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     DEPARTMENT OF MARINE RESOURCES

 
COASTAL FISHERY RESEARCH PRIORITIES 

SOFT-SHELL CLAMS 

(Mya Arenaria) 

Prepared by the
Gulf of Maine Aquarium
January 10, 2001


Table of Contents 


    

Acknowledgements 

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 

 

MAINE DEPARTMENT OF MARINE RESOURCES

 COASTAL FISHERY RESEARCH PRIORITIES

SOFT-SHELL CLAMS (Mya Arenaria) 

 

I.  Background 

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. 

Clamming is restricted to hand harvesting, with the exception of transplanting operations done by municipalities.  Clamming while diving is prohibited.  There is a statewide 2" minimum size.  The state conducts an extensive public health monitoring effort for clam flats.  Samples are examined for bacterial pollution and toxic algae on an ongoing basis and those flats that are classified as conditional are opened and closed based on rainfall.

Authority for managing the soft-shell clam fishery lies with the State of Maine and is delegated by the Commissioner of the Department of Marine Resources under certain conditions to municipalities.  There are 65 towns under town management out of 110 towns with intertidal flats.  A state commercial shellfish license is required for commercial harvesting and towns that have shellfish ordinances require town licenses.  Towns form Shellfish Conservation Committees and are authorized to raise money to cover enforcement and enhancement.  They are allowed to limit the number of commercial diggers with a ratio of not less than 10% non-resident diggers.  Many town shellfish committees require diggers to put in conservation time as a condition for holding a license.  This can include attending meetings and participating in reseeding efforts. 

The Maine Soft-shell Clam Council is made up of town officials, town shellfish committees, dealers, diggers, aquaculturists, and state managers.  It provides a forum for discussion of clam issues. 

   

II.  DMR Research Priorities Project

These clam 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 the 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, however, will accomplish several other goals.  First, by establishing and communicating a shared vision of comprehensive research needs, it will stimulate the 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 should 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 project was staffed by the GMA consultants, DMR, and the University of Maine Marine Extension Team. 

   

III.  Methodology

At least one, all-day meeting was held for each fishery.  The meetings were designed to be non-regulatory, neutral, and inclusive following a format developed by the GMA in previous efforts for other species. The meetings brought together fishermen, academic scientists, government scientists, non-governmental organizations, 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.  Each of the presenters was 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 of the sessions was the same.  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 a selected topic and on his or her major research questions about the species.  The group then 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.  Clam Research Priority Meetings

Two clam meetings were held:  May 4, 2000 at the DMR Laboratory in West Boothbay Harbor, ME, and May 17, 2000 at the University of Maine at Machias.  Both meetings were held from 9 a.m. to 5 p.m.  Topics and presenters included:

May 4: 

1.  Enhancement        Ken La Valley, Spinney Creek Shellfish, Inc. 
2.  Predation              Dana Wallace, retired, Maine Dept. of Marine Resources
3.  Habitat                  Anne Simpson, Graduate Student, University of Maine
4.  Assessment          Chris Heinig, MER Assessment Corp. 

May 17: 

1.  Enhancement         Dr. Brian Beal, University of Maine at Machias 
2.  Predation               Dr. Brian Beal, University of Maine at Machias
3.  Habitat                   Dr. Les Watling, University of Maine
4.  Assessment           Chris Heinig, MER Assessment Corp. 

Forty-three people attended the May 4 meeting at the DMR laboratory and 25 attended the May 17 meeting at University of Maine at Machias.  Attendees included clammers, town officials involved in town clam conservation committees, DMR managers and biologists, the mussel industry, several consultants, and researchers from the University of Maine, University of Maine at Machias, and Maine Maritime Academy. 

   

V.  Clam Report Format

Results of the meetings are presented in two different formats: 

1)  The 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 meetings.  The priorities organize thought and focus effort.  The details are essential because it is the local observations and questions that provide the raw material of good scientific hypothesis.  Although the clam meetings were divided into four segments:  Enhancement, Predation, Habitat, and Assessment, the report is not structured around those categories except where it makes sense.  Many topics, such as oceanography, growth and reproduction 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 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

The clam meetings produced a particularly rich set of questions and observations.  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.   

   

Clam Priority 1:  Nearshore Oceanography and Clam Biology 

The soft-shell clam is a difficult animal to study.  It is intertidal, subject to many different environmental stresses, and many predators.   More than any other important commercial species, clams require fine scale, site-specific research.  Clammers, clam biologists, and sediment scientists all understand that conditions on flats within a single cove can vary widely.   In order to develop an understanding of the mechanisms that operate on soft-shell clam behavior and population structure, research on currents, salinity, nutrients, and sediment must be done at the level of individual coves.  The close observation that diggers do, working a specific set of flats over many years, provides a source of natural history information that could be very important in deciphering the underlying mechanisms of clam populations.  

Priority research needs are: 

a)   What is the broodstock source for the clam larvae that settle in a specific cove?

b)   What are the oceanographic and sediment conditions that result in successful growth of clams after spat fall or reseeding? 

c)   Document and explain local variability in clam growth rates, particularly the slow growth in eastern Maine.  

   

Clam Priority 2:  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. The discussion clearly pushed toward multi-species, intertidal studies that go beyond the pursuit of information about a single species such as clams. 

Priority research needs are: 

a)   What is the role of the clam flat in coastal ecology and the environment? 

b)   What is the impact of harvesting methods on the ecology of the clam flat:  pulling, turning over mud, clam digging, worm digging, nearshore dragging?

c)   What is impact of water quality, toxics, and exotics such as enteromorpha on clam flat health? 

d)   What are the specific habitat needs of clams?

e)   Link natural history observations with science to discover the mechanisms that control clam settlement, survival, and growth. 

   

Clam Priority 3:  Enhancement

Clam enhancement provides a lens to focus a number of basic research questions about clam biology, nearshore oceanography, and the mud clams live in (benthic ecology).  The term clam enhancement actually 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, the growth rates and behavior of clams at various life stages. 

Priority research needs are:

a)   Evaluate clam reseeding in a statistically sound manner with evaluations of small areas (e.g. 1 acre.)

b)   Evaluate the economic viability of clam reseeding.

c)   Develop a guide for determining the optimal time for clam reseeding dependent on local conditions.

d)   Develop a production model that 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. 


“For soft-shell clams in Maine, enhancing wild stocks has been practiced in communities by clammers for more than a half a century.”   

Brian Beal, Ph.D.

(Attachment B)

“Clam enhancement activities should be a combination of hatchery reared/transplanted seed and enhanced natural recruitment, in order to maximize growth before planting and overwintering survival”.  

Kenneth J. La Valley

(Attachment C)

   

Clam Priority 4:  Predators

Clams have numerous predators that include a range of organisms.  The group specifically named moon snails, ribbon worms, blood worms, sand worms, green crabs, Japanese crabs, horseshoe crabs as well as seagulls and ducks.  They also discussed the clam disease, neoplasia.  Each presents a different challenge to clammers and managers.  The green crabs and moon snails function on top of the mud and, at least for the crabs, may be vulnerable to physical barriers.  The milky ribbonworm, however, eats from below taking both juvenile and adult clams. 

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. The discussion also approached predators from a population biology and ecology point of view with questions about the life history and the role of human activities in enhancing or discouraging the growth of predator populations.

Priority research needs are:
        a)      Create a market for green crabs, moon snails, and even milky ribbonworms. 

        b)      Evaluate the ways that human activities (digging, dragging, water quality) impact the population levels of clam predators?

        c)      Invest in developing better predator control methods such as green crab fences and nets.

        d)      Develop collaborative tracking of predator abundance.


“We do not understand what controls population numbers of moon snails or the relationship (if any) between snail size (or age) and fecundity.  Snails at some intertidal sites appear to increase in size with decreasing tidal height, but on others, they remain small throughout the intertidal zone; why is this?”  

Brian Beal, Ph.D.

(Attachment D) 

“The state may face serious green crab problems again.  Between 1990 and 1999 the temperature again climbed to an average of 48.5 F.”  

Dana Wallace

(Attachment E)

   
Clam Priority 5:  Assessment

Clam assessments are currently used to make the most difficult fishery management decisions:  allocation of rights to fish.  This is done at the town level, where things are local, personal, and highly visible.  This puts tremendous pressure on the methods and credibility of clam assessment techniques.  Furthermore, 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:

        a)      Improve the clam assessment survey methods working with diggers. 

        b)      Develop seasonal and regional clam volumetric ratios and/or length/weight ratios. 

        c)      Develop clam growth rates for different areas using volunteer sampling cove-by-cove.


“Mortality has multiple components, including direct harvest mortality or “take”, harvest-associated mortality, e.g. suffocation due to burial or exposure, predation, and natural attrition.  These are very difficult to ascertain accurately and, as with growth, will vary considerably from one location to another.  Nevertheless, despite the complexities, such projections may be essential if proper management is to be achieved in the future.” 

Chris Heinig

(Attachment F)

   

Additional topics:

The scientific requirement of fine scale investigation dovetails with another major theme of the two clam meetings.  Local diggers and clam committees made clear their desire for a process that would allow them responsive help turning their questions about their flats into answers -- good research and good stewardship.  Discussion about the role of DMR's area biologists revealed that clam committees would like to see DMR provide on-the-flats collaborative scientific help.  Clam committees also want better communication among towns to share research approaches and experience, and ideas.  There was some discussion about better use of the Maine Soft-shell Clam Council structure to meet these needs.  Finally, there was interest in finding ways to reward diggers and townspeople that do good stewardship of the flats. 

At the Boothbay Harbor meeting, the group identified a triangle that included three factors for good clam management and research:  information exchange, collaborative research, and leadership development.  When the three factors were ranked, better information exchange stood out as the immediate, threshold need.  The group wanted to form a committee from those at the meeting to raise the visibility of clam issues, get funding for clam research and start collaborative work that would include diggers, town committees and scientists.  

   

VII.  Clam Observations and Questions from Discussion

Assessment and Surveys

Growth and mortality are the two primary assumptions in the clam assessment model.  Improving these estimates and making them regional or local is important. 

Validate the survey methodology by doing a post-survey harvest count and compare it to survey estimates, both immediately after the survey and one year or each year following the survey.

Develop an alternative, simpler yet adequately accurate methodology.

Develop regional estimates for growth rate (incremental/annual) and the various components of mortality.

Clam landings continue to be underreported.

Develop a correction factor to make the landings data more reliable. 

Clam landings are collected by town and this does not provide the detail on a cove-by-cove basis that is useful in clam management.  It would be helpful, but probably impossible, to get information at that level.

How could assessments be made more useful to towns in indicating the value of the fishery to the town?

Recalculate the volumetric conversions that are used for clams.  Examine the way this ratio changes seasonally.  Would it be preferable to use length/weight ratios instead?

Evaluate the significance of differences between clams from different habitats. 

Refine sampling procedures for surveying flats. 

Develop a procedure for assessing recruits in November, December, or January when the new year class of clams is visible.

Should a survey of other organisms (predators, periwinkles, enteromorpha, mussels) be included in the standard survey procedure?

Develop an intertidal ecosystem survey approach.

Communication

Diggers and clam committees need help understanding how to work with the Army Corps of Engineers’ rules for permits for structures on flats.

Need leadership from the state -- especially the DMR Area Biologists --  in coordinating towns, state, diggers, and research community.

Re-examine the role of area biologists.  They should conduct or stimulate research on problems of concern articulated by diggers and towns.  They can perform role in linking the observations of diggers with scientists.

Use study of the flats to help get clammers and wormers talking with each other.  This is difficult given that wormers perceive the town ordinances to be unfair to them.

Use study of the flats also to help get clammers and wormers to talk with mussel draggers.    This works best if it is not in a situation where a regulation is being considered. 

   

Disease

What is inducing neoplasia on flats? 

Need method for rapid assessment of the disease.

Ecology

What is the impact of a clam flat on the ecology of the environment?  Are there significant environmental benefits to sustaining soft-shell clam populations?

Is there any way to test the mud and determine whether or not it will support clams?

Is there a succession of clams and other bivalves on a flat?  Is there a succession of predators? 

What is the ecological role of the ribbonworm? 

Look at historical data on cycles of clams and flat ecology to develop understanding about what is realistic to expect now. 

Use areas that are closed to digging and/or dragging as control sites. 

What are the effects of clamming, worming, and mussel dragging on each of the other two fisheries?

What is the impact of inter-tidal and nearshore dragging on the ecology of specific types of flats?

Since the 1998 big mussel set, we appear to be in a high mussel period.  What is the dynamic relationship between mussels and clams? 

Environmental Issues

Monitor the chemistry on the bottom and in the water for heavy metals, pesticides, and other forms of pollution.

What is the transport of Velpar in nearshore environments? 

What is the timing of Velpar's presence in clam habitats since its effects differ at different life cycle stages?

Metals bind to mucus and things on grains of sediments when they are buried in flats.  Are they bio-available at that point?

What is the cumulative effect of heavy metals on clam reproduction?

Do clams accumulate heavy metals, Velpar?

Habitat

What is the effect of digging on clam habitat and health of the flats in different sediment types and oceanographic conditions?  Can a flat be "over-dug?"   Can this information result in recommendations for flat rotation?

Document the actual pattern of soft digging:  where are diggers, how many, etc.

If mud is too loose, you need to turn it over.  Can't expect something to grow fast in mud that doesn't push against it.  For seven years I have worked a 30-acre flat with mud so soft you would step down to your calf, just turning over the mud.  Have changed consistency of mud and greatly enhanced my digging.

Some are concerned that wormers are turning mud too much;  others like idea and believe it enhances recruitment.

What are the site-specific issues behind the mud-turning questions -- substrate, hydrography, and more? 

Pullers don't turn the mud; may have long term adverse impacts.

Why do waterholes collect spat?  Understand how they work and recreate them to help effective spat fall. 

How do sediments influence clam fecundity?

What is the relationship of tidal height effects to fecundity?

Document the extent of enteromorpha in Maine, possibly with aerial surveys and Geographic Information System (GIS) mapping. 

What is enteromorpha's life cycle?  What is its relationship to clam populations, periwinkle populations and nutrient loading?  What other green algae do we have?

Why are juvenile clams associated with enteromorpha?

What is the impact of green crabs' burrowing activity on oxygen content of flats?

Life History

Why do Cobscook Bay clams grow so slowly?

Are low growth rates found only in Washington County?

What does history show?  Have growth rates downeast always been slower than other parts of the state?

What triggers effective spawning?

What is the relative egg and sperm production of large and small clams? 

What is the impact clam of the change in harvesting technique to "pulling?"  What is the impact of the 2" law?

What is required for successful fertilization?

What makes a mud flat suitable habitat for clams to set in it? 

How do clams select a site to settle? 

What is needed for successful spat fall?

Does downeast Maine have a real problem with supply of larval seed? 

What happens to a clam larva when it leaves the plankton stage?  What does it attach to?  Does it need a particle of a specific size?

Need to understand from a mechanistic point of view the sediment and food requirements of juvenile clams.

What is the importance of suspended sediment in reducing growth rates?

Continue work in documenting whether collecting clam spat works.

Management

Would clam spawning sanctuaries be a good tool?

How can a digger reduce mortality rate of clams left behind?

Mussels

Develop a code of practice for mussel harvesters to ensure industry is environmentally sustainable.

Develop database about interactions with mussel farming and other marine species.

Study ecological interaction between mussel beds of many types (undisturbed, selectively harvested, bottom farmed, and raft farmed) and other species including fish, invertebrates, and birds.

Oceanography

Where are the parent stocks located?  Where do juvenile clam sets originate?

What are the circulation characteristics of a successful clam flat?

Predator Control

Does human activity (digging, dragging, water quality) impact the population levels of predators?

Reestablish the DMR program of Shore Searches for crabs of all sizes using standard procedures.  This program was carried on all along the coast from 1973 to 1985.

Explore gametogenesis and effects of temperature on green crab survival.

Research improved netting and fencing models to be more effective and demonstrate economic advantages and limitations. 

Do a population assessment of moon snails and green crabs. 

Study the life history and population dynamics of snails that are clam predators including the role of salinity in snail population control and behavior.

Is it possible and/or feasible to collect enough moon snails and egg collars to reduce their population enough to benefit clams?

What controls the population of moon snails.  Is there a correlation between size and fecundity? 

Quantify clam predation by fish and birds.

Explore the dynamics of the Japanese crab invasion on Cape Cod where they have destroyed the green crab population.

Develop a market and fishery for green crabs. 

What preys on green crabs?

What are the environmental conditions that favor specific predators?

How can we destroy the juvenile green crab, before putting down predator nets?

How far down are ribbon worms found in the sediment? 

Study attractants for green crabs and moon snails (mayonnaise)?

Study the effect of digging and flat rotation on predator levels. 

Reseeding

Do formal evaluations of the effectiveness of reseeding.

Do formal, credible study to document the survival rate of hatchery seed transplanted. 

Determine the best time for planting reseeded clams.  Each area appears to be different.  Some say fall; some say spring; all say timing is critical.  Determine parameters important to this decision for different habitats.

Socio-economic Issues

Access to mud is difficult in many towns, now.

Develop a market for green crabs.


   

Attachment A: 

SOFT-SHELL CLAM RESEARCH PRIORITIES 

MEETING ATTENDEES 

May 4, 2000 at DMR Laboratory, W. Boothbay Harbor 

44 Participants

Guy D. Watson   1019 Sligo Road, No. Yarmouth   829-4363 Laura Livingston   DMR Boothbay Harbor   633-9533 Stephen Fegley   ME Maritime Academy, Castine 04420   326-2396 Jon Heintz   HC 33 Box 1474, Georgetown 04548   371-2732 Alan Houston   28 Federal St., Brunswick 04011   725-6639 Robert Wixted   29 Bouchard Dr., Brunswick 04011   721-8974 Ken La Valley   25 Stevenson Rd., Kittery 03904   439-2719 Dana Wallace   1036 Mere Pt. Rd., Brunswick 04011   725-4557 Arthur Dodge   98 HH Road, Harpswell 04079   721-0651

  • Steve Barnes   PO Box 160 Bremen   529-2447

  • Frank E. Perkins Sr.   21 Bay St., Boothbay Harbor   633-3555

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

  • Rep. Ken Honey   PO Box 6, Boothbay 04537   633-5560

  • Cindy Gagno   175 Lowellton Rd., Wiscasset 04578   882-9256

  • Carol A. James   Box 438 Willow Lane, Wiscasset 04578   882-6742

  • Phil Yund   Darling Marine Center, Walpole   563-3146 x217

  • Jim Hennessey   Hennessey Rd., West Bath   443-9435

  • Jeff Armstrong   18 Avon Rd., Cape Elizabeth 04107   799-7193

  • Lockwood Chamberlin   278 Maine St., Brunswick 04011   721-9377

  • Donald R. Berthiaume   Biddeford High School, PO Box 482A, Kennebunkport 04046   282-1596 (w) 
    967-0032 (h)

  • Erik Wvori   1070 Main Rd., Islesboro 04848   734-8859

  • Annie Bolduc   PO Box 243, Islesboro 04848   734-6511

  • Sue Watson   Time and Tide RC&D, 9 Green St.,  Augusta, 04530   622-7847 x4

  • Paul Waterstrat   DMR PO Box 8, Boothbay Harbor 04575   633-9560

  • Dana Morse   UM Darling Marine Center, Walpole   563-3146 x205

  • David Clifford   P.O. Box 37, East Machias 04630   255-3926

  • David Sutter   271 Federal St., Wiscasset 04578   882-7070

  • Robert Goodwin   DMR, Lamoine Lab   667-5654

  • Chip Davison   Great Eastern Mussel Farms, PO Box 141, Tenants Harbor 04860   372-6317

  • John White   5 Fairfield Dr., Kennebunk 04043   967-4758

  • Carolyn Skinder   33 Margin, Orono 04473

  • Sherry Hanson   DMR, Boothbay Harbor   633-9401

  • Richard LeMont   24 Lemont Way, Phippsburg 04562   389-2105

  • Hal Winters   DMR, Augusta   624-6562

  • Linda Mercer   DMR, Boothbay Harbor   633-9525

  • Chris Heinig   MER 14 Industrial Parkway, Brunswick 04011   798-7935

  • Dan Devereaux   28 Federal St., Brunswick 04011   725-6631

  • Bruce Chamberlin   DMR   525-3555

  • Kim Payne   Normandeau Assoc. 251 Main St., Yarmouth 04096   846-3598

  • Don Card   DMR   443-2793

  • Lisa Cote   DMR, Augusta   624-6550

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

  • Don Perkins   Gulf of Maine Aquarium, PO Box 7549, Portland 04112   871-7804

  • Robin Alden   PO Box 274, Stonington 04681   367-2473 

 

May 17, 2000 at University of Maine at Machias 

25 Participants 

Stephen Fegley            ME Maritime Academy, Castine 04420         326-2396
Arthur Dodge                98 HH Road, Harpswell 04079                      721-0651
Rep. Martha Bagley      Machias 04654                                           255-6567
Paul Thompson            Pembroke 04666                                         726-5290
Jane Hinson                 HC70 Box 28, Machias 04654                      255-3851
Dana Wallace              1036 Mere Point Rd., Brunswick 04011         725-4557
Les Watling                 UM Darling Marine Center, Walpole 04573     563-3146
Darrell Richards            Roque Bluffs
Tracy Vassiliev             U Maine, 202 Rogers Hall, Orono 04469        581-2736
Will Hopkins                 4 Favor St, Eastport 04631                          853-4560
Bill Congelton               University of Maine Orono 04469
Bill Walton                   P.O. Box 83, Beals 04611                           447-5769
Brian Beal                    University of Maine, Machias                       255-1314
Jim Dow                       P.O. Box 974, Blue Hill 04614                     374-2998
Everett Johnson            RR1 Box 3120, Jonesport 04649                  487-3299
John Cox                     P.O. Box 183, Jonesboro 04648                   434-2157
Dave Clifford                 P.O. Box 37, East Machias 04630               255-3926
Gregory Biss                220 Water St. Eastport 04631                     853-4775
Chris Heinig                  MER, Harpswell                                         729-4245
Linda Mercer                 MR, Boothbay Harbor                                 633-9525
Ron Aho                       DMR
Paul Anderson              Sea Grant/UM Cooperative Extension           581-1422
Chris Bartlett                Sea Grant/UM Cooperative Extension           853-2518
Sherman Hoyt              Sea Grant/UM Cooperative Extension  (800) 244-2104
Robin Alden                  PO Box 274, Stonington 04681                    367-2473

   

Attachment B:

Soft-shell Clam Stock Enhancement
Brian Beal, Ph.D., University of Maine at Machias
Maine DMR Coastal Fishery Research Priority Meetings
May 17, 2000 

Stock enhancement is the direct and indirect manipulation of wild or cultured organisms to improve, strengthen, or augment harvests, recruitment, reproduction (fecundity), or the genes of a population.   For soft-shell clams in Maine, enhancing wild stocks has been practiced in communities by clammers for more than a half a century.  The primary goal of the vast majority of these field projects has been to increase harvests.  

Enhancement of wild stocks of soft-shell clams in Maine has been accomplished by: 

  •       Moving clams for two reasons, both of which have the goal to increase harvests within a relatively short period of time (6–18 months).  Sub-legal or undersize wild clams (“seed”) are moved from areas of high densities where growth is slow or negligible (usually near the high tide mark) to areas of low clam densities (usually near the mid to low tide mark) where growth is faster.   Clams are also moved from areas where fecal coliform levels are too high for human consumption or to areas where water quality poses no threat to human health. 

  •       Adding brush (tree boughs) to the intertidal zone to create “hydrodynamic eddies” that reduce water motion.  These low current zones give tiny (usually less than 3 mm in length), highly mobile clams living at or near the sediment surface a place to burrow in and grow with fewer chances of being eroded or washed away.  Another advantage of the brush is that it may also provide the small clams a kind of “safety net.”  That is, it may reduce the chances of a predator such as green crabs preying successfully on the small clams because it interferes with the crabs’ ability to burrow and excavate clams.  Large rocks or boulders covered with seaweed that occur on clam flats also reduce water motion.  Often, one can see many clam holes surrounding these rocks, especially on the low tide side.  In contrast, several feet away from the rock there usually are fewer holes.  Recently, some communities have used plastic netting (1/4" flexible) to protect small seed clams.  If the nets are arranged with floats or toggles so that they bulge into the water column during high tide, they will serve a very similar purpose to the brush. 

  •       Planting hatchery-reared “seed” (Mook Sea Farms, Spinney Creek, Beals Island Regional Shellfish Hatchery) that are 8–15 mm in length under plastic netting.  Typically, nets are 12-14" wide by 20-22" long, secured by digging a 6- 8" furrow around the seeded perimeter.  Clams are seeded 20-40 clams per square foot.  The edge of the net is placed into the furrow and the excavated sediments are back-filled.  On muddy bottoms, there is a need to use floats or toggles placed on the underside of the nets that will enable them to rise and fall with the tide.  This will discourage the build up of mud on top of the nets that could smother clams below. 

Impounding legal size clams during periods when per bushel prices are low (March to April) and then selling them when prices are annually the highest (August to early September).  Although this activity is not often thought of as enhancing stocks per se, the goal is to increase harvests with a concomitant benefit of adding value to the product.  If clams are handled correctly, “clam pounding” a bushel within a 12-square foot cage will result in 95% survival between April and August.  April prices per bushel are consistently less than $1.00 per pound.  August prices are consistently greater than $1.50 per pound.   Typically, a 90% to 100% increase in prices occurs during this interval which makes these activities potentially profitable for most clammers.  What remains a hindrance to going through with this type of product enhancement is the real threat that the impounded clams will be stolen.  At this time, there is only one clam farm (Swans Island) and most clammers have yet to buy into the idea of leasing clam flats either as a private or community endeavor. 

   

Attachment C:

Soft-shell Clam Enhancement
Kenneth J. La Valley, Spinney Creek Shellfish Inc.
Maine DMR Coastal Fishery Research Priority Meetings
May 4, 2000 

The most widely used enhancement method by state and municipal organizations is the reduction of fishing pressure by limiting licenses, assigning minimum size limits, and regulating catch.  However, university and professional research scientists, as well as municipal stewards have spent the better part of five decades determining enhancement methods based on the behavior and biology of the soft-shell clam. 

Soft-shell clam recruitment studies were first initiated in the 1950’s persisting through to the early 1970’s.  These studies were primarily conducted by the Maine Department of Marine Resources (Thorson, 1950; Smith, 1955; Harriman, 1963; and Stickney, 1964), and many were unpublished field notes or informal conferences.  From these early investigations it was determined that areas where water flow was disrupted would sometimes have increased settlement of soft-shell clam juveniles.  Recently a resurgence of interest on this topic has occurred.  Past studies have characteristically used furrowing, substrate augmentation or vertically placed structures to disrupt layered (laminar) flow of the incoming and receding tides (Belding, 1930; Foster, 1981; and Robinson, 1992).  Structures have included spruce branches, gravel, snow fencing, plastic mesh and lathing.  Plastic netting has been commonly used as a predator control measure during re-seeding efforts using hatchery reared seed.  During the following spring, field observations would usually find natural recruitment of juvenile Mya. 

Preliminary studies conducted by Christopher Heinig 1999 (MER Assessment Corp., Harpswell, Maine) and Spinney Creek Shellfish (1997), have documented successful enhancement using several types of vertical substrates.  The proposed advantage to vertical enhancement structures was to minimize the risk of blue mussel settlement.  However, the use of horizontally placed plastic mesh with toggles has been documented to reduce predation as well as increase settlement  (La Valley, 1997).  Dale Leavitt (Woods Hole Oceanographic Institute) has conducted multiple studies using several variations of the mesh technique.  He has observed high recruitment densities within and around the structures, and believes the added benefit of predator control reduces the impact of mussel sets (Dale Leavitt, personal communication).  In the event of a blue-mussel set nets can be removed and replaced during the course of a tide eliminating the problem and having minimal effect on enhancement efforts.  The basic design of enhancement structures can be applied to most flats, although site specific conditions require modifications that can only be determined through replicate studies. 

Recruitment enhancement techniques solely based on natural sets of soft-shell clams will likely not be successful.  In Southern Maine, and perhaps elsewhere, annual recruitment is too sporadic to sustain commercial or recreational clam resources.  Clam enhancement activities should be a combination of hatchery reared/transplanted seed and enhanced natural recruitment, in order to maximize growth before planting and overwintering survival.  By using traditional predator control measures (predator netting), productivity may be significantly increased by enhancing natural recruitment on hatchery produced seed beds.  

Enhancement Research and Development Questions
        1)  What is the impact of a clam flat on the ecology of an environment?  Are there significant environmental benefits to sustaining soft-shell clam populations?
        2)  Where are the parent stocks located?  Where do juvenile clam sets originate?
        3)  Site selection; what makes a mud-flat suitable? 

 

Literature Cited & Bibliography 

Baptist, J.P. 1955. Burrowing ability of juvenile clams.  U.S Fish Wild. Serv. Spec. Sci. Rept. Fish No. 140, p. 1-13 

Beal, B.F. 1994  Biotic and abiotic factors influencing growth and survival of wild and cultured soft-shell clams, Mya arenaria L., in eastern Maine. Ph.D. dissertation, University of Maine, Orono, Maine 499 p. 

Beal, B.F., Lithgow, C.D., Shaw, D.P., Renshaw, S., Ouellette, D. 1995  Overwintering hatchery-reared individuals of the soft-shell clams,Mya arenaria  L.,: a field test of site, clam size, and intraspecific density. Aquaculture 130: 145-158 

Belding, B.F.  1930. The soft-shelled clam fishery of Massachusetts.  Dept. of Conservation, Division of Fisheries and Game, Commonwealth of Massachusetts, Marine Fisheries Series 1, 65pp. 

Diaz-Castaneda,  Frontier, S., Arenas, V. 1993  Experimental Re-establishment of a soft bottom community: Utilization of multivariate analyses to characterize different benthic recruitment.  Estuar. Coast. Shel. Sci.  37:387-402 

Emerson, C.W., Grant, J. 1991.  The control of soft-shell clams Mya arenaria recruitment on intertidal sandflats by bed-load sediment transport. Limnol. Ocenogr. 36: 1228-1300 

Foster, W.S. 1981. An evaluation of soft clam settlement near brush bundles.  Clam Conference, Southport, ME. MA 166. No. 275. 

Heinig, C. S. and K. J. La Valley.  1999.  Recruitment Enhancement of the Soft-shell clam, Mya arenaria.  NOAA final report project No. NA76FD0096. 

Harriman, D.M/ Observations of the Effects of lime preparations on the setting and survival of juvenile clams Mya arenaria .  Department of Sea and Shore Fisheries. State House, Augusta, ME.  MA 166, No. 324. 

Hines, A.H., Posey, M.H., Haddon, P.J. 1989 Effects of adult suspension-and deposit-feeding bivalves on recruitment of estuarine infauna. Veliger 32: 109-119 

Houston, A. 1981. Brunswick clam project of 1978.  Proceedings of the Eighth Annual Clam Conference, Maine Department of Marine Resources, Boothbay Harbor, Maine, pp 136-141. 

La Valley, K. J., T.L. Howell, R.Y. Morse, B.F. Beal, and B. Dubois.  1999.
Experimental testing of field techniques for farming the soft-shell clam (Mya arenaria).
Journal of Shellfish Research. 

La Valley, K. J.  1997.  Evaluation of a mesh “tent” structure, for the enhancement of soft-shell clam, Mya arenaria, settlement.  Maine Aquaculture Innovation Center, Technical Report. 

Mann, R. 1988. Field studies of bivalve larvae and their recruitment to the benthos: A commentary.   J. Shellfish Res. 7: 7-10 

Robinson, S.M.C.  1992.  Enhancement of natural spat settlement in the soft-shell clam, Mya arenaria .  Journal of Shellfish Research.  Vol 11, No. 1 p206. 

Rodriguez, S.R., Ojeda, P.F., Inestrosa, N.C.  1993  Settlement of benthic marine invertebrates.  Mar. Ecol. Prog. Ser.  97: 193-207. 

Smith, O.R.  1955.  Experiments with Spat-catchers.  Proceedings of the Fifth Annual Conference on Clam Research, U.S.  Fish and Wildlife Clam Investigations, Boothbay Harbor, Maine, pp. 49-51 

Stickney, A.P. 1964  Salinity, temperature, and food requirements of soft-shell clam larvae in laboratory cultures.  Ecology 45: 283-291. 

Thorson, G. 1950.  Reproductive and larval ecology of marine bottom invertebrates. Biol. Rev.  25: 1-45

Woodin, S.A.  1976.  Adult-larval interaction in dense infaunal assemblages: patterns of abundance. J. Mar. Res. 34: 25-41.
   

Attachment D:

Predation and Soft-shell Clams
Brian Beal, Ph.D., University of Maine at Machias
Maine DMR Coastal Fishery Research Priority Meetings
May 17, 2000 

Predation is one of the most important biotic factors affecting clam populations along the Maine coast.  Communities that manage clam stocks should be aware of the major predators and, if possible, vary their field activities to enhance stocks (transplanting wild seed; planting hatchery-reared seed; brushing; etc.) accordingly.  Predation occurs year-round; however, most mortality by non-human predators occurs during the late summer, fall, and early winter.  March through late May are months when predation rates are typically low and, therefore, this should be the time of year when most transplanting and re-seeding activities should occur.  

The major predators of clams greater than " shell length fall into several categories:  crustaceans, worms, snails, fish, and birds. 

Crabs  
The most notorious crustacean predator in Maine is actually an “exotic” species, the green crab, Carcinus maenas.  This predator was accidentally introduced to the United States (around Long Island Sound) during the mid-1800’s.  By 1900, it was first reported in Casco Bay and by the late 1940s it had reached downeast.  Green crab population abundance appears to be related to water temperature.  The warmer the average annual water temperature, the more crabs.  Crab populations were highest during the early to mid 1950s when seawater temperatures were the warmest of the 1900s.  During the early 1960s, extremely cold winters occurred and that was correlated with decreasing crab numbers.  Today, green crab populations appear to be increasing, especially along the southern two-thirds of the coast.  Today, there are only two effective measures communities and/or individuals can use to deter crab predation:  in early spring plant seed clams that are larger than the size most green crabs can attack (1 " to 1 ") or plant smaller seed in early spring and use protective, flexible netting (usually " netting works best).  Neither of these measures are 100% effective.  There are other crab species that venture onto clam flats when the tide is high (rock crabs, Cancer irroratus -- the ones that are picked for their meat -- and small “xanthid” crabs), but these are not terribly important. 

One of the most important research topics would be to develop truly effective measures to protect clams from green crabs.  One activity could be to develop a fishery for green crabs and/or learn how to create “shedder” green crabs that would be able to compete in the market with soft blue crabs.  A fishery for green crabs could, potentially, decrease their population numbers and help increase clam numbers. 

Worms 
Although sand worms (Nereis virens)  and blood worms (Glycera dibranchiata) are predators of clams, the sizes of clams on which these organisms prey are too small to be able to do much about.  These commercially important worms can prey on clams smaller than 3 mm.  (One might see a large sand worm in a clam’s shell feeding on the clam’s tissue; however, the clam was either dead before the worm began to eat, or was weakened by something else). 

The most voracious worm predators of soft-shell clams are not closely related to sand and blood worms (Phylum Annelida, Class Polychaeta).  These predators are called milky ribbon worms (Cerebratulus lacteus) and they are in a completely different group (Phylum Nemertea, Class Anopla).  These worms are long, slender, and have no segments with feet-like parapodia (as do sand and blood worms) to move around within the mud.  This does not mean they are not mobile.   On the contrary, they are highly mobile and the only way to deal with them is to avoid them.  They can prey on clams from the very smallest sizes to the very largest by everting their long proboscis into the siphon holes of clams and eating them from the inside-out.  The smallest netting available (1/6") may help deter adult milky ribbonworms from preying on clams, but will do little to stop juveniles.  The best solution today is to place clams where this species does not exist. 

Snails
There are many intertidal gastropods, or snails, along the Maine coast but there is only one that is a soft-shell clam predator.  Moon snails (Euspira heros) are “boring gastropods” that drill a countersunk hole (usually near the oldest portion of the shell called the umbo) through the shell and evert their proboscis through this hole and consume the clam.  These snails can be found at low population densities in most coastal locations except eastern Maine (Washington County) where densities are very high especially in the mid- to upper intertidal zone.  Although much work has occurred involving the predator-prey dynamics of moon snails and clams, there is much research to be done primarily on the population dynamics of the predator.  At many locations, snails are smaller than 1 ".  Since there is a close relationship (1:1) between snail size and the size of its clam prey, in many locations clams can attain a size refuge from moon snail predation at sizes greater than 1 " in length.  Many communities in eastern Maine have planted hatchery-reared soft-shell clam seed in areas with abundant numbers of moon snails.  Although the seed have been “protected” with flexible netting, most of the clams have fallen victim to moon snail attack.  These snails can burrow beneath the nets and can forage undeterred on the seed clams.  To date, the only remedy for moon snails is the same as that described for the milky ribbon worm – plant the clams in locations with low moon snail densities. 

There is much to be gained by learning about the life history and population dynamics of these gastropod predators.  For example, we know little about the relationship between snail numbers and salinity (snails appear to have reduced numbers in areas with fresh water run-off).  In addition, we do not understand what controls population numbers of moon snails or the relationship (if any) between snail size (or age) and fecundity.  Snails at some intertidal sites appear to increase in size with decreasing tidal height, but on others, they remain small throughout the intertidal zone; why is this?  Finally, is it possible to collect enough snails and their egg collars in an area to “make a difference” in the mortality rate of clams?  To date, no community has placed a “bounty” on snails or their egg collars.  If this were done, would it make any difference in clam landings several years after the bounty were instituted? 

Fish and Birds
Fish and birds are also important predators, but, for the most part, clams can escape predation by these vertebrate organisms by reaching a size/depth refuge.  Communities that wish to guard against most benthic fish that forage intertidally can adopt one of two measures:  protective netting or planting large clams (greater than 1 " seed).  Most of the fish that venture into the intertidal zone at high tide that prey on clams are small such as the mummichog (Fundulus heteroclitus).  These fish may reach sizes of 4-6" in length and they are voracious predators of small (less than 20 mm) soft-shell clams.  Another fish that few see or pay much attention to are called wrymouth eels.  These benthic (bottom-dwelling) fish live in burrows or galleries they dig in muddy bottoms at the extreme low intertidal and into the subtidal regions.  The entrance to their burrows sometimes contains fragments of clam shells, but most that have been caught and examined closely contain small worms and bottom shrimp in their stomachs.  

Bird predation is confined mostly to black ducks (Anas rubripes) feeding during the winter months, especially January and February.  Black ducks prey on small clams that are burrowed shallowly in the mud and can nip the ends of the siphons of larger clams.  Although this latter predation does not kill the clams, it “forces” them to reposition themselves higher in the sediments where they can become more susceptible to green crab attack.  Usually clams that have had their siphons nipped will divert energy from shell growth to regenerating the siphons allowing them to reach a depth refuge from most predators. 

There have been no studies in Maine to quantify predation due specifically to fish and birds
   

Attachment E: 

Soft-shell Clam Predators
Dana E. Wallace, retired, Maine Dept. of Marine Resources
Maine DMR Coastal Fishery Research Priority Meetings
May 4 and 17, 2000 

Clams are a seafood preferred by many people.  Many predators also prefer clams to other available protein.  A list of major predators in Maine should include:  green crabs (Carcinus maenas), the milky ribbon worm (Cerebratulus lacteus), various fish such as Mummichog fundulus, birds particularly ducks, the common small shrimp (Crangon vulgaris), and Moonsnails (Espira heros).  

During the last century, the most devastating predator has been the green crab.  What follows is a brief historical account of certain efforts to deal with this menace to clams and the economy of coastal towns, and short comments about other predators.  

The Maine Department of Marine Resources (DMR, then the Department of Sea and Shore Fisheries) met the green crab problem in the late 1940s while cooperating with the towns on management efforts.  We found that green crabs were destroying clams of all sizes. 

The department worked closely with the clam investigation of the federal Bureau of Commercial Fisheries that was headquartered at the Boothbay Harbor lab from 1948 to 1962.  An early project was the harvesting of small clams from a huge bed in Western Beach in Scarborough for transplanting purposes.  The department developed a small, hand-operated dredge.  With abundant 1/4" to 3/4" clams, we planted small experimental clam farms along the coast.  Green crabs soon destroyed the beds.  It was necessary to develop some type of fence to protect planted clams or natural sets. 

During the 1950s the water temperature was rising along with a population explosion of green crabs.  Fortunately records have been kept of water temperatures at the lab since 1905 which provides good reference points.  From 1950 to `959 the annual average temperature was 49.5 F.  The clam abundance and the industry in Maine and all along the East Coast including Canada dropped to a low ebb.  Maine production was less than 100,000 bushels in 1959 and licenses dropped to 1524.  

Department effort s focused on developing effective fences.  After many years of working with the towns on various models, and spending many hours under water observing the antics of green crabs, the department developed an effective fence.  The barrier was 18" high, made of 1/2" meshhardware cloth, supported by posts and boards, with a flange on top and a 6" skirt below the fence in the sediment. 

A bill was passed in the legislature in the 1960s authorizing DMR to help the towns financially in fence building.  A few towns took advantage of this opportunity with success, but by that time the winter water temperatures had become lower with much ice and snow on the flats.  Green crabs were becoming fewer and not as much of a threat.  Towns lost interest in fences as the productivity of flats rebounded.  State production reached nearly 500,000 bushels in 1972, with 5927 commercial licenses. 

The state may face serious crab problems again.  Between 1990 and 1999 the temperature again climbed to an average of 48.5 F.  A national oceanographic scientist recently said, "Our climate is now warming at a faster rate than ever before recorded."  

The fencing law is still in force and with the successes that have been shown with protective netting on the flats, a combination of barriers may possibly protect the clams in the future.  We hope funding will be available to help the towns if the population of green crabs continues to increase as many people think is already happening.  

We should not ignore the other predators that may at any time become important factors in clam production and town management efforts.  The  milky ribbonworm, which can measure 3-4' long, is currently consuming many clams in some flats.  To my knowledge, it has been impossible to detect or control this lethal predator because of its habits.  It lives in the sediments and feeds on the clam by going down clam holes or attacking form below through the foot opening or by other means leaving only empty shells. 

In addition, various fish prey on clams.  Mummichogs have been found full of clams.  Different species of birds have been observed feeding on clams, particularly ducks.  Several types of snails, notably the moon snail, make their characteristically beveled hole in the clam shell and consume the body parts.  The common small shrimp, (Crangon,) feeds on tiny clams. 

The clam flats in any town management program should be under scrutiny at all times.  Harvesters, shellfish committee members, and enforcement personnel in a town should "know" their flats and watch carefully for predation of any kind and seek help in control methods if needed. 

A number of research initiatives are suggested: 
        1.      Reestablish the DMR program of Shore Searches for crabs of all sizes using standard procedures.  This program was carried on all along the coast from 1973 to 1985. 
        2.      Explore gametogenesis and effects of temperature on green crab survival. 

Research improved netting and fencing models to be more effective and demonstrate economic advantages and limitations. 
   

Attachment F:

Clam Resource Assessment
Chris Heinig, MER Assessment Corporation
 

Introduction 

Marine resource stock assessments in general, and soft-shell clam, Mya arenaria, assessments in specific, are extremely valuable in the management of the resources.  Stock assessment information can be used to: 1) support effort management decisions to insure sustainability of the resource, 2) establish economic value of the resource in the event of catastrophic loss and subsequent compensation, and 3) justify water and land use regulation. 

Soft-shell clam resource, (population), assessments have been carried out for many years in Maine.  A standardized assessment procedure was developed by the Maine Department of Marine Resources many years ago; the extrapolation of survey results to production volumes were originally based on the work of Belding (1930).  However, Belding’s tables were later modified by Stevens and Sampson (1981) to better reflect morphological (size and shape) characteristics of the species and conditions in Maine, thus yielding more accurate extrapolations. 

Although the survey method and extrapolation calculations have been used extensively in Maine, the method and results continue to be surrounded in controversy.  The validity and use of stock information for establishment of economic value for use in determining compensation in the event of a catastrophe, e.g. an oil spill, or justification for water and land use regulation are the least controversial, at least from the shellfish industry’s perspective.  Considerable controversy, however, surrounds the use of this information in the effort management decision process, specifically effort limitation through license issuance restriction, i.e. limited entry.  More often than not, harvesters holding valid licenses either agree with stock assessment results or argue that the assessments overestimate the stock and licenses should be reduced; those having been denied a license consistently argue that the assessments under-estimate the stock and more licenses should be issued.  Depending on the time of year assessments are carried out and the way in which the information is interpreted, either could be right.  For example, surveys conducted in the spring for use in determining license levels for the following year’s harvest season, i.e. May 2000 survey to establish licenses in 2001, will likely overestimate the resource available the following year since the legal-size clams will likely be harvested in the current year.  Assessments carried out in the late-fall, however, will minimize this error since digging pressure over the winter will usually have a negligible effect on the stocks, particularly in years of heavy ice cover or low demand/price. 

Regardless of the time of year when surveys are carried out, the failure to account for growth and consequent movement of just-sub-legal clams into the legal-size range during the following year will inevitably lead to underestimation of the stock.  At least one projection model has been developed to predict “following-year” stock status based on current year survey data.  As in any model, certain assumptions need to be made, specifically growth rate and mortality.  Growth rate, both incremental and annual, is obviously subject to environmental conditions, particularly temperature and food availability, and is therefore regionally-, if not site-specific, e.g. Casco Bay vs. Machiasport.  Therefore, a model developed for Casco Bay will be unlikely to be applicable or suitable further east along the coast.  Mortality has multiple components, including direct harvest mortality or “take”, harvest-associated mortality, e.g. suffocation due to burial or exposure, predation, and natural attrition.  These are very difficult to ascertain accurately and, as with growth, will vary considerably from one location to another.  Nevertheless, despite the complexities, such projections may be essential if proper management is to be achieved in the future. 

Clearly, in order to be effective, stock assessments must be accurate and the results believable and accepted, indeed, under certain circumstances, irrefutable.  The central question is:  Should this goal be pursued?  If yes, then:  How can this goal be achieved, and what research is needed to achieve it? 

References

Belding, David L., 1930.  The soft-shell clam fishery of Massachusetts, Commonwealth of Massachusetts, Dept. of Conservation, Div. of Fish and Game, Mar. Fish. Sec., No. 1, Boston, Mass., 65pp. 

Stevenson, D.K and D.B. Sampson, 1981.  A method for improving mean density estimates obtained from intertidal clam census surveys, Maine Dept. of Marine Resources, W. Boothbay Harbor, Maine, presented at the 1981 Boothbay Harbor Clam Conference, May 7-8, 1981. 

Questions:
1.   Are assessments worthwhile?
2.   What are the constraints on conducting clam surveys?
3.   If cost is a concern, is employment of shellfish harvesters in the assessment process appropriate? 
4.   Will assessments conducted by harvesters be considered acceptable in court in cases of litigation?
5.   What other means can be used to reduce costs? 
6.   Are alternative sources of funding available or should/can these be developed?
7.   Is investigation into a simpler methodology warranted or supported? 
8.   If so, is any possible loss of accuracy acceptable?
9.   How can worthiness be clearly established and conveyed to the industry/resource managers?
10. Do alternative sources of information exist that could be used to determine stock status? 
11. If so, how accurate is the information and what quality qualifiers are needed?
12. Does the assessment methodology need further validation and/or modification?  If so, in what ways?
13. Should other observations, i.e. predators (green crabs), be specifically included as part of the standardized survey? 

Suggested research areas: 
1.   Validation of survey methodology through post-survey harvest count and comparison to survey estimates - immediately after survey.
2.   Validation of projection model through post-survey harvest count and comparison to survey estimates - year(s) following survey.
3.   Development of an alternative, simpler yet adequately accurate methodology.
4.   Development of regional estimates for growth rate (incremental/annual) and the various components of mortality.

 

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