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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 second in a monthly series that will summarize the results of those meetings.
The soft-shell clam (Mya arenaria) fishery had a landed value of $11.2 million in Maine in 1999 and an estimated economic value to the state of $21 million. There were 2,100 commercial clam licenses. Historically, clam abundance has experienced large swings. Clam landings started to drop in 1977 and then more significantly in 1987. Clam abundance in the eastern part of the state was very low during the last nine years, but is, for reasons that are not well understood, beginning to rebound.
Sixty-eight people attended the soft-shell clam meetings that were held May 4 at the DMR laboratory here and May 17 at the University of Maine at Machias. Topics and presenters included: enhancement (Ken LaValley, Spinney Creek Shellfish Inc., and Dr. Brian Beal, University of Maine at Machias); predation (Dana Wallace, retired, DMR, and Beal); habitat (Anne Simpson, graduate student, University of Maine, and Dr. Les Watling, University of Maine); and assessment (Chris Heinig, MER Assessment Corp.).
The dominant themes of both meetings were the importance of very local, site-specific investigation and the fact that collaboration with diggers and town committees provides a mechanism for such study. The following five priority research areas were identified in the meetings.
Nearshore oceanography and clam biology. Conditions on flats within a single cove can vary widely. In order to understand the mechanisms that operate on soft-shell clam behavior and population structure, research on water currents, salinity, nutrients, and sediment must be done at the level of individual coves.
Participants identified the need to know the broodstock source for the clam larvae that settle in a specific cove. What are the oceanographic and sediment conditions that result in successful growth of clams after spat fall or reseeding? There is a need to document and explain local variability in clam growth rates, particularly the slow growth in eastern Maine.
Ecology and habitat. It is impossible to look at clams outside of a complete examination of their habitat: the structure and chemistry of mud itself, the impact of pollution on flats, the role of green algae, and the interactions with other species and fisheries.
Research questions focused on the role of the clam flat in coastal ecology and the environment, the impact of harvesting methods on the ecology of the clam flat (pulling, turning over mud, clam digging, worm digging, nearshore dragging), the impact of water quality, toxics, and exotics such as Enteromorpha on clam flat health, and the specific habitat needs of clams.
There is a need to link natural history observations with science to discover the mechanisms that control clam settlement, survival, and growth.
Enhancement. Clam enhancement encompasses a spectrum of activity. It can mean adding brush, rocks, or other structures to the flats to enhance wild spat fall, moving small wild clams to high growth or clean water areas, planting hatchery seed, or pounding legal clams for sale at better market prices.
Each of these activities raises questions about local circulation patterns, the chemistry and make-up of the mud, and the growth rates and behavior of clams at various life stages.
Clam reseeding needs to be evaluated in a statistically sound manner with evaluations of small areas (e.g. one acre). The economic viability of clam reseeding should be evaluated.
A guide for determining the optimal time for clam reseeding dependent on local conditions needs to be developed. Development of a production model would give guidance about how many clams you need to move or reseed in order to get a certain yield in the future, factoring in natural and fishing mortality.
Predators. Clams have numerous predators such as moon snails, ribbon worms, bloodworms, sand worms, green crabs, Japanese crabs, and horseshoe crabs as well as seagulls and ducks. The clam disease, neoplasia, was also discussed.
Discussion of predators included very pragmatic approaches: information sharing about predator population levels along the coast, destruction or commercial harvest of predators, destruction of their habitats such as destroying green crab burrows, and releasing sterile males into predator populations.
Research needs included the creation of markets for green crabs, moon snails, and even milky ribbonworms. The impact of human activities (digging, dragging, water quality) on population levels of clam predators needs to be evaluated. Participants proposed investing in developing better predator control methods such as green crab fences and nets. There is a need to develop collaborative tracking of predator abundance.
Assessment. Clam assessments are done at the town level to determine allocation of rights to fish. The conditions that contribute to the accuracy of an assessment -- such variables as growth rates and natural mortality -- are highly variable, even within town boundaries. Improvements both of survey techniques and of the assumptions that go into the model about growth and natural mortality were discussed. However, especially given the expense of assessment, participants placed highest priority on developing ways to survey and ground truth surveys working with diggers to enhance the credibility and usefulness of assessments.
Priority research needs are to improve the clam assessment survey methods working with diggers, develop seasonal and regional clam volumetric ratios and/or length/weight ratios, and develop clam growth rates for different areas using volunteer sampling cove-by-cove.
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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