The sea scallop (Placopecten
magellanicus) had a landed value of $4.4 million in Maine in
1999. The same year there were 741
boats with commercial scallop licenses and 353 scallop divers in Maine.
The state also licenses non-commercial draggers, and allows unlicensed,
limited, non-commercial diving.
Scallops are managed by both
the federal and state management agencies.
The federal scallop plan, which is developed by the New England Fishery
Management Council and administered by National Marine Fisheries Service (NMFS),
is predominantly an offshore plan that is focused on the large scallop resource
and fishery on Georges Bank. With
minor exception, Maine boats no longer participate in the federal scallop
fishery. Maine is unusual in New England because it has a viable inshore,
small-boat scallop fishery, a significant portion of which occurs in state
waters. Of the 741 scallop license
holders, only 32 vessels hold general scallop permits that allow them to harvest
400 pounds of scallops per trip outside state waters.
At most a couple of Maine scallopers hold limited access federal permits.
The Maine scallop fishery is
pursued by a variety of fishermen: lobstermen
fishing during the off-season, draggers who also fish for ocean quahogs and sea
urchins, and divers who also dive for urchins.
Some groundfish draggers will rig for scallops if the abundance is great
Maine has retained the right
to manage sea scallops within its state waters, despite the federal management.
State management has been limited to season, gear, and scallop size
restrictions. Scallops are a
secondary fishery for most Maine fishermen, and the fishery has been managed
principally to minimize gear conflict with the lobster industry.
For this reason, the season runs from December 1 to April 15.
Many management decisions continue to be made by the state legislature.
The Department of Marine Resources (DMR) has conducted limited scientific
research and biological monitoring of the scallop fishery; however, a position
has recently been assigned to focus on scallops and other fisheries in eastern
Interest in scallop
enhancement is the latest development in the fishery and is providing the
impetus for far more research and experimentation.
Information about scallop enhancement techniques came as the result of a
trip to Japan in May, 1998 organized by DMR and the Maine Aquaculture Innovation
Center. Fishermen along the coast
are now experimenting with setting spat bags to collect spat for redistribution
on scallop beds. There is interest
in using the same technique for grow-out in private aquaculture.
DMR Research Priorities Project
This scallop 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
The project was conducted
under contract by the Gulf of Maine Aquarium (GMA).
It was funded by a planning grant from the Economic Development
Administration, the DMR, and the University of Maine Sea Grant Program.
The GMA consultants, DMR, and the University of Maine Marine Extension
Team staffed the project.
For each fishery, at least
one, all-day meeting was held. The
meetings were designed to be non-regulatory, neutral, and inclusive following a
format developed by the GMA in previous efforts for other species. The meetings
brought together fishermen, academic scientists, government scientists, and
fishery managers as equals. They
created an open environment for
curiosity and questioning. Seven
meetings were held on five fisheries to achieve broad input along the coast.
Four topics were chosen for
each species and scientists were invited to make short presentations on each of
the topics. In addition each of the
presenters were asked to write a short analysis on some aspect of the topic or
his/her research questions for the final report.
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. Each of the four sessions had the same format.
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 his or
her major research questions about the species.
After that, the group discussed the topic and the presentation,
generating a list of questions that were summarized by one of the facilitators
for later ranking. At the end of
the day, one half hour was spent in an informal ranking process where everyone
was given 10 sticky notes to stick by the topics of their choice.
The day wrapped up with an oral evaluation and discussion of follow-up
and ways to improve the process.
Publicity for the meetings was
customized for each fishery. Methods
included direct mail to license holders, personal contact with association
leaders, and posters distributed to sites in each town.
All of the meetings were covered in press releases to local and statewide
Scallop Research Priority Meeting
The scallop meeting was held May 16,
2000 at the University of Maine at Machias from 9 a.m. to 5 p.m. Topics and presenters included:
Assessment and Dan Schick, Maine Dept. of Marine Resources
2. Biology/Oceanography Brian Bea,
Ph.D., University of Maine at Machias
Enhancement Richard Taylor, Gloucester, MA
Higgins, Darling Marine Center
Forty-one people attended the
scallop meeting. Attendees included
scallop draggers and divers, people involved in scallop enhancement,
aquaculturists, DMR managers and biologists, a member of the Maine State
Legislature, several consultants, a representative of The Nature Conservancy,
and researchers from the University of Maine and the University of Maine at
Results of the meeting are
presented in two different formats:
1. Priorities voted by the group (Section VI) which are presented with
2. A detailed, categorized listing of questions, observations, and opinions
articulated during the discussion (Section VII).
The dual format is necessary
in order to capture the richness of the meeting.
The priorities organize thought and focus effort.
The details are essential because it is the local observations and
questions that provide the raw material of good scientific hypothesis.
Although the scallop meeting was divided into four segments: Assessment and Current Management, Biology/Oceanography,
Enhancement, and Gear, the report is not structured around those categories
except where it makes sense. Many
topics, such as growth and reproduction, and oceanography were raised in several
of the segments. Therefore we have
given precedence to the priorities articulated at the meeting rather than those
used to organize the meeting. Furthermore,
we have not attempted to categorize the research questions by scientific
discipline. Under a given priority
one might find questions for oceanographers, basic biologists, and economists or
anthropologists. The solutions to
these problems require collaboration between disciplines and between science and
industry. The first step is to
articulate the questions in such a way that 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.
Research Context and Group Research Priorities
The issues discussed at the
scallop meeting were confined entirely to inshore Maine scallop issues and did
not cover questions about the offshore Gulf of Maine or Georges Bank fishery.
Scallops have been a cyclical species in inshore Maine, occurring in
patches that tend to be fished out quickly.
Research questions focus on techniques to understand the mechanisms that
control abundance of scallops, thereby providing insight for actions to harvest
within the constraints of the species.
Because the Maine scallop
fishery has been managed largely to avoid gear conflict with the lobster
fishery, rather than for biological purposes, it exists in an unusual vacuum.
On the scientific side, unlike urchins, scallops do not have a research
fund and there has been little or no research done on Maine scallops in the
recent past. There is no one in DMR or the University whose primary
interest is scallops, although DMR is in the process of committing staff to
scallops. Fishermen involved in
spat collection for enhancement are having difficulty finding scientific
advisors with capacity to help them. On
the management side, fishermen and managers have little history of interaction
on resource, as opposed to gear or gear conflict, issues.
This provides an opportunity for collaboration with a relatively clean
The Governor's Marine
Fellowship program was suggested as one way to address the shortage of principal
investigators focused on scallops. It
was suggested that fishermen be included in the mailings about the availability
of fellowships, so that the fishermen, as potential one-third funders of a
fellowship, could initiate ideas, seek out researchers with students, and
stimulate local scientific interest in scallop questions.
In the traditional fishery,
interest in rotational management, spawning refuges, and other measures to
reduce the boom and bust features of the fishery increasingly call for
scientific guidance that is non-existent at this point.
Scallop Priority 1:
with clams and urchins, using enhancement as a lens focuses scallop research
questions on understanding nearshore oceanography and scallop life history at a
most basic and local level. If spat
is to be collected, the very nearshore currents need to be understood, as does
the transport of spat. The desire
to collect scallop, as opposed to starfish or any other spat, focuses questions
on scallop spawning behavior, triggers, and location of broodstock.
Research priorities are:
Fine scale research and current modeling to determine scallop larval
Where is the effective broodstock for each scallop area?
What are the mechanisms that determine the relationship between adult
scallop biomass and recruitment success?
Do adult scallops or scallop larvae move inshore and/or offshore?
Scallop Priority 2:
Life history, growth, and behavior questions also rise to
the top. What is the growth rate in
scallops in different parts of Maine? What
are the significant determinants of growth?
The role of predators also emerges as important because of both the spat
collection and the distribution of seed later.
What triggers scallop spawning? Is
it density dependent?
Document and understand scallop growth rates in different areas.
Study predation on scallops at larval and juvenile life stages.
Scallop Observations and Questions from Discussion
help the wild fishery by maintaining a large broodstock to provide eggs to it?
Are there any
natural markers for scallop populations that are heritable that could provide
a mechanism for tracking populations?
Assessment and Surveys
Do scallops have
natural cycles? If so, what
Can we include
younger year classes in assessments?
What is a
realistic purpose for a scallop assessment?
Projection of yield from scallops that are already on the bottom? Projection of future population levels?
Best means of
getting a good scallop assessment would be to have a fishery- independent
survey that samples all areas, not just the heavily fished areas.
collection as an index for assessment.
assessment be regional or local?
Do a Cobscook Bay
Develop an annual
pre-season industry or DMR survey to determine scallop size classes on various
grounds and decide whether to open based on the survey results. This could be done statewide or in specific areas such as
Need a calculation
of catch at age from shucked fishery.
How do you
calculate fishing mortality rate in a rotational fishery?
What is the
relationship between scallop spawning and starfish spawning?
What is the
relationship between good scallop and starfish sets?
Do urchins and
scallops compete at any life stages?
When I find a
scallop bed covered with barnacles, the meats are larger.
Why is Cobscook
Bay such a good place for scallops?
and Machias Bays. Why are they so
different? Is it because of the
size of the lobster fishery?
How do we
repopulate areas that were once productive scallop beds?
Do an accurate
assessment of what is in an area prior to enhancement.
Use a flow cam as
they do in Prince Edward Island to understand the spawning dynamics and advise
fishermen when the spat are in the water.
out-perform gillnet for spat collection?
strategies would avoid predation? Should
we collect spat earlier?
What are the best
places to collect spat: general
characteristics and specific locations?
Mike Dadswell in
Canada has found good spat collection in circular gyre over a mud hole where
larvae won't settle.
What are the best
places to put spat for grow out?
control be done prior to reseeding?
Develop a protocol
to measure success of enhancement across the state.
Can we identify standardized measures that can be used in different
protocol for collection and evaluation for enhancement statewide.
Can we identify
indicators for spawning in order to establish efficient spat collection
Be careful not to
spread disease through spat transfer.
specific gonadal index so that people know when to put out spat collectors.
index monitoring program.
Develop a tag for
the spat so we know whether enhancement is working.
Canadian 10-year spat collection time series.
Can we limit the
impact of dragging on small scallops?
getting out of the drags?
Set up the rings
so they do cull and allow fishermen to close up spaces between rings.
Hang rings staggered?
If 3 1/2"
rings don't work, then research other ring sizes and configurations.
What about cookies, liners?
Solve the discard
problem. Scallops that freeze on
deck are dead when they are discarded.
Can we minimize
the environmental impact of dragging?
Does a rigid drag
cause less damage?
When we changed
drag width, we made impact worse by not addressing the weight of drags.
Collate past work
on drag impacts to identify what work needs to be done.
Define better what
a functional benthic (bottom) community is.
After, Control, Impact) studies assess impact by measuring change. Look at the variability of the system in the control and test
sites and then measure impact on the test site.
Too complex to
study gear impacts on the bottom given there are no untouched areas. Many
variables in how dragging is done.
Need gear impact
done by credible scientists.
design and restrictions with what we know about the size of scallop necessary
to protect as broodstock.
cumulative impacts of dragging in Cobscook Bay on the scallop population, the
habitat, and the water column. What
is the impact of the sediment plumes from dragging?
role of predation through the scallop life cycle.
triggers spawning in male and female. What
role does density of scallops play in setting off synchronous spawning?
What are the
relative contributions to spawning of scallops at different sizes/ages?
Do we know what size we need to protect to preserve broodstock?
What is the
relationship between parents and juveniles?
What is the source of juveniles that settle in a given location?
factors that contribute to the very high natural mortality in scallop larvae.
Canadian work on
spat collection shows high levels of spat in areas they won't settle.
variation in growth rates of larvae and adults statewide.
Are there multiple
sources of spat that supply good growth areas?
Is there any
relationship between the length of the cilia and the ability to feed the way
there is in urchins?
color in scallops?
Why are scallops
in Calais either tiny or dead?
How do we keep the
scallop resource sustainable without privatization or ITQs?
tools for their success: gear
Do input controls
include limits on crew size. Those
limits are significant factor.
Are there benefits
to spawning refuges or rotational management?
To maximize egg
production, should large scallops be protected the way large lobsters are?
regulatory options for issues such as movement of seed and protection of
Need to learn from
other enhancement efforts worldwide: Canada,
Japan and New Zealand.
What can be
learned from the Passamaquoddy Bay scallop management approach?
Migration and Behavior
Is there a
relationship between foggy weather in the summer and peaks in scallop
abundance historically? If so, is
it related to spawning or growth?
What are the
migratory patterns of offshore scallops?
Do they move inshore? Do
they repopulate the bays?
Is there migration
of inshore scallops offshore?
Do scallop larvae
from different regions behave differently?
oceanographic characteristics that relate to scallop larval transport.
may be best when sea surface temperature is between 8-9°
transport questions in Cobscook Bay are important to pursuing enhancement but
they need to be done at a finer scale than has been done -- ground-truthed and
made real time.
circulation model uses different system for data management and may be useful
in improving the resolution of the models.
Need synthesis of
what is already known in layman's language for use in planning and doing
collaborative scallop enhancement efforts.
What are the
market implications of various size restrictions such as increases in minimum
size or the imposition of a large measure.
Concern that spat
collection will lead to aquaculture rather than enhancement of the traditional
Once we develop
enhancement techniques, who will own those scallops?
Will these be regional efforts? Implications
for whole fishery?
Will DMR draw the
line between fishermen doing enhancement and aquaculturists doing this for
What will the
governance structure be for enhancement efforts?
social questions from the beginning as an integral part of all the science
research necessary to make enhancement work.
Don't rush to
decide policy issues before we have worked out what really works and is cost
effective for enhancement.
What will be the
issues between scallop enhancement efforts and other fisheries?
studies to understand inshore/offshore migration and stock structure along the
coast. Are there differences
May 16, 2000 at
University of Maine at Machias
GSH1 Sunset, 04683
Rep. Martha Bagley Machias
Sandra Wallace Pembroke
James Wallace Pembroke
Carlo Doria Portland
Cecil Cates 138 Water St., Eastport 04631
Jesse Leach Rt. 15 Box 1220, Penobscot 04476
Ralph DeWitt 9 High St., Eastport 04631
Hank Stence Lubec
Lanny Wood HCR 70, Box 36, Machiasport
Bruce McInnis 1 High St., Eastport 04631
Austin Humphrey P.O. Box 94, Perry 04667
RFD Box 1455, Stonington 04681
RFD Box 1455, Stonington 04681
Brian Beal University of Maine, Machias 255-1314
Jane Harrison HC 70 Box 28, Machias 04654
37 Hillside Rd, Orono 04473
Box 153, Searsmont 04973
P.O. Box 27, Perry 04667
John Higgins UM Darling Marine Center, Walpole 04573
Dennis Fraughton 2161 Friendship Rd, Waldoboro 04572
Box 7002, Gloucester, MA
Kenny Daye 27 School St, Lubec 04652
Bill Daye 27 School St. Lubec 04652
Sean Daye 27 School St. Lubec 04652
Will Hopkins 4 Favor St., Eastport 04631
Anne Hayden 6 Bowler St., Brunswick 04011
Jim Dow P.O. 974, Blue Hill 04614
Dana Morse Sea Grant / UM Cooperative Extension 563-3146
Linda Mercer DMR, Boothbay Harbor
Laura Taylor DMR, Augusta
Penn Estabrook DMR. Augusta
Sue Inches DMR. Augusta
Dan Schick DMR, Boothbay Harbor
Paul Anderson Sea Grant / UM Cooperative Extension
Chris Bartlett Sea Grant /UM Cooperative Extension
Don Perkins Gulf of Maine Aquarium
Box 7549, Portland 04112 871-7804
Robin Alden PO Box 274, Stonington 04681
Very Brief History of Scallop
Richard Taylor, Scalloper,
Maine DMR Coastal Fishery
Research Priority Meetings
Spat collection from the wild and reseeding:
Japan, New Zealand, Magdalen Islands, Canada
Hatchery based seed production for contained culture:
China, Chile, France
Choices: What do you want
the scallop fishery of the future to look like?
Status quo - meaning continue the way the fishery is now:
Develop area management, where scallops are allowed to grow to a large
size to increase the value of each scallop.
With the success of the 1999 Maine inshore spat collection, you can see
the size of these animals at the end of the year, about the time the scallop
Begin small scale spat collection to start getting a better sense of
the potential of reseeding small scallops.
The initial effort last fall was quite productive.
One advantage of the spat collection/reseeding method is that scallop
can be put out in areas where they don't show up very often but where we know
from occasional sets in the past that they will thrive.
Reseeding a single year class allows letting scallops grow before going
through them with the gear.
Develop intermediate culture areas where scallops within spat
collectors can be left to grow to a size suitable for reseeding.
Develop contained scallop culture (cages, lantern or pocket nets).
This option offers the benefit of maintaining a larger spawning biomass
to increase larval supply to the fishery and for spat collection.
A combination of most or all of the above.
Yield or landings as a function of the number of participants:
An increase in the scallop population will
result in increased landings and increased total earnings, however as long as
the numbers of boats are allowed to increase unchecked earnings for each boat
will stay about the same. There
are at least two approaches to this situation.
One method is to limit the number of licenses,
that is, limit the number of slices of the pie, and with this comes a
particular set of other problems involving who gets to participate.
Another solution is to greatly increase the
number of scallops by using methods that increase the survival of scallops
during the first year, or 'grow the pie bigger'.
The Japanese system had a stated objective in 1970 of increasing
economic development in fishing communities.
Their methods have allowed increased participation by a larger number
of fishermen and increased employment in the processing sector.
Topics for further research and consideration:
local areas have been important to the fishery over time.
Where does scallop seed show up over and over? Where does scallop seed occur only sometimes, but where they
grow well? We know that scallop
larvae are carried by the currents for about 40 days and we can see that
certain areas seem to retain the larvae repeatedly.
The role of bottom type or substrate is a key factor here:
generally we know that gravelly areas seem to have a lot of scallops.
We know that the role of predators such as starfish and crabs is
important as well.
Although it would be great to get the best scientific level information
about these areas, we don't have to completely understand and document the
'why' of it to treat these areas as special.
Every fisherman who has been a part of the industry knows pretty much
where they are. The harder
question is how these areas should be managed to maximize what they already
provide. The success of the area
closures on Georges is one way to go, but is much easier to enforce when the
areas are a hundred miles offshore and each scallop vessel has a
satellite-tracking device. It's a
harder problem to solve inshore and really goes to the issue of how we think
about what we are doing. An old skipper of mine said way back,
'Do you think human nature is going to change?'
Probably not, but if you see there is more product and more money to be
made by doing something a little different, that change will come.
basic information will help us to make better choices looking ahead.
Perhaps the most important is figuring out when and where spawning
occurs. Generally we figure it is
in the fall but this is one aspect that needs to be documented if spat
collection is to be reliably integrated into any future plan.
These papers have provided insight into the
many parts of the solution:
M.F. (1994) Enhancement and Management of New Zealand’s 'Southern Scallop'
Fishery, In Proceedings of the 9th
International Pectinid Workshop, Nanaimmo, BC, Canada, April 22-27, 1993,
Bourne, N.F., B.L. Bunting, and L.D.Townsend (eds), Vol. 2, pp131-136.
Cliché, G. and M. Giguere (1998) Final report
of the research program on scallop culture and restocking (REPERE), 1990-1997,
Canadian Industry Report of Fisheries and Aquatic Sciences 247, 74 p.
R.L. (1971) Periodicity of sea scallops abundance fluctuations in the Northern
Gulf of Maine, Maine Dept. Sea and Shore Fish. Res. Bull. 31.
Gallager, S.M., J.L. Manuel, D.A. Manning, R.
O'Dor (1996) Ontogenetic changes in the vertical distribution of giant scallop
larvae, Placopecten magellanicus, in
9-m deep mesocosms as a function of light, food, and temperature
stratification, Marine Biology 124:679-692.
B.G., R.E. Scheibling, M.A. Barbeau, A.W. Hennigar, L.W. Taylor, A.J. Windust
(1996) Dispersion and mortality of a population of sea scallop (Placopecten
magellanicus) seeded in a tidal channel, Canadian. Journal of Fisheries
and Aquatic Sciences, 53:38-54.
H. (1990) Some aspects of offshore spat collection of Japanese scallop, in
Marine Farming and Enhancement, Proceedings of the 15th US-Japan Meeting on
Aquaculture, A.K.Sparks (ed), NOAA Tech. Report NMFS 85, 85:35-48.
H. (1991) Successful HOTAC methods for developing scallop sowing culture in
the Nemuro District of East Hokkaido, Northern Japan, in
Marine Ranching, Proceedings of the 17th US-Japan Conference on
Aquaculture, R.S. Svrjcek (ed.), NOAA Tech. Report NMFS 102, 102:107-116.
H. (1992) Breeding season of Japanese scallop off the eastern coast of
Hokkaido, Marine Ranching, in
Proceedings of the 18th US-Japan Conference on Aquaculture, R.S. Svrjcek (ed),
NOAA Tech. Report NMFS 106, 106:77-83.
Ito, S. and A. Bykuno (1990) A history of scallop culture in Japan, in
Proceedings of the Australasian Scallop Workshop 1988, M.C.L. Dredge, W.F.
Zacharin, and L.M. Joll (eds.), Tasmanian Government Printer, Hobart,
Australia, pp. 166-181.
D.R. and M.A. Sewell (1998) Fertilization success in free-spawning marine
invertebrates: review of the evidence and fisheries implications, in
Proceedings of the North Pacific Symposium Invertebrate Stock Assessment and
Management, G.S. Jamieson and A. Campbell (Des), Canadian Special Publication
of Fisheries and Aquatic Science 125, pp.159-164.
M. J. (1989) The feasibility of enhancing red sea urchin, Strongylocentrotus
franciscanus, stocks in California, Marine Fisheries Review, Scientific
Publ. Office NMFS, Seattle, Wash., 51(2): 1-22.
J. (1990) Administrative, legal and sociological difficulties of scallop
culture enhancement. Proceedings Australasian Scallop Workshop, M.C.L. Dredge,
W.F. Zaccharin, and L.M. Joll, (eds.), Tasmanian Government Printer, Hobart,
Australia, pp. 264 -271.
S.R., L.W. Botsford, J.F. Quinn (1998) The impact of coastal circulation on
the spatial distribution of invertebrate recruitment, with implications for
Proceedings of the North Pacific Symposium Invertebrate Stock Assessment
and Management, G.S. Jamieson and A. Campbell (Des), Canadian Special
Publication of Fisheries and Aquatic Science 125, pp. 285-294.
Scallop Assessment and
Daniel Schick, Maine
Department of Marine Resources
Maine DMR Coastal Fishery
Research Priority Meetings
The population biology of a stock can be
described in a few simple terms. First,
there are three factors that can make the population grow, or make the biomass
larger. The first is recruitment:
the addition of animals to the stock through reproduction.
The second is growth of individuals.
The third is immigration of animals into the area defined as being the
location of the stock. There are
three factors that can make the population decrease, or make the biomass
smaller. The first is natural mortality, which includes death due to
old age, disease, or predation. The
second is emigration: the moving
of animals out of the area defined as being the location of the stock.
The third is fishing mortality, or death caused by fishing activity of
man. This can be divided
into individuals caught and kept, caught and discarded but died anyway, and
individuals killed by the fishing activity but not caught.
In managing a stock, there is usually only one
of the above factors that can be manipulated to influence the size of the
biomass of the stock and that is fishing mortality.
In the case of the sea scallop, it may be possible to manipulate the
recruitment of individuals into the stock as well as fishing mortality.
Assessment of the status of a stock can be done
by several methods. The method
used depends on the data available and the length of time that data has been
gathered. Some indices of
abundance can be obtained from the landings record, especially if the landings
can be broken down by area fished. If
there is any effort information collected in the fishery, i.e. number of hours
fishing, the catch per unit of effort can provide another index of abundance.
If there is any biological data collected from the fishery, i.e. size
frequency of scallops caught, then a catch at age matrix can be developed and
more sophisticated population models can be used.
Finally, if there is a fishery independent survey of the population
from which a separate catch per unit effort (CPUE) index and catch at age
matrix can be produced each year, then the data lends itself to the best
Most of these data elements are available for
the offshore scallop population and that population has been modeled using the
Collie-Sissenwine modification of the DeLury model for USA stocks.
This model estimates biomass and total mortality and is based on survey
indices of abundance and fishery removals at size, or assumed age.
The catch at size is not always well represented, which increases the
error in the model results. Canadian
assessments give indices of abundance on the basis of survey data, logbooks
and port sampling data and in periodic assessments they use cohort analysis,
or separable virtual population analysis to generate estimated numbers at age,
biomass at age and fishing mortality (F) at age.
From this data they use a yield per recruit analysis to develop Fmax
(fishing mortality rate that will give maximum yield/recruit) and F0.1
(fishing mortality rate where the slope of increasing yield with increasing F
is a tenth of the initial slope) and then develop catch projections using
these F’s, other selected F values and assumed average recruitment to
predict biomass over the next year and therefore what the TAC should be under
various fishing scenarios. In
some assessments, the Canadians use a Leslie depletion estimator to generate
an exploitation rate from catch, effort and survey data.
The F from the exploitation rate is compared to Fmax and F0.1
values to assess whether the fishery is taking too much.
The State of Maine collects scallop landings
information, but collects no effort data, nor does it do any fisheries
independent survey work. Thus the
State has little information with which to determine the status of the stock
of scallops along the coast. The
National Marine Fisheries Service does not do a scallop survey in the Gulf of
Maine. As a result, almost
nothing is known about the stock. No
assessment of the status of the scallop stock along the Maine coast has ever
There are two general types of controls imposed
on fisheries to limit fishing mortality.
They are input controls, related to limiting effort, and output
controls, related to limiting catch directly through some form of quota. Input controls can be limits on season length, days at sea,
boat size, numbers of vessels, gear restrictions, etc. Output controls can be limits on catch per trip, individual
quotas, or overall annual or seasonal quota.
In the current Maine scallop fishery,
management is based on input controls, i.e., season length and gear size
(dredge width) restrictions. Traditionally
there has been a 3" shell height minimum and more recently a graduated
3" to 3-1/4" to 3-1/2" ring size increase.
The ring size limits are the first regulations that deal with the
biology of the scallop. The
season timing and duration is simply a measure for reducing gear conflict with
fixed gear fisheries, rather than anything to do with the capacity of the
scallop population to support the fishery.
The drag width limits have more to do with competition between
different vessel size classes and their associated socio-economic differences
than condition of the stock. The
minimum shell size was purportedly directed at the minimum spawning size of
the scallop, but was unenforceable, as the unshucked scallops were a mix of
the legal and too small scallops on the sorting table and the relationship
between shucked meat size and shell size was not a good one.
The ring size minimum of 3-1/2" starts to
address the need for considering the rapid growth rate and rapid increase in
meat yield as scallops increase in size.
Once a scallop reaches 3", its meat yield will almost double each
year it is allowed to grow for at least the next three years. Allowing scallops to increase their meat yield prior to
capture increases their yield per recruit.
It may well be that the best yield per recruit, and therefore the best
yield from the resource can be gained by using 4", or perhaps larger
In order to build a management plan for
scallops in coastal Maine, we need to establish some goals in terms of what we
want from this fishery. Do we
want greater yield per recruit? Do
larger meats command a better price in the market?
Do we want a consistent annual harvest rather than the boom and bust
fishery evident from the landings record?
Will protecting a portion of the spawning stock biomass provide us with
a constant supply of recruits?
We might gain some insight by looking at the
offshore scallop fishery along the East Coast.
For years the fishery was severely overcapitalized with too many large
vessels that had a combined capacity easily capable of fishing down each
successful year class very quickly. This
created a fishing mortality rate that was much too high and the boom or bust
landings typical for that scenario. A few years ago, large areas of Georges Bank scallop grounds
were closed to scalloping due to depletion of the groundfish resources there.
The scallops in these areas increased in size each year and new
recruits settled into these areas and grew in good concentration.
After three years, there was a huge biomass of scallops there.
Some of these areas have been opened to scalloping on a limited basis
and two areas off the mid-Atlantic were closed due to the heavy concentration
of small scallops there.
A system is evolving in the offshore fishery
that is based on rotating open and closed areas to maximize yield per recruit
by protecting juvenile scallops until they reach optimal market size.
A system such as this might work very well along the Maine coast,
especially if the recruitment to the resource is enhanced by the capture and
growout of scallop spat for release at a size that is beyond the high natural
mortality size range. If the scallop population biomass grows, especially at
the hands of fishers engaged in enhancement of the stock, the issue of how
many more fishers to let in to the fishery will have to be addressed.
In order to choose what form of management is
appropriate for Maine scallops, there are two huge questions to be answered.
First, what is the relationship between spawning stock biomass in Maine
scallop beds and recruitment success in those beds?
What percentage of scallop larvae that settle in Maine scallop beds
come from Maine scallops? If a
reasonable percentage of Maine scallops are a product of Maine scallop
spawning, then there is a good reason to manage the scallop stock to protect
the spawning stock at some appropriate level.
If there is no parent progeny relationship, then there is no need to
maintain a spawning stock biomass and the best management would be to maximize
yield per recruit.
The second question is what is the relative
value of refugia and larger ring size in terms of recruitment success in the
population? In a refuge, all
scallops are protected and with a large ring size, scallops are allowed to
spawn before recruiting to the fishing gear.
In a refuge, large scallops would exist in close proximity presumably
to maximize their spawning synchrony and therefore spawning success.
With large ring size, all scallops would spawn before being caught,
providing a much wider distribution of scallop spawning.