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by Natalie Springuel
Maine's inshore scallop catch has been declining steadily over the past few years, raising concerns among fishermen who have long-depended on the seasonal fishery for income during the winter months. At the same time, scallop stock enhancement projects have been cropping up from Canada to Cape Cod and further south. Information about these efforts has found a ready audience among fishermen and researchers concerned for the future of the scallop resource.
Most often, these scallop projects involve collecting larvae as they float in the water column in search of a place to settle and grow. The goal of collecting larvae, or spat, is to protect scallops at the most vulnerable time in their life cycles. The spat can be nurtured and then used to reseed depleted beds, or it can be held and grown out to market size.
This article, the first of a two-part series, will cover the nuts and bolts of scallop spat collection and the science driving these efforts in Maine. In the next issue of CFN, The Science Side will examine what happens to the spat when it is big enough to reseed depleted scallop beds and how these efforts might contribute to a sustainable scallop fishery.
So far, spat collection on the coast of Maine has been a collaborative effort involving a diversity of people and organizations. To name just a few, the Maine and New Hampshire Sea Grant Programs have provided technical expertise and funding. Dozens of fishermen throughout the coast have deployed and monitored spat bags and offered their knowledge of scallop beds.
Nonprofit involvement includes the Cobscook Bay Resource Center (CBRC), a community-based organization in Eastport working on resource management and sustainable economic development in the Cobscook Bay region, the Northwest Atlantic Marine Alliance (NAMA), a community-based organization seeking to restore and enhance an enduring Northwest Atlantic marine system, the Stonington Fisheries Alliance (SFA), also a community-based organization promoting responsible local fisheries management; and the Beals Island Regional Shellfish Hatchery (BIRSH), which works to enhance Maine's shellfish resources through aquaculture, applied research, technology transfer, and public education.
Maine's Department of Marine Resources, the agency responsible for overall management of scallops in the state, has issued permits for spat collection and offered valuable biological expertise.
Scallop spat are collected using mesh bags filled with Netron, a polyethylene material to increase surface area. Six to 10 bags are deployed on an anchored line, which has a toggle buoy above the topmost bag, to keep the line upright, and some sort of buoy at the surface. Many fishermen have used their lobster buoys.
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Fertilization
The sea scallop (Placopecten magellanicus) is a cold-water species that can live from shallow subtidal areas to deep water.
In coastal Maine, sexually mature sea scallops release sperm and eggs into the water column, where fertilization takes place, sometime around late July. The factors influencing the process are not well-understood, though.
CBRC's Will Hopkins characterized the chanciness of fertilization by saying, "By the grace of God and currents, you have spawn."
A biological limitation of this shellfish species in the wild is that reproduction is often triggered by other scallops spawning in the same area. Therefore, fewer scallops on a bed means less chance for egg fertilization, one of the possible problems causing overall scallop population decline.
When fertilization does occur, the larvae or spat that are produced float throughout the water column for approximately 40 days. Then they find a hard surface on which to settle, attaching themselves to the surface with byssal threads.
During this settlement period of two to three months, larvae are tremendously susceptible to changes in environmental conditions and predation. Chances of survival in the natural environment are slim.
According to Erin Fisher, a marine biologist who is currently an Island Institute Fellow working on scallop stock enhancement in Stonington, "A scallop larva probably has a one in a million chance of surviving to adulthood.'
Spat collecting efforts are intended to increase the survival rates of the larvae and thereby ensure stock for future reseeding.
Looking for options
In 1999, fishermen, scientists, and fisheries managers from Maine looked to an unlikely source for answers on how to ensure the scallop fishery's longevity. They flew to Japan. There, they found the solution could lie in creatively combining successes in the aquaculture industry with more traditional wild capture techniques.
Closer to home, they also learned some lessons from researchers and fishermen in the Canadian Maritimes, who have been involved in scallop stock enhancement projects for nearly a decade.
The scallop resource in the Northwest Atlantic has depended on scallops settling naturally onto the sea bottom a few weeks after spawning. Instead of passively taking their chances with nature, the Japanese believe that collecting and taking care of spat is fundamental to a sustainable fishery. They devised a technique to collect scallop larvae as it floats through the water column.
Variations on this technique are being explored in the Stonington area, Cobscook Bay, and Saco Bay, Maine, where researchers and fisherman are learning more about localized scallop patterns.
Stonington, ME
"Stonington is just a hotbed of sea scallop activity!" said Dana Morse, Maine Sea Grant extension agent.
Indeed, it was in the Stonington area that Marsden Brewer, coordinator of the Wild Scallop Stock Enhancement Project, and about 30 fishermen first set out to capture scallop spat. In the fall of 1999, the first series of spat bags were deployed throughout eastern Penobscot Bay, Jericho Bay, and Blue Hill Bay. Several thousand scallops were counted when spat bags were retrieved the following spring.
The technique for capturing sea scallop larvae is technically simple.
Morse explained that it involves deploying mesh spat bags on anchored lines about 15' off bottom to prevent predation and fouling, and 15' below the surface to prevent wave and storm damage as well as fouling. In the middle space, people have attached any number of bags, though a general rule is one every 6'-10' or so. The lines have a toggle buoy above the topmost bag, to keep the line upright, and some sort of buoy at the surface. Many fishermen have used their lobster buoys.
A spat bag needs to provide a large enough surface area to which scallop larvae can attach their byssal threads. The Japanese started in the 1930s by using an onion bag filled with cedar branches.
These days, fishermen in Maine use mesh bags that bear a striking resemblance to onion bags and fill these with Netron (a polyethylene material) to increase surface area. The mesh of the bag needs to be fine enough to prevent the growing larvae from falling out and, at the same time, protect the larvae from predators such as sea stars.
Each bag with its Netron cost about $2. Fishermen involved in the project already have much of the other equipment, such as line, that's needed. No vessel retrofitting is required, though it helps to have a pot hauler or other lifting device to retrieve the gear.
The bags are deployed about 40 days after spawning, which is generally in early September. Fishermen have used their knowledge of scallop beds to set the collection bas in likely spawning locations.
The bags could be then left to overwinter. But because the areas for setting are either in likely scallop tows (the Maine season starts Dec. 1) or exposed areas, the bags have been moved to safer bottom for the winter.
Site specific
Technologically simple, yes, but spat collection is extremely site specific and time sensitive. If the spat collectors are deployed too early, then predatory sea stars will settle in the bags and prey freely on the scallops. Will Hopkins of CBRC added that, in many areas, blue mussels and arctic clams often settle onto the bags as well, decreasing the space available for sea scallops.
If the spat collectors are deployed too late, the spat may be entirely missed and the bags become dirty and less effective.
Location is as important as timing. For example, less fouling occurs if areas between two land masses are avoided.
Leslie-Anne Davidson, a scallop biologist and the scallop project leader with Canada's Department of Fisheries and Oceans, said "Spat bags are hotels for scallops. When the bags are dirty, all the rooms are booked up."
In Japan, over 50 years of research has enabled scientists and fishermen to predict within hours when to deploy spat bags to capture the most spat. In Maine., there are still many questions to answer before such precision will be possible.
Researchers and fishermen alike are exploring scallop biology and which environmental factors trigger spawn. A model has been developed in the Cobscook Bay region to use science to predict spawn. SFA has enlisted the help of the Beal's Island Regional Shellfish Hatchery, Erin Fisher, and others to use this technique to predict spawning in the Stonington region.
Cobscook Bay, ME
In September of 1999, a scallop spat collection project was launched in Cobscook Bay, which widely known as the last great grounds for wild harvested scallops in Maine, and the idea is to keep it that way. Hopkins joined forces with Brian Beal, professor of marine ecology at UMaine at Machias and with BIRSH, early on to research some fundamental questions about scallop spawning.
In 1999, one month before deploying the spat bags into bay waters, scallop divers collected the first in many samples of adult sea scallops from Downeast Maine. These were used to establish what Hopkins described as "spawning readiness."
According to Beth Starr, BIRSH manager, identifying spawning readiness requires developing a gonad index, a visual exam to estimate when scallops are ready to spawn based on the color of the gonads and the size or weight of the gonad in relation to the entire body weight of the scallop. This gonad index study, recently funded by the National Fish and Wildlife Foundation, is crucial to help determine when exactly to deploy spat bags.
By looking at the gonad index in captive broodstock, Starr said it's possible to help estimate when scallops in the wild are ready to release eggs and sperm into the water column. The time to deploy spat collectors can then be calculated, which has been determined to be about 40 days after spawn.
So far, the Stonington scallops are arriving a spawning readiness earlier than those in Cobscook Bay. Starr said this could be due "to water temperatures as a result of circulation, phytoplankton, or you take your pick from all the ocean variables it could be."
Hopkins agreed that results are very site specific but added, "Everywhere the questions are the same, so we have to work together."
Saco Bay, Maine
Saco Bay on the New Hampshire border is now the third region in Maine where scallop spat collection projects are under way.
Carla Morin of the Northwest Atlantic Marine Alliance (NAMA) said that Saco Bay is a historical scallop fishing ground but, as with other historical fishing grounds, stocks are currently low. Predator-prey relationships, water quality issues, overfishing, or any combination of factors could contribute to decline.
Morin explained, "We just don't know why the beds aren't producing as much as they used to."
So, in addition to collecting spat, NAMA is partnering with the University of New England to determine what role water quality plays in scallop decline.
With a long-term goal of reseeding scallop beds to aid in the species' recovery, fishermen and NAMA, deployed 700 bags in September 2000. Morin said that seven Saco-area fishermen (draggers, gillnetters, and lobstermen) decided where to deploy the spats bags. Fishermen also took charge of moving the bags during shrimp season to avoid damage.
"It is their project; we are just assisting them," Morin said.
So far, Saco Bay spat collecting efforts are proving effective. In February of this year, when five bags where subsampled, 8,479 scallops of about two-centimeter size were found. The challenge now is to identify where scallops eventually settle and grow into adults.
Next step
Spat collection efforts have been in the works in Maine for about two years with a clear long-term vision of reseeding wild beds. In late August, in fact, plans were underway in several ports for deploying bags.
But what comes next? The Science Side will look at the future of spat collection, scallop bed reseeding, and whether it can contribute to a sustainable scallop fishery in the next CFN.
