COASTAL FISHERY RESEARCH PRIORITIES
Gulf of Maine Aquarium
January 10, 2001
Our thanks to the many people who have made
this project happen. It would not
have been undertaken without the commitment and vision of Linda Mercer,
Director of the Bureau of Resource Management at the Maine Department of
Marine Resources (DMR). Her
participation at every step of the way is an integral part of the final
product. Particular thanks go for her careful editing of the document.
Sue Inches, Director of Industry Development at DMR saw the opportunity
to get funding and has provided support throughout.
Paul Anderson, Director of the Maine Sea Grant Marine Extension Program
(MSGMEP), provided funding and his planning skills, took excellent notes, and
generously contributed his staff. The
staff of DMR and MSGMEP helped in the planning and in making both the
substance and the details of the meetings work.
Finally, without the fishermen and scientists who attended the
meetings, this project would not have gone forward nor produced worthwhile
Gulf of Maine Aquarium
DEPARTMENT OF MARINE RESOURCES
COASTAL FISHERY RESEARCH
SHRIMP (Pandalus borealis)
Northern shrimp, (Pandalus
borealis) had a landed value of $3.16 million in Maine in 1999. The
fishery is conducted by two gear types: drag and trap, for which a total
of 555 licenses were issued in 2000. Shrimp is pursued by groundfish
draggers of all sizes as well as by lobster boats that rig over in the winter to
drag or trap them. The shrimp license is a new license, created in 1999.
Prior to that, shrimp fishermen fished under a Maine commercial fishing license.
There is no limited entry in this fishery, despite considerable discussion of
the issue during the last several years.
The fishery is
managed by the Maine Department of Marine Resources (DMR) which participates
with New Hampshire and Massachusetts in the Atlantic Marine Fisheries
Commission's (ASMFC) Northern Shrimp Section's shrimp plan. Under that
plan, fishermen are required to use a 1 3/4" mesh size in the body of the
net and cod end and to use a Nordmore grate to reduce bycatch of finfish.
The plan establishes a season of 183 days maximum between December 1 and May 31.
The season length is set each year based on summer shrimp stock assessment
surveys and advice from the industry advisors.
occur in arctic and sub-arctic waters and are at the southernmost extent of
their range here in the Atlantic. Gulf of Maine shrimp populations are
cyclic, appearing to be linked to temperature cycles. The shrimp life
cycle is complex. Northern shrimp are hermaphrodites, maturing first as
males at roughly 2 1/2 years old and transforming to females at roughly 3 1/2
years. After spawning, eggs are carried on the abdomen of the females
which move into inshore waters in late fall and winter. Shrimp is an
important link in marine food chains, preying on both plankton and benthic
invertebrates and being consumed by many commercially important groundfish.
Maine dominates the
shrimp fishery -- it pioneered the fishery in the 1940s and 1950s and today
catches over 75% of the annual landings. Shrimp populations have
declined in recent years and ASMFC is starting to draft an amendment to its plan
that will include additional management measures. That plan is scheduled
for adoption in June 2001.
II. The DMR
Research Priorities Project
shrimp research priorities were developed as part of a larger research
agenda-setting effort conducted by the Maine Department of Marine Resources
(DMR) for five of Maine's major commercial species: clams, lobsters,
scallops, sea urchins, and shrimp.
research priorities was identified during the late 1990’s as a key strategy to
accomplish several of DMR's agency goals as well as the King Administration's
1996 Jobs from the Sea Initiative. The ultimate purpose of this DMR
research priority project is to ensure that fishery management decisions are
based upon the best scientific and technical information so that Maine's marine
resources are sustainable and productive. The articulation of an agenda
will also accomplish several other goals. First, by establishing and
communicating a shared vision of comprehensive research needs, it will stimulate
a market for research that serves the state's needs. Second, DMR will be
able to direct internal funding decisions appropriately and identify and involve
potential research partners from the broader marine science community, including
the fisheries and aquaculture industries. Third, the agenda will hopefully
enable the entire marine science community to develop quick responses to outside
funding opportunities on topics that serve the state's needs.
The project was
conducted under contract by the Gulf of Maine Aquarium (GMA). It was
funded by a planning grant from the Economic Development Administration, the
DMR, and the University of Maine Sea Grant Program. The GMA consultants,
DMR, and University of Maine Marine Extension Team staffed the project.
For each fishery, at
least one all-day meeting was held. The meetings were designed to be
non-regulatory, neutral, and inclusive following a format developed by GMA in
previous efforts for other species. The meetings brought together fishermen,
academic scientists, government scientists, and fishery managers as equals.
They created an open environment for curiosity and questioning. Seven
meetings were held on five fisheries to achieve broad input along the coast.
Four topics were
chosen for each species and scientists were invited to make short presentations
on each of the topics. In addition each of the presenters were asked to
write a short analysis on some aspect of the topic or his/her research questions
for the final report.
ran from 9 a.m. to 5 p.m. with breaks and lunch provided. Each day was
divided into four sessions, each on a specific topic pertinent to the species.
The format was the same for each of the four sessions. First, the group
spent ten or fifteen minutes brainstorming the questions they had about the
resource. Then the invited presenter gave a short presentation on the
selected topic and his or her major research questions about the species.
After that, the group discussed the topic and the presentation, generating a
list of questions that were summarized by one of the facilitators for later
ranking. At the end of the day, one half hour was spent in an informal
ranking process where everyone was given 10 sticky notes to stick by the topics
of their choice. The day wrapped up with an oral evaluation and discussion
of follow-up and ways to improve the process.
Publicity for the
meetings was customized for each fishery. Methods included direct mail to
license holders, personal contact with association leaders, and posters
distributed to sites in each town. All of the meetings were covered in
press releases to local and statewide papers.
Research Priority Meeting
The shrimp meeting was held at
the DMR Laboratory in West Boothbay Harbor, ME, May 12, 2000 from 9 a.m. to 5
p.m. Topics and presenters included:
1. Stock Assessment
Mike Armstrong, Ph.D., MA Division of Marine Fisheries
David Townsend, Ph.D., University of Maine
3. Life History
Dan Schick, DMR
4. Economics and Gear Amy
Schick, Atlantic States Marine Fisheries Commission
attended the shrimp meeting. Industry members included shrimp draggers and
trappers, processors, buyers, many of who have been involved in shrimp
management as advisors for years. Scientific attendees came from
National Marine Fisheries Service in Woods Hole, University of Maine, as well as
state agencies in New England including DMR scientific staff involved with
Results of the
meetings are presented in two different formats:
Priorities voted by the group (Section VI) which are presented with context; and
A detailed, categorized listing of questions, observations, and opinions
articulated during the discussion (Section VII).
The dual format is
necessary in order to capture the richness of the meeting. The priorities
organize thought and focus effort. The details are essential because the
local observations and questions provide the raw material of good scientific
hypothesis. Although the shrimp meeting was divided into four segments:
Stock Assessment, Oceanography, Life History, and Economic and Gear Issues, the
report is not structured around those categories except where it makes sense.
Many topics, such as growth and reproduction, and oceanography were raised in
several of the segments. Therefore we have given precedence to the
priorities articulated at the meeting rather than those used to organize the
meeting. Furthermore, we have not attempted to categorize the research
questions by scientific discipline. Under a given priority one might find
questions for oceanographers, basic biologists, and economists or
anthropologists. The solutions to these problems require collaboration
between disciplines and between science and industry. The first step is to
articulate the questions in such a way that a researchers and industry are
exposed to the question's rich context.
In every workshop
there were questions and suggestions about management process and communication
between fishermen, scientists, and managers. We have included these
observations and suggestions in the report. We have not included specific
suggestions for management measures because those fall outside the scope of this
Priority Research Questions
Research Context and
Group Research Priorities
The discussion at
the shrimp meeting focused on four subject areas: basic biological and
oceanographic questions, habitat, and access issues. Although quite
detailed discussion took place about specific improvements to the shrimp
assessment models, no one at the meeting -- the scientific community, managers,
or fishermen -- gave any priority to development of new assessment models.
Instead, the focus was on understanding the underlying mechanisms of
oceanography and shrimp biology and behavior that affect the shrimp population.
Habitat and access issues rose to the top of the priority setting exercise
despite the fact that there was no presentation or extensive discussion on
either topic. Prioritization of the many oceanographic and biological
questions was done by the group using the filter of the immediacy of its use in
management, either in restructuring survey or model design, or in explaining
bottlenecks in the shrimp lifecycle that can provide a direction to management.
Questions in areas of socio-economic, habitat, and gear-related research were
not articulated as fully as were questions in the other areas because of the
interests and expertise of those who attended this particular meeting.
Habitat and gear research both were rated as high priority, despite the lack of
development of the ideas in discussion.
1: Shrimp Life History and Behavior
Much is still
unknown about the basic biology and behavior of Northern shrimp. (D.
Schick, Appendix.) Little is known about timing, release, and subsequent
behavior of shrimp larvae. Likewise it is not known even how long a shrimp
is a juvenile -- one year or two -- a problem that is compounded by the
inability to age a crustacean. Little is known about the inshore/offshore
migration of juveniles, or the age at sexual maturity as a male. Migration
is poorly understood for all life stages, of particular importance both for the
design of the summer shrimp survey and for understanding the relationship
between population size and availability to the gear. Finally, there is
evidence that as the population is stressed, some males are making the
transition to females in the same season that they normally would be males,
something that has serious implications for management.
What are the key factors in shrimp larval survival? Can environmental
conditions at the time of larval release be used as a predictor of shrimp year
Describe shrimp juvenile life history, especially its duration, to provide
better assumptions for stock assessment models.
What factors regulate timing of juvenile shrimp migrations, sexual
transformation (male to female) and female inshore/offshore migration?
What factors such as density dependence are operating to determine shrimp sexual
life history is a black box: Nothing is known about the juveniles.
How long are they juveniles? One year or two? Is their growth
rate fast enough so that the mature males are indeed two and a half years
old when they mate, or is it slower, so that the males are three and one
half years old at mating?”
Shrimp Priority 2: Effects of
Large-scale Oceanographic Events on Shrimp
Shrimp is a
cold-water species that is at the southern extent of its Atlantic range in the
Gulf of Maine. It has long been known that shrimp are highly sensitive to
temperature. In fact, for many years, it was assumed that environmental
factors far outweighed fishing pressure in determining year-class strength and
that the predominant role of management was to optimize the value of the year
classes. Modern oceanographic tools are providing us with a much more
sophisticated understanding of the Gulf's oceanography and it is now possible to
ask more detailed questions about the relationship between temperature and
The flow of warm, salty slope water through the
Northeast Channel into the deep basins in the gulf and the flow of relatively
fresh, cold Scotian Shelf water into the gulf at the surface (>50 m) set up a
pattern that can roughly be described as cold on the bottom and warm on top in
the western Gulf of Maine and warm on the bottom and cold on top in the eastern
half of the Gulf from Penobscot Bay east into the Bay of Fundy. These
flows, in turn, are affected by the North Atlantic Oscillation, which is a
periodic (about every 10-years) flip-flop of atmospheric pressure between
Iceland and the Azores. When the difference is positive, it increases the
flow of cold Labrador Slope water down the coast of North America, which appears
to limit the amount of warm slope water that enters the deep Gulf of Maine.
The information gathered from large-scale oceanographic research provides a
foundation from which it is possible to ask basic questions about how
temperature, salinity, and nutrient levels operate in the shrimp life history.
Refine our understanding of the effects of large-scale oceanographic events such
as the North Atlantic Oscillation, El Nino, and global warming on the Gulf of
Evaluate the physical and biological effects of oceanographic events relative to
the shrimp population.
Shrimp Priority 3: Habitat and Gear
ranked very high despite minimal discussion at the meeting. Questions
included the impact of trawl gear on the bottom communities, environmental
issues, and the issue of refuges. Given the polarization that exists over
trawling, attention to the objectivity and credibility of trawl impact research
is most important. Despite little discussion of these issues, bycatch and
gear design issues in the fishery include the potential need for gear
modification when and if groundfish (including redfish) populations rebound.
Conduct objective, collaborative research on the effect of shrimp trawl gear on
benthic habitats, substrate, and animals.
Do shrimp have any refuges from gear in the Gulf of Maine and if so, what is
their significance to the shrimp population?
Continue conservation engineering for shrimp traps and trawls as needed to meet
changing fishery conditions and new knowledge.
can the bycatch of non-target species be minimized?”
can the catch of males, small females and egg bearing females be
can the bycatch of non-target species be characterized outside of the
small mesh exemption area?”
4: Access Issues
Access issues are a
high priority because shrimp is one of the few fisheries left in Maine that does
not have some form of controlled or limited entry. The fishery is
seasonal, and is virtually entirely a secondary fishery. For this reason,
access issues raise serious discussion of what multi-species management is and
the importance of flexibility to fishermen. The fishery is important to
Maine groundfish boats for which it provides a profitable alternative fishery
when they are limited by their federal allotments of groundfish days-at-sea.
The fishery has also traditionally provided an important winter fishery for
inshore fishermen and lobstermen throughout the state. Last year, a bill
to control entry was defeated in the Maine Legislature.
Develop and evaluate options for multi-species management that considers the
interests of all Maine shrimpers and gear types.
Develop a framework to aid evaluation of the impact of limited entry proposals
on the Maine fishing industry when and if such proposals come forward.
Document the economic and social consequences of loss of flexibility to Maine's
commercial fishermen as they have lost access to other fisheries under limited
that incorporate environmental variables and changes in life history
parameters and recruitment would be especially useful.”
P. Armstrong, Ph.D.
5: Communication and Collaboration in Shrimp Assessment
participation were a strident theme at the shrimp meeting, particularly between
industry and management. The gradual shift in shrimp management from the
state and Northern Shrimp Section to Washington as ASFMC staffers work on a
major revision of the shrimp plan has caused dismay and disillusionment among
those fishermen who have traditionally participated in shrimp management.
Fishermen stated they felt relegated to merely commenting, and being represented
by one advisor on the plan development team, rather than having responsibility
for the fishery.
The industry wanted
more fundamental inclusion in research priority setting, collaboration on shrimp
survey design and execution, and wanted better explanation of the assessment.
Fishermen want to have a formal role in deciding uses of the Shrimp Fund funded
by the Maine shrimp license fees.
Provide a catalyst for shrimp industry collaboration in setting research
priorities, making decisions on research funding, survey design and execution,
and the development of a larval survey.
Shrimp Observations and Questions from Discussion
models the effect of environmental variables such as temperature, oceanographic
phenomena, and predators on shrimp population size.
Evaluate past DeLury
model predictions against subsequent catches.
Could a West Coast
model that accounts for variable natural mortality be applied to this fishery?
Given that shrimp
apparently shows a parent/progeny relationship in addition to correlation
between environmental effects and stock size, would development of multiple
indices provide better management advice from assessment?
estimate of natural mortality from fishing mortality.
with predictive information by understanding the relationship of population size
to availability to the fishery.
the apparent direct parent/progeny relationship in the population.
reference points that are flexible, able to be changed based on updated
Develop methods for
determining shrimp age from length and developmental stage information to
improve the information in age-structured models.
Need a better
explanation of the assessment: What information goes in and what comes
out. What information is not used?
Evaluate impact of
the late season in 1999-2000. Did it allow better reproduction? Can
we know that sooner than summer 2001?
Set up an industry
committee to advise DMR on using Shrimp Fund funded by shrimp license fees. Or,
let the committee be the decision-makers on use of the fund.
Industry has lost
its sense of responsibility for shrimp management as management shifts to
Washington, DC. They now feel like token advisors, not managers.
Study the history of shrimp management and document factors that contribute to
about the development of the ASMFC shrimp plan on the Web for easy access by
gear/habitat work to make it credible, objective.
What are effects of
the chlorine in sewage outflows on plankton, and thus on shrimp? Cite work done
on Maine Yankee in 1970s.
currently uses 1" bar spacing. Most other grate fisheries use
3/4". When groundfish population grows will need 3/4" bar.
How will we deal
with redfish bycatch even with grate?
Will we need to
change the mesh size if we have a large number of fish that are just at the
selection point for the mesh size?
Document effects of
fishing the grate upside down on catch of flatfish.
What is the effect
of gear on benthic habitats, substrate, and animals?
Are there areas
where shrimp gear can't get the shrimp that act as refuges? Are these
important for the population?
Has gear efficiency
evolved to eliminate refuges?
areas help the shrimp population?
What is the
efficiency of traps at different times of year?
What determines egg
drop? Why was it early in 1999-2000 season?
understanding and estimate of natural mortality.
Role of predators in
plankton/feed in shrimp populations.
What are the
triggers for larval release? Why does it occur progressively from west to
east along the coast?
What is the
distribution of larvae in the water column and along the coast?
What are the key
factors in larval survival?
conditions at time of larval release be used as predictor of year class
Mine historical data
of larvae in water column from NMFS long term planktonic sampling. Has
this data been collected at a time when it would show shrimp larvae?
Virtually nothing is
known about juvenile life history. How long do shrimp stay in the juvenile
stage: One year or two? Accepted growth curves assume males are two
and a half years old when they mate. Is this true or are they a year older
shrimp: abundance, diet, how they avoid predators. First step is
sample collection by fishermen.
What are the
juvenile shrimp migration patterns and how do they relate to the timing and
location of the summer survey?
maturation as males change with location in the Gulf of Maine? Large males
often found in Three Dory Ridge area; smaller males often found in Jeffreys
What cue triggers
transition from male to female? A hormone?
Does stock size
influence sexual differentiation?
relationship between population size and availability to the fishery.
What is the
relationship between shrimp population size and availability to the gear?
Is the population so
stressed that more males are making the transition into females in the first
season of maturity as males? To what degree?
Can and should
environmental factors (temperature, salinity?) be incorporated in summer survey
Evaluate the effect
of the late season on shrimp aggregation and migration behavior and resultant
effect of the fishery on population.
Can we develop a
larval survey that is useful as a predictor?
Can we use an
environmental parameter such as surface temperature as a reliable indicator of
Where are the
juveniles, for how long, what is their behavior?
What are the effects
on sex transformation of stock size, density, and environmental factors?
The process of
imposing limited entry will draw more people into the fishery. Stop trying
to limit entry.
Document the process
of loss of flexibility as fishermen have been locked into specific fisheries.
participation as a basis for assigning rights does not result in equitable
treatment for fishermen.
Analyze the way
limited groundfish days affect boats' behavior in shrimp fishery.
Need for ecosystem
management instead of just individual species.
Model and compare
two management scenarios: no management for shrimp and the current system.
Environmental effects may be so strong there is no effect from management.
Model effect of
shrimp movements and days fished on market price and the catchability of shrimp.
Migration and Behavior
Where are the shrimp
in the water column at each life stage/time of day and what are the significant
oceanographic factors for each life stage?
How do shrimp move
with changes in water temperature?
Is it true that
adult shrimp will move with water temperature but not travel through the
thermocline as Spencer Apollonio found?
Do larvae have
diurnal migration as adult shrimp do?
Do all or most of
the juveniles migrate to at least the 50-fathom curve by mid-summer so they are
fully available to the survey? What is their distribution over time?
What is known about
Why do shrimp
migrate in the Gulf of Maine and nowhere else in the world?
What controls the
timing and degree of approach to shore of the female inshore migration?
What controls their offshore migration? Does timing and location of
migration vary year to year?
Can shrimp maintain
their position vertically in the water column to stay in a preferred
Why are there more
shrimp inshore right now than ever before?
Don't see any
significant increase in shrimp inshore now but significant absence of shrimp on
Cashes Ledge. Why?
salinity variations probably have an effect on survey results because they
affect the movement and location of shrimp.
Many odd phenomena
in 1998 including lobsters not on traditional bottom when they shed.
Why do shrimp behave
so differently in different areas? John's Bay year ago, catch at night;
Sheepscot shrimp not on bottom until daytime.
large-scale oceanographic phenomena and are developing indices such as the
presence of copepods.
Weather reports and
water temperature are useful in fishing: Usually after the lobsters stop
(in late fall) shrimp start in about 10 days.
Atlantic Oscillation and shrimp year class strength. Work in the bottom
effects (temperature affecting embryonic development) and the plankton blooms
(availability of food.)
Effects of light on
plankton blooms/presence relative to shrimp year class success.
information and the population spatially because populations move.
between the oceanography and the life history stages (temperature, food
Use historical data
from many sources -- NMFS groundfish surveys, cloud cover, etc. in developing
relationships between oceanography and shrimp population.
Is Maine's shrimp
stock part of a larger stock we don't have much control over or is it an
larvae from eggs released in one area on shrimp in another.
Is larval supply
from local stocks?
Improve ability to
catch/classify larvae and use larval surveys to get an early indication of year
participation in larval surveys in February and March.
Expand and use
alternate equipment and surveys to supplement existing surveys.
Try parallel tows
with a shrimp boat and the tuned survey gear to check the survey gear.
Use technology such
as Simrad/Netmind/Scanmar to verify fishing parameters of survey gear.
What is the
correlation between the trawl survey data and the trap catch data? Should
there be surveys using traps?
be included in trawl survey experimental design? If so, should bottom
temperature or surface temperature be used?
NORTHERN SHRIMP RESEARCH
May 12, 2000 at DMR
Laboratory, W. Boothbay Harbor
MA. Div. of Marine Fisheries, Gloucester
P.O. Box 27, Sunset 04683
U Maine, Orono
Amy Schick Atlantic States Marine Fisheries Commission
NMFS/NEFSC, Woods Hole, MA
F/V Jeanne C
P.O. Box 109, Wiscasset 04578
DMR, Boothbay Harbor
Lincoln County News 563-3171
Bill Sherman Southport
George Richardson 6 Jewett Cove Rd., Westport 04578
James Fossett Pemaquid 677-3689
Dan Schick DMR, Boothbay Harbor
Dale Prentice P.O. Box 25, Bristol 04539 563-3576
Butch Thompson P.O. Box 176, Port Clyde 04855
102 Townsend Ave., Boothbay Harbor 04538
Spencer Fuller 72 Commercial St., Portland 772-2299
Jeffery Reid 31 Penwood Ave, Kennebunk 967-5508
Charles Saunders 4 Sunrise Lane, Cundy’s Harbor 04079
Joho Seiders 8 Sunset Coop, S. Bristol 04568
UM Darling Marine Center, Walpole 04573 563-3146 x248
UM Darling Marine Center, Walpole 04573 563-3146 x254
P.O. Box 289, New Harbor 04554
DMR, Boothbay Harbor
Sea Grant/UM Cooperative Extension
Sea Grant/UM Cooperative Extension 563-3146 x205
Sea Grant/UM Cooperative Extension
PO Box 274, Stonington 04681
Life History the Northern Shrimp in the Gulf of
Daniel Schick, Maine Department of Marine
DMR Coastal Fishery Research Priority Meetings
The distribution of
this species on a worldwide basis is pan sub-arctic. It is found in the
Pacific, Atlantic and Arctic Oceans both above and below the Arctic Circle.
The species is fished in most of its known locations. The Gulf of Maine is
the southern limit of its range in the Atlantic Ocean. Being on the edge
of its range, it is sensitive to environmental shifts in the gulf.
The distribution of
northern shrimp relative to substrate type shows it has a preference for soft,
high-organic mud. This could provide a means of concentrating the females
in the inshore mud-bottom channels during the winter migration. It also
means that this species is highly available to mobile fishing gear since the
gear favors bottom that is more easily towed.
The life history of
northern shrimp varies to some extent with location. For instance, in the
Gulf of Maine, shrimp live an estimated five years, changing sex from male to
female at age three. In Iceland, these shrimp live over nine years and
change sex at age five. However, the maximum size of shrimp in the Gulf of
Maine is larger than it is in Iceland.
In the Gulf of
Maine, female shrimp mate in deep (70-100 fathom), offshore water in the early
fall as they extrude their eggs onto their pleopods. They remain offshore
until early winter and then migrate inshore (25-50 fathom). Hatching
occurs in mid-winter and the females will remain inshore for a short period of
time, then migrate back offshore. The larvae will go through four instars
and then settle to the bottom. At some point, they will start migrating
vertically on a diurnal basis and continue this except when bearing eggs.
They will remain inshore for about a year, then migrate offshore and develop
into mature males by the time they are two and a half years old. They will
mate and then remain offshore while going through transition into females.
As females, they will mate offshore at age three and a half, extrude their eggs,
migrate inshore, remain inshore until their eggs hatch, migrate offshore and
repeat the mating, migration and hatching one more time as a five year old
shrimp. Very few females survive long beyond their second inshore
migration. Ages are assumed from length frequency distributions of the
population since age cannot be determined in crustaceans.
description of northern shrimp life history tells in general what we do know.
The following is a list of what we don’t know and a little about why it is
important to further understand these shrimp:
distribution and survival
Timing of larval release progresses from west to east along the coast. Why
does this occur and can this be used in management?
Larvae are in water for 4 weeks +/- going through their four instar stages.
We know little about their distribution, both along the coast and vertically in
the water column. Do they migrate vertically diurnally as the adults do?
What are the key factors in larval survival? Is it the simultaneous
occurrence of larvae and food in the water column? If so, how does the
differential timing of larval release along the coast affect this? Can
environmental conditions at the time of larval release be used as a predictor of
year class strength?
Black box. Nothing is known about the juveniles.
Duration: One year or two? Is their growth rate fast enough so that
the mature males are indeed two and a half years old when they mate, or is it
slower, so that the males are three and one half years old at mating?
Accepted growth curves assume the former.
Timing relative to the summer shrimp cruise: How good an estimate of
recruitment is the 1.5-year class peak? Do all or most of the juveniles
migrate to at least the 50-fathom curve by mid summer so they are fully
available to the survey? What is their distribution over time?
at sexual maturation: male
Does this change with location in the Gulf of Maine? Large males are often
found in 3 Dory Ridge area, while relatively smaller males are often found in
Late fall to spring: What drives the timing of the change?
migration inshore and back offshore
Timing of approach to shore: What drives this migration?
Degree of approach to shore: What controls the degree of approach?
That is, how close to shore do the females come and does this vary along the
coast from year to year?
Timing of leaving shore: The females leave shore one week to two weeks
after larval release. Is this timing only related to larval release?
Timing of reaggregation offshore: This seems to occur in mid-May, but does
this vary in time and space?
of first molt after egg hatch
Seems to occur as females start their offshore migration.
How long does this process take and how long is it until the new shells are
To what extent is this molt related to the assumed low survival of second year
females? Does this represent a maximum age or a maximum size?
The relation of the fecundity of individuals to density, size of population,
size of year class and temperature seems to show variability. What are the
drivers that determine fecundity? How many berried females do you need to
protect until larval hatching to replace or build the population? Does
this number vary with environmental conditions?
There is some evidence of occasional years where a portion of the males go
through transition several months early to the point where they become females
during the same spawning period as their male year classmates. What drives
this process? Should management of the resource react to these events and
if so, how?
Oceanography of the Gulf of Maine Can Vary
that might be important to shrimp and other marine resources)
Townsend, Ph.D., University of Maine
DMR Coastal Fishery Research Priority Meetings
May 12, 2000
Northern Shrimp Policy, Economics and Gear
Amy Schick, Atlantic States Marine Fisheries
DMR Coastal Fishery Research Priority Meetings
Gear - Current Uses
▫ Mesh size
▫ Nordmore grate
▫ Double Nordmore grate
▫ Cod end strengthener
▫ non-target species
▫ appropriate shrimp life stages
Characterize bycatch beyond the small mesh exemption area
How can the bycatch of non-target species be minimized?
How can the catch of males, small females and egg bearing females be minimized?
How can the bycatch of non-target species be characterized outside of the small
- Current Uses
▫ market conditions
▫ price of shrimp
▫ ex-vessel value
▫ Product flow and utilization
Costs-benefits of fishing
Incorporate economics into the stock assessment
When is harvesting most profitable?
How do market conditions influence harvest?
How does the interaction with other fisheries influence the decision to fish for
Risk analysis and uncertainty
Biological reference points
Development of bio-economic model
Interaction of the shrimp fleet with other fisheries
How can risk and uncertainty be better characterized?
▪ What influence do
environmental conditions have on northern shrimp abundance and distribution?
Stock Assessment of
Northern Shrimp in the Gulf of Maine
P. Armstrong, Ph.D., Massachusetts Division of Marine Fisheries
DMR Coastal Fishery Research Priority Meetings
The northern shrimp stock in the Gulf of Maine
has been assessed annually since 1974. In the early years, assessments
consisted of total landings estimates, indices of abundance from Northeast
Fishery Science Center (NEFSC) groundfish surveys, fishing mortality estimates
from Maine shrimp survey length frequencies, and yield per recruit modeling.
The Northern Shrimp Technical Committee developed a port sampling program in the
early 1980s to characterize catch at length and developmental stage. In
the summer of 1983 it established a research trawl survey dedicated to
monitoring relative abundance, biomass, size structure and demographics of the
shrimp stock throughout the Gulf of Maine. Subsequent stock assessments
provided more detailed description of landings, size composition of catch,
patterns in fishing effort, catch per unit effort, relative year class strength,
and survey indices of total abundance and biomass. While an improvement
over earlier efforts, these assessments remained primarily descriptive,
providing qualitative advice to the managers.
Beginning in 1997, the northern shrimp stock in
the Gulf of Maine has been evaluated more quantitatively using three analytical
models that incorporate much of the available data:
Collie-Sissenwine analysis (modified Delury) that tracks removals of shrimp
using summer survey indices of recruits and fully-recruited shrimp scaled to
total catch in numbers (from dealers’ reports and port sampling);
A surplus production analysis that models the biomass dynamics of the stock with
a longer times series of total landings and three survey indices of stock
A yield-per-recruit (YPR) model and an eggs-per-recruit (EPR) model that
simulate the life history of northern shrimp (including growth rates, transition
rates, natural mortality, and fecundity) and fishing mortality on recruited
shrimp. It uses estimates of trawl selectivity to estimate yield and egg
production at various levels of fishing mortality, providing guidance on what
levels of fishing are most productive and sustainable.
The assessment could be termed “data rich”
relative to most other assessments in the U.S. Accurate accounting of
landings through dealer reports (and verified through Vessel Trip Reports),
intensive port sampling in all three producer states for characterization of
landings, and three sources of survey indices, including a comprehensive,
dedicated summer survey, provide outstanding inputs for the models.
In addition to the quantitative modeling,
descriptive information continues to be collected that provides confirmation to
the modeling. Information from port sampling and surveys such as timing of
egg drop, size at transition, relative year class strength, proportions of
developmental stages in the catch, and location of catches all provide
additional information for assessing the condition of the stock.
The current quantitative models are excellent
tools with which to evaluate the resource, yet each has strengths and
weaknesses. For instance, the surplus production model provides a good
long term tracking of the overall population but poorly tracks recruitment in
individual years. The Collie-Sissenwine model provides good real-time
information about recruitment, mortality and stock size, but only uses one
survey index and covers a shorter time scale than the production model.
The YPR and EPR models are good for evaluating reference points but do not
provide current estimates of stock size or fishing mortality.
While the current assessment is regarded as a
reliable basis for management, there are many ways in which the assessment could
The development of other models that give historic or current estimates of stock
size and mortality would increase our understanding of the behavior of the stock
and provide confirmation of the results of the current models.
Models that incorporate environmental variables and changes in life history
parameters and recruitment would be especially useful.
Methods for age determination from length and ontogenetic stage information
could be developed for use in age-structured models.
Further investigation of complex life history changes that affect the behavior
of the population, e.g., changes in transition size/age, fecundity, or natural
mortality is necessary.
The role of compensation (such as when reproduction increases when a population
gets too low) and/or depensation (such as when reproduction declines when a
population gets low) in the regulation of shrimp populations needs to be