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Feature Articles
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Northern shrimp: Setting research agenda
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This article is reprinted with permission of Commercial Fisheries News, the Northeast's fishing newspaper for over 30 years, ©2003 Compass Publications Inc. Commercial Fisheries News is published monthly; annual subscriptions are $21.95. To subscribe or request a sample issue: call (877) 263-4496; fax (207) 367-2490; e-mail (cfoster@fish-news.com); or click on the hot link.
WEST BOOTHBAY HARBOR, ME - In May 2000, the Department of Marine Resources (DMR) undertook a research agenda-setting effort for five of Maine's major commercial species: clams, lobsters, scallops, sea urchins, and shrimp. The following is the third in a monthly series that will summarize the results of these meetings. (Sea urchins were covered on the DMR page in the CFN April 2001 and clams in CFN May 2001.)
Northern shrimp, Pandalus borealis, had a landed value of $3.65 million in Maine in 2000. The fishery is conducted by drags and traps, for which a total of 555 licenses were issued in 2000.
The shrimp resource is managed by the DMR, which participates with New Hampshire and Massachusetts in the Atlantic Marine Fisheries Commission's (ASMFC) Northern Shrimp Section's shrimp plan.
The plan establishes a season of 183 days maximum between Dec. 1 and May 31, sets a 1-3/4" minimum mesh size in the body of the net and cod end, and requires use of a Nordmore grate to reduce bycatch of finfish. The season length is set each year based on summer shrimp stock assessment surveys and advice from the industry advisers.
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.
Meeting
Twenty-nine people attended the shrimp meeting that was held May 12, 2000 at the DMR Laboratory here. Topics and presenters included: Stock Assessment -- Mike Armstrong, Massachusetts Division of Marine Fisheries; Oceanography -- David Townsend, University of Maine; Life History -- Dan Schick, Maine DMR; and Economics and Gear -- Amy Schick, ASMFC.
The focus of the shrimp discussion was on understanding the underlying mechanisms of oceanography and shrimp biology and behavior that affect the shrimp population.
The following priority research areas were identified in the meeting.
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Shrimp life history and behavior. Much is still unknown about the basic biology and behavior of northern shrimp. Little is known about timing, release, and subsequent behavior of shrimp larvae or how long a shrimp is a juvenile, 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 include determining 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?
A description of shrimp juvenile life history, especially its duration, is needed 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 maturation (male)?
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Effects of large-scale oceanographic events on shrimp. It has long been known that shrimp are highly sensitive to temperature. Modern oceanographic tools are providing us with a much more sophisticated understanding of the Gulf of Maine'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 meters) 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 to 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, and to evaluate the physical and biological effects of oceanographic events relative to the shrimp population.
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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 to conduct objective, collaborative research on the effect of shrimp trawl gear on benthic habitats, substrate, and animals; determine if shrimp have any refuges from gear in the Gulf of Maine and, if so, what is their significance to the shrimp population; and continue conservation engineering for shrimp traps and trawls as needed to meet changing fishery conditions and new knowledge.
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Access issues. 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 multispecies 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.
Research priorities are: develop and evaluate options for multispecies 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; and 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.
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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 adviser 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.
The research priorities is to 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.
A copy of the research priorities can be found on the DMR page at http://www.state.me.us/dmr/ or by contacting Naomi Petley, DMR Laboratory, PO Box 8, West Boothbay Harbor, ME 04575; call (207) 633-9525; or e-mail Naomi.Petley@state.me.us.
This 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; and staffed by the GMA consultants, DMR, and the University of Maine Marine Extension Team.
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