both of these factors further
magnify their site-specific impacts on benthic habitats.
Lobsters concentrate in coastal, hard substrate areas, offshore
canyons, and in mud substrate with a high clay content where they
produce burrows. The types of habitat that the panel considered
most vulnerable to alteration by pot fishing were complex hard
bottom habitats with abundant structural biota. The panel did not
consider high-energy sand habitats to be vulnerable, and pointed
out that lobster pots are usually not fished there except during
times of the year when lobsters move across open areas of bottom.
Other observations made by panel members included the following:
- Sinking mainlines can turn over rocks and shear off epifauna
when pots are hauled.
- Lobstermen tend to avoid using sinklines in rocks.
- Attached epifauna in low energy mud and sand habitats are susceptible
to damage from sinklines, which are used in relatively flat,
featureless bottoms.
- Baits used in pots enrich benthic ecosystems and may increase
the abundance of infaunal benthic organisms in heavily-fished
locations.
- Pots may also act as reef habitat, though this effect is reduced
by their frequent retrieval.
- At certain times of year, pots indirectly provide some habitat
protection by making areas inaccessible to mobile gear.
Dr. Doug Rader (Environmental Defense) led the discussion of the
evidence and pointed out that there is some published evidence
from Florida and the Caribbean of damage to hard substrates, benthic
epifauna, and submerged aquatic vegetation. He also mentioned an
evaluation of the habitat impacts of fish pots in the Gulf of Mexico
as ranging from "an impact" to "a significant impact" (as opposed
to "no impact" or an "extreme impact). The panel agreed that there
is a paucity of information for the Northeast U.S., but studies
from other regions are applicable if they address impacts to analogous
species of emergent epifauna or types of biogenic structure.
Conclusion
The panel concluded (Table 6) that the degree
of impact caused by pots and traps to biological and physical structure
and to benthic prey in mud, sand and gravel habitats was low. In
both mud and sand, the duration of impacts to biological structure
could last for months to years, whereas physical structure and
benthic prey should recover in days to months. Professional judgement
was used to make the evaluations for benthic prey, while the panel
relied on grey literature for the other types of impacts. In gravel,
reduction of structural biota and changes in seafloor structure
and benthic prey could all persist for months to years. Again,
the panel relied on professional judgement to assess changes to
benthic prey, while grey literature was also considered for the
other impacts. In all three habitats, changes in benthic prey could
be negative, due to damage by the gear, and may be positive or
negative due to nutrient enrichment or food availability from bait.
Management
The strongest recommendation made by the panel to minimize adverse
effects of pots and traps was a reduction of effort, although
it was recognized that reducing the total number of pots in use
is not a complete solution since the remaining pots could be
set more often or left for longer set times. Other suggestions
made by panel members were:
- "Zoning" habitats (i.e., identifying zones within each habitat
type for various uses, including habitat protection) and protecting
sensitive areas (e.g., clay pipes).
- If pots can be made lighter without lifting off the bottom,
impacts could be reduced.
- Minimizing the amount of line on the bottom would also be
helpful.
- Fewer pots per string would reduce impacts of dragging the
gear across the bottom.
These observations focused on lobster pots, but some apply to
other types of pots as well. Pot fisheries for black sea bass
and conch in certain locations are also characterized by a high
density of pots which maximizes the likelihood of site-specific
habitat impacts.
SINK
GILL NETS AND BOTTOM LONGLINES
Gear
Description
These two gears were described by Mr. Carr. Other types of bottom
static gear (e.g., stake gill nets, handlines, electric or hydraulic
reels) were not covered because they are not used extensively
in federal waters.
Sink/Anchor Gill Nets: Individual gill nets are typically 300
feet long, and are usually fished as a series of 5-15 nets attached
end-to-end. Gill nets have three components: leadline, webline
and floatline. Fishermen are now experimenting with two leadlines.
Leadlines used in New England are ~65 lb/net; in the Middle Atlantic
leadlines may be heavier. Weblines are monofilament, with the
mesh size depending on the target species. Nets are anchored
at each end, using materials such as pieces of railroad track,
sash weights, or Danforth anchors, depending on currents. Anchors
and leadlines have the most contact with the bottom. Some nets
may be tended several times/day, e.g., when fishing for bluefish
in the Middle Atlantic; for New England groundfish, frequency
of tending ranges from daily to biweekly.
Bottom Longlines: Mr. Carr was most familiar with longlines
fished off Chatham, MA, where about six vessels use them. Up
to six individual longlines are strung together, for a total
length of about 1500 ft, and are deployed with 20-24 lb anchors.
The mainline is parachute cord or sometimes stainless steel wire.
Gangions (lines from mainline to hooks) are 15 inches long and
3-6 ft apart. The mainline, hooks, and gangions all come in contact
with the bottom. Circle hooks are potentially less damaging to
habitat features than other hook shapes. These longlines are
usually set for only a few hours at a time. Other panelists noted
that: 1) the soak time is regulated, such that the longlines
cannot remain in the water for very extended periods; 2) longlines
for tilefish in deep water may be up to 25 miles long, are stainless
steel or galvanized wire, and are deployed in a zig-zag fashion;
and 3) in the Southeast, longlines are prohibited in waters less
than 300 ft deep (except for sharks), and are also prohibited
in the wreckfish fishery (which is generally prosecuted in depths
from about 1200-2000 ft). The prohibition is due to evidence
of damage to corals, lost gear, and conflicts with other gears.
Effects
and Evidence
Discussions of effects and strength of evidence were led by
Dr. Robert Diaz (VIMS) and Dr. DeAlteris. It was noted that both
gears are dragged over the bottom when they are retrieved. In
addition, gill nets move around to some extent while they are
on the bottom and longlines can be moved back and forth across
the bottom if there is enough current or when hooked fish pull
on the mainline. Dr. Diaz noted that direct effects could include
alteration of physical structure and injury or death of emergent
epifauna, while indirect effects could include alterations of
benthic assemblages toward species that provide less cover or
prey for demersal fish. He also pointed out that the amount of
damage will depend on the frequency and duration of sets, and
the amount and type of structure present. Mr. Carr, who has done
research on lost or abandoned gill nets in New England, observed
damage to bottom habitats caused by trapped schools of dogfish
dragging the nets across the bottom.
Dr. DeAlteris noted that observations in an area off Alaska
indicated that the effects of bottom longlines could be of the
same type and magnitude as those caused by mobile gear, if longlines
are used intensively in areas with abundant biological structure.
However, these gears cause relatively little harm when used in
non-sensitive habitats that have little or no vertical physical
or biological structure. Vulnerable areas are those with 1-3
ft tall structure. Dr. DeAlteris also noted that in order to
fully evaluate the significance of the habitat impacts of these
two gear types in the Northeast region, the types of gear used
and how they are used need to be matched up with the types of
habitat where they are used. Two other factors to consider are
the amount of gear used and the total area affected.
Except for observations of "ghost" gill nets, there are no studies
of the habitat impacts of either of these gear types in the Northeast
region. However, in the opinion of Dr. DeAlteris, studies from
other areas could be applied to the Northeast, as long as the
gear was used in the same type of habitat.
Several panel members noted that tilefish are unusually important
in structuring the bottom in offshore canyon head areas. These
areas then become important habitat for lobsters, crabs and other
species, and that removal of these fish (with longlines) should
perhaps be considered a habitat effect, as it may lead to reduced
burrow-forming and maintenance. It was noted that part of the
continental shelf break habitat for golden tilefish in the Southeast
U.S. is now protected, and research is being done on the value
of this habitat.
Conclusion
The panel concluded that sink gill nets and longlines cause
some low degree impacts in mud, sand and gravel habitats (Table
7). In mud the impacts to biological structure could last
for months to years. Duration of impacts to physical structure
could be days to months on soft muds, and permanent if impacts
were on hard bottom clay structures found in deep water on the
continental slope. Impacts to physical structure in mud would
be caused by lead lines and anchors used with sink gill nets,
not by longlines. In the panel's judgement, impacts in sand would
be limited to biological structure and would last days to months.
The panel's evaluations of impacts in mud and sand habitats were
based on professional judgement alone. Impacts in gravel would
also be to biological structure, and the duration could be months
to permanent (the latter if the damage involved corals), as indicated
by peer review and gray literature, as well as professional judgement.
Management
The panel agreed that better information is needed on the
distribution of habitats that are sensitive to alteration from
sink gill nets or bottom longlines, and recommended that sensitive
habitats be protected through closures. It was also pointed
out that there are areas where emergent epifauna would naturally
grow, but has been removed by mobile bottom gear. The panel
also suggested that gill net and longline vessels should have
observers to record bycatch of benthic structural material.
BEAM
TRAWLS
Description
Dr. Chris Glass (Manomet Center for Conservation Sciences)
and Mr. Mirarchi led the panel discussion on beam trawls. The
panel was unaware of any beam trawls being used in the Northeast
U.S. at this time. A few beam trawls were used in the 1970s
to catch monkfish, but the fishery was unsuccessful. In the
mid 1990s, a number of boats off New Bedford used what were
referred to as beam trawls, but the gear more closely resembled
a scallop dredge rather than the traditional, European beam
trawls. There are a few boats that are currently coded as beam
trawls in the fishery landings database, but the panel felt
that these were most likely miscoded and were otter trawls
being deployed from the side of the vessels.
The panel also felt that it is unlikely that fishermen would
begin using beam trawls in the Northeast U.S. Beam trawls are
prevalent in the North Sea where the water is dark and murky
and the fisheries target flatfishes, which sit slightly under
the sediments. In these fisheries, the beam trawl acts to sieve
the fish up off the seafloor. The lack of conventional herding
effect and small mouth opening of the beam trawl would not
be effective for harvesting U.S. target species. Furthermore,
most vessels being used in the Northeastern U.S. do not have
the size or power required to handle a beam trawl.
Effects
and Evidence
There has been long standing concern (dating back to the 14th century)
about the adverse effects resulting from the use of beam trawls.
Therefore, there exists a large body of good information on
the effects of this gear on different habitats.
Management
No management measures are necessary at this time. This issue
should be revisited if beam trawls start being used in the
Northeast in the future.
PELAGIC
GEAR
Description
Dr. DeAlteris discussed a number of pelagic gear types used
in the Northeast, including pelagic trawls, drift gill nets,
purse seines and longlines. The discussion focused on the fact
that, if operated correctly, pelagic fishing gear should only
incidentally come into contact with the seafloor. Pelagic trawls,
for example, are not designed to touch the seafloor and would
be damaged by such contact. Furthermore, the trawl doors would
be unstable and would not fish correctly. Purse seines are
fished primarily in offshore areas to target tunas. Only a
small number of vessels (5 or 6) use purse seines to fish for
tunas in coastal waters. Drift (i.e., floating) gill nets and
longlines (which are fished in deep waters) only inadvertnetly
contact the seafloor. Paired midwater trawls have been banned
except for herring, and drift gill nets, once employed for
swordfish, are no longer in use.
Effects
and Evidence
Dr. DeAlteris and Dr. Fogarty led the discussions on effects
and evidence. It was stated that if pelagic gear were to incidentally
contact the seafloor, the trawl doors, footropes, leadlines
of stationary or floating nets, the nets themselves, or components
of longlines could drag across benthic habitats or become entangled
on benthic structures. Occasionally boats fishing with purse
seines follow fish into shallow water depths where the height
of the net (the only one the boat is equipped with) could cause
dragging along the seafloor. In the Northeast, purse seines
were permitted into Groundfish Closed Area II in 2000 and 2001
with observers. No benthic materials came up in the nets during
those observed trips. A few boats observed in 1996 captured
benthic materials in the net when it was fished in the shallow
waters of Massachusetts Bay. This contact with the bottom is
accidental and normally is avoided to prevent damage to the
nets.
The opinion of the panel was that pelagic gear has a lower
priority than gear that is intentionally dragged across the
seafloor. There would be more concern over the potential effects
of pelagic fishing gears if seafloor contact was other than
incidental, or if there was evidence that contact occurred
frequently. Therefore, the panel concluded that we need a better
understanding of how often contact occurs. For example, West
Coast fisheries that use purse seines such that they frequently
contact bottom habitats are monitored with 100% observer coverage.
The panel also discussed ecosystem implications of pelagic
gear due to removal of pelagic prey items. It was determined,
however, that this issue would be more appropriately addressed
through the population management provisions of the Magnuson-Stevens
Act, rather than the EFH provisions of the Act.
Management
No management measures are necessary at this time, however,
Councils and NMFS should consider increasing observer coverage
to track, to the extent possible, the frequency that pelagic
gear comes into contact with the seafloor.
CONCEPTUAL
HABITAT IMPACT MODEL
Dr. Fogarty and Dr. DeAlteris presented a conceptual habitat impact
model which was partially described in the previous Otter Trawl section.
Although this model has not been extensively reviewed and discussed by
the panel, the panel agreed that the model did relate habitat impacts,
structural complexity of habitats and recovery time rather well. Based
upon the panel's agreement as to the merits of this conceptual model
it is presented here in greater detail.
Habitat Classification
and Assessment
The potential impacts of fishing gear on a habitat type are a function
of the structural complexity of the habitat, the expected recovery time
following a disturbance, and characteristics of the gear itself. Habitats
characterized by high structural complexity (including emergent biological
structures (EBS) such as attached macroalgae, epibenthic organisms etc.)
are expected to exhibit higher levels of vulnerability to disturbance.
The expected recovery time for a habitat is a function of its physical
and biological characteristics and geological structure. For habitats
with high complexity attributable to biological structure, the life history
and generation times of the emergent or attached organisms will critically
determine recovery times. Disturbance to geological structures such as
cobble/boulder mounds may effectively be permanent. The expected recovery
times for certain organisms that contribute to structural complexity
of the environment (e.g. hard and soft corals) may be measured on decadal
time scales. Conversely, disturbance to sand/mud substrates without emergent
biological structure is expected principally to involve short term impacts
and rapid recovery times.
Although a number of habitat classification schemes are possible (e.g.
Auster 1998), most involve consideration of grain size characteristics
and the presence or absence of biogenic structure. For the purposes of
assessing priority for protection, we propose a simple classification
scheme with the following categories:
mud/sand without emergent biological structure
mud/sand with emergent biological structure
small gravel (< 2cm) without emergent/attached biological structure
small gravel (< 2cm) with emergent/attached biological structure
shell aggregations and/or reefs without emergent/attached biological structure
shell aggregations and/or reefs with emergent/attached biological structure
cobble/boulder without emergent/attached biological structure
cobble/boulder with emergent/attached biological structure
We expect a general relationship between the structural complexity of
these habitat types and recovery time from a disturbance. The specific
geological and biogenic structures impacted by particular fishing gears
will of course determine if recovery is possible and, if so, the expected
time scales. Highest vulnerability to fishing gear occurs in habitat
types with high structural complexity and long recovery times. Although
the specific biological and geological characteristics of particular
habitats must be assessed to determine vulnerability to fishing gear,
we propose a general conceptual model for the purpose of defining areas
of potential high vulnerability (Figure 1).
Consideration of the physical oceanographic characteristics in the habitats
will also be critical. In high energy environments, we anticipate coarser
grain size and biological communities adapted to disturbance. The expected
impact of additional anthropogenic disturbance due to fishing activities
must be assessed with respect to rates and magnitude of natural disturbance.
In low energy environments, we anticipate biological communities that
are not adapted to natural disturbance regimes and these communities
may be particularly vulnerable to fishing gear impacts.
Consideration of priorities for protection must also consider the relative
availability of particular habitat types. Rarer habitat types should
be accorded high priority for protection with the highest priority assigned
to those habitats with low availability and high expected recovery times
(Figure 2). In the Northeast region, habitat with low
structural complexity and short recovery times are relatively abundant.
Conversely, habitats with high structural complexity and long recovery
times are comparatively less abundant. These characteristics lead to
the shape of the curve depicted in Figure 2. Types
of protection can range from constraints on particular gear types in
specific habitats to the establishment of marine protected areas in which
all extractive activities are prohibited.
PRIORITIZATION OF
IMPACTS
The workshop participants were asked to participate in an exercise to
rank the relative importance of various gear impacts on habitat. The
panelists considered the three general habitat types of mud, sand and
gravel, and within those habitat types four impacts 1) Removal of major
physical features, 2) Impacts to biological structure, 3) Impacts to
physical structure, and 4) Changes in benthic prey.
All of these impacts and habitat types were tabulated on a large chart.
The panelists were allowed seven votes each. They voted by placing stickers
on the chart next to the combinations of impacts and habitats that they
felt were the most critical. They could allocate their votes as they
saw fit based on any criteria they chose. Some panelists did not specify
the type of impact and simply voted by gear type and habitat type. The
results from this exercise are found in Table 8 and Table
9.
Several conclusions can be drawn from this evaluation. First of all,
gravel habitat was clearly considered to be most at risk, followed by
sand and mud (Figure 3). Secondly, impacts to biological
structure were of greatest concern, particularly in gravel habitat, followed
by any impacts to gravel habitat (Figure 4). Impacts
to physical structure ranked third and removal of major physical features
ranked fourth. Thirdly, otter trawls and scallop dredges were of much
greater concern than clam dredges, gill nets and longlines, and pots
and traps (Figures 5). Otter trawls and scallop dredges
were judged to have the greatest impacts on gravel habitat (Figure
6). Additionally, otter trawl effects were of concern in all three
habitat types, whereas scallop dredge effects are limited to gravel and
sand, and clam dredging impacts are limited to sandy bottom. Sink gill
nets and bottom longlines were only of concern in gravel. Changes in
benthic prey received no votes at all and only one vote was cast for
pots and traps. Overall, the panelists stated that this was a valuable
exercise and that the results were consistent with their discussions
throughout the workshop.
RECOMMENDATIONS FOR
ACTION
Overall the panel stressed a theme throughout the workshop that in order
to protect habitat from gear impacts three management measures deserve
consideration: 1) effort reduction, 2) spatial closures, and 3) gear
modification. During this specific session of the workshop these themes
were raised again and the panel also made several other and more specific
suggestions related to gear impacts and habitat. The panel members were
free to suggest anything they thought appropriate but were asked to consider
both research and management recommendations. For the most part the panel
reached consensus on each of these recommendations. When they did not
reach consensus, it is noted and the reasons for differing opinions are
explained. Many of the recommendations focused in three areas, spatial
closures, increased mapping, and effort data. The discussions supporting
these three types of recommendations along with the other recommendations
offered by the panel are included below. The panel recommended:
Spatial Closures: To protect critical and/or
vulnerable habitat areas as an important tool to minimize gear impacts
on habitat. The panel indicated that some closed areas need to be closed
to all gear types in order to protect critical habitat while other areas
only need to be closed to gear types that significantly impact the bottom.
Some panel members argued that long term and even permanent closed areas
were needed for habitat protection as well as for research. Other panel
members thought that short term or more temporary closed areas, which
adapted to changing conditions in the habitat or fishery, were sufficient.
While all panel members agreed that areas should be closed to protect
critical or vulnerable habitat , some panel members emphasized the need
to protect portions of representative habitat types in the Northeast
region; such closures would include habitats that may not be as vulnerable
to alteration from fishing. All panel members agreed that the selection
of closed areas should be based on scientific information. Some panel
members felt it was important to extend the duration of the current closed
areas on Georges Bank and the western Gulf of Maine in order to continue
habitat protection which is already in place and to allow established
research programs to continue. Other panel members indicated that these
areas were chosen for fishery resource management rather than habitat
protection purposes and therefore new areas should be considered.
Mapping: The habitats in the Northeast region
should be mapped. This mapping effort should begin with the most critical
habitats but then should eventually encompass the entire region.
Effort Data: Effort data for the various fishing
fleets, especially otter trawls and clam dredges, should be gathered
and mapped as has been done in the scallop fishery. While systems such
as VMS are currently installed on some vessels for enforcement purposes,
the panel agreed that collection of real time trip data was not necessary;
instead, any mechanism to gather information that could be mapped at
a later date would be sufficient.
Effort Reduction: The panel noted that for
many overexploited species, resource management measures which require
reductions in fishing effort to maximize yield will have the added benefit
of protecting habitat.
Gear Modification: Continued gear research
and modification. Throughout the workshop, gear modification was mentioned
as a possible way to reduce the impact of certain gears on critical or
vulnerable habitats.
Enforcement: Law enforcement for current and
any future closed areas should be improved.
Reduce damage to habitat in low yield areas: Identifying
areas of low yield of bottom dwelling resources and prohibiting fishing
with bottom-tending gear in those areas. This would reduce habitat damage
while at the same time minimizing socioeconomic impacts to fishing communities.
Some panel members disagreed with this recommendation, indicating that
if an area is not productive for fishery resources than it is most likely
not productive habitat.
Research: Funding should be provided to support
additional research that would address information deficiencies identified
in this workshop. Some panel members recommended that greater use be
made of observers to collect detailed information on bycatch and the
distribution of fishing effort. Additionally it was noted that deep water
corals, the continental shelf break, and the heads of submarine canyons
are also very important habitats that require more research to understand
their importance and provide appropriate protection measures.
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