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
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 ¼"
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 ½" to 1 ¾") or plant smaller seed in early spring and use
protective, flexible netting (usually ¼" 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 ¼".
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 ¼" 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 ¼" 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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