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(Pandalus borealis)  

Prepared by the 
Gulf of Maine Aquarium 
January 10, 2001

Table of Contents 




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 results.  

Robin Alden
Don Perkins
Gulf of Maine Aquarium




NORTHERN SHRIMP (Pandalus borealis)  

I.  Background 

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. 

Shrimp populations 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

These Northern 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. 

Establishment of 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.


III.  Methodology

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. 

Meetings 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.  


IV.  Shrimp 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 
2.  Oceanography                 David Townsend, Ph.D., University of Maine                      
3.  Life History                      Dan Schick, DMR
4.  Economics and Gear        Amy Schick, Atlantic States Marine Fisheries Commission 

Twenty-nine people 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 shrimp.


V.  Shrimp Report Format

Results of the meetings are presented in two different formats: 

1)      Priorities voted by the group (Section VI) which are presented with context; and

2)      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 study.  


VI.  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.


Shrimp Priority 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. 

Research priorities are:

a)      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 class strength?

b)      Describe shrimp juvenile life history, especially its duration, to provide better assumptions for stock assessment models. 

c)      What factors regulate timing of juvenile shrimp migrations, sexual transformation (male to female) and female inshore/offshore migration?

d)      What factors such as density dependence are operating to determine shrimp sexual maturation (male)? 

“Juvenile 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?” 

Daniel Schick

Attachment B


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 shrimp.

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.  

Research priorities are: 

a)      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 Maine.

b)      Evaluate the physical and biological effects of oceanographic events relative to the shrimp population.


Shrimp Priority 3:  Habitat and Gear

Habitat issues 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. 

Research priorities are:

a)      Conduct objective, collaborative research on the effect of shrimp trawl gear on benthic habitats, substrate, and animals.

b)      Do shrimp have any refuges from gear in the Gulf of Maine and if so, what is their significance to the shrimp population?

c)      Continue conservation engineering for shrimp traps and trawls as needed to meet changing fishery conditions and new knowledge. 

“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 mesh exemption area?” 

Amy Schick

Attachment D


Shrimp Priority 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. 

Research priorities are:

a)      Develop and evaluate options for multi-species management that considers the interests of all Maine shrimpers and gear types.

b)      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.

c)      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 entry.


“Models that incorporate environmental variables and changes in life history parameters and recruitment would be especially useful.”  

Michael P. Armstrong, Ph.D.

Attachment E


Shrimp Priority 5:  Communication and Collaboration in Shrimp Assessment

Communication and 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. 

Research priorities are:

a)      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. 


VII.  Shrimp Observations and Questions from Discussion

Assessment Models

Incorporate into 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?

Separate the estimate of natural mortality from fishing mortality.

Provide industry with predictive information by understanding the relationship of population size to availability to the fishery.

Further investigate the apparent direct parent/progeny relationship in the population.

Develop biological reference points that are flexible, able to be changed based on updated information.

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 this shift.

Put information about the development of the ASMFC shrimp plan on the Web for easy access by industry.

Collaborative gear/habitat work to make it credible, objective.

Environmental Issues

What are effects of the chlorine in sewage outflows on plankton, and thus on shrimp? Cite work done on Maine Yankee in 1970s.


Nordmore grate 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?

Would protected areas help the shrimp population?

What is the efficiency of traps at different times of year?

Life History

What determines egg drop?  Why was it early in 1999-2000 season?

Need better understanding and estimate of natural mortality.

Role of predators in shrimp populations.

Role of 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?

Could environmental conditions at time of larval release be used as predictor of year class strength?

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 than that? 

Research juvenile 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?

Does sexual 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 Basin.

What cue triggers transition from male to female?  A hormone? 

Does stock size influence sexual differentiation? 

Understand the 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 design?

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 larval success?

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?

Limited Entry

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.

Using historical 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 aggregation? 

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 temperature?

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?


Temperature and 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.

Europeans measure 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.

Correlate North 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.

Link oceanographic information and the population spatially because populations move.

Research links between the oceanography and the life history stages (temperature, food availability, currents)

Use historical data from many sources -- NMFS groundfish surveys, cloud cover, etc. in developing relationships between oceanography and shrimp population.

Stock Structure

Is Maine's shrimp stock part of a larger stock we don't have much control over or is it an isolated population?

Relationship of larvae from eggs released in one area on shrimp in another. 

Is larval supply from local stocks?

Survey Techniques

Improve ability to catch/classify larvae and use larval surveys to get an early indication of year class strength.

Get industry 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?

Should temperature be included in trawl survey experimental design?  If so, should bottom temperature or surface temperature be used?


Attachment A:




May 12, 2000 at DMR Laboratory, W. Boothbay Harbor 

29 Participants 

Mike Armstrong             MA. Div. of Marine Fisheries, Gloucester              978-282-1435

Dick Bridges                 P.O. Box 27, Sunset 04683                                  348-2840

David Townsend            U Maine, Orono                                                   581-4367

Amy Schick                 Atlantic States Marine Fisheries Commission         202-289-6400

Josef Idoine                  NMFS/NEFSC, Woods Hole, MA                          508-485-2217

Kilo Pinkham                F/V Jeanne C                                                      633-6315

Bill Sutter                     P.O. Box 109, Wiscasset 04578                           882-7230

Maggie Hunter              DMR, Boothbay Harbor                                         633-9550

Art Mayers                   Lincoln County News                                            563-3171

Dale Moore                  New Harbor                                                            

Bill Sherman                Southport

George Richardson       6 Jewett Cove Rd., Westport 04578                       882-6270

James Fossett             Pemaquid                                                            677-3689

Dan Schick                  DMR, Boothbay Harbor                                         563-5786

Dale Prentice               P.O. Box 25, Bristol 04539                                    563-3576

Butch Thompson          P.O. Box 176, Port Clyde 04855                            372-8831

Russell Brewer            102 Townsend Ave., Boothbay Harbor 04538            633-2520

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                     729-3793

Joho Seiders               8 Sunset Coop, S. Bristol 04568                              644-8449

Les Watling                 UM Darling Marine Center, Walpole 04573               563-3146 x248

Anne Simpson             UM Darling Marine Center, Walpole 04573               563-3146 x254

Ed Gastalch                P.O. Box 289, New Harbor  04554                           677-2964

Linda Mercer               DMR, Boothbay Harbor                                           633-9525

Paul Anderson             Sea Grant/UM Cooperative Extension                      581-1422

Dana Morse                 Sea Grant/UM Cooperative Extension                      563-3146 x205

Sherman Hoyt              Sea Grant/UM Cooperative Extension                      800-244-2104

Robin Alden                 PO Box 274, Stonington 04681                               367-2473   


Attachment B: 

Life History the Northern Shrimp in the Gulf of Maine 

Daniel Schick, Maine Department of Marine Resources 

Maine DMR Coastal Fishery Research Priority Meetings 

May 12, 2000



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.

Life History:

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.

The prior 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:

  1. Larval distribution and survival 

a.       Timing of larval release progresses from west to east along the coast.  Why does this occur and can this be used in management?

b.      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?

c.       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? 

  1. Juvenile life history

a.       Black box.  Nothing is known about the juveniles.

b.      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. 

  1. Juvenile migration offshore

a.       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? 

  1. Age at sexual maturation: male

a.       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 Jeffreys Basin.

  1. Timing of transition

a.       Late fall to spring:  What drives the timing of the change? 

  1. Female migration inshore and back offshore

a.       Timing of approach to shore:  What drives this migration?

b.      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?

c.       Timing of leaving shore:  The females leave shore one week to two weeks after larval release.  Is this timing only related to larval release?

d.      Timing of reaggregation offshore:  This seems to occur in mid-May, but does this vary in time and space? 

  1. Timing of first molt after egg hatch

a.       Seems to occur as females start their offshore migration.

b.      How long does this process take and how long is it until the new shells are hardened again?

c.       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? 

  1. Fecundity

a.       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? 

  1. Early maturing females

a.       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? 



Attachment C: 

How the Oceanography of the Gulf of Maine Can Vary 

(and why that might be important to shrimp and other marine resources) 

David W. Townsend, Ph.D., University of Maine 

Maine DMR Coastal Fishery Research Priority Meetings

May 12, 2000 


Attachment D: 

Northern Shrimp Policy, Economics and Gear 

Amy Schick, Atlantic States Marine Fisheries Commissions 

Maine DMR Coastal Fishery Research Priority Meetings 

May 12, 2000 

Gear - Current Uses 

▪      Management tool

      ▫     Mesh size
      ▫      Nordmore grate
      ▫     Double Nordmore grate
      ▫     Cod end strengthener 

Gear - Application 

      ▪     Minimize bycatch
      ▫     non-target species
      ▫      appropriate shrimp life stages
   ▪      Characterize bycatch beyond the small mesh exemption area 

Gear - Questions 

      ▪     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 mesh exemption area? 

Economics - Current Uses 

      ▪     Descriptive information
      ▫     market conditions
      ▫     price of shrimp
      ▫     ex-vessel value 

Economics - Application 

      ▪     Market conditions
      ▫     Product flow and utilization
      ▫     Price
      ▪     Costs-benefits of fishing
      ▪     Incorporate economics into the stock assessment
      ▪      Characterizing demographics 

Economic – Questions 

      ▪     When is harvesting most profitable?
      ▪     How do market conditions influence harvest?
      ▪     How does the interaction with other fisheries influence the decision to fish for shrimp? 

Management - Application 

      ▪     Risk analysis and uncertainty
      ▪     Biological reference points
      ▪      Environmental conditions
      ▪     Predictive  modeling
      ▪      Development of bio-economic model
   ▪     Interaction of the shrimp fleet with other fisheries 

Management - Questions 

      ▪     How can risk and uncertainty be better characterized?
   ▪     What influence do environmental conditions have on northern shrimp abundance and distribution?   


Attachment E: 

Stock Assessment of Northern Shrimp in the Gulf of Maine 

Michael P. Armstrong, Ph.D., Massachusetts Division of Marine Fisheries 

Maine DMR Coastal Fishery Research Priority Meetings 

May 12, 2000 

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:  

1.   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);  

2.   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 abundance;   

3.      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 be improved:  

      ▪     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 explored.


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