SEA SCALLOPS: A NEED TO KNOW MORE
(Published in the Quoddy Tides, June 9, 2000)
Of the thirty-two species of filter-feeding marine animals that live in Cobscook Bay, the sea scallop is one of the more important ones to the local economy. Out of a desire to sustain this economic resource, and to avoid what has happened to other fisheries, local fishermen, researchers, and managers have begun exploring ways to better manage the scallop fishery. Key to these efforts is knowledge about the scallop as a species as well as an understanding of its place in the Cobscook Bay marine system.
Unfortunately, what we currently know about the population in Cobscook is meager.
"How can we manage a fishery when we don't know what's out there?" asks Brian Beal, a marine ecologist at the University of Maine at Machias and one of the few scientists in Maine who is working to expand that knowledge. "There are some fundamental questions that need to be answered, such as, where are they? how many? what size?"
He added, "Other questions come up repeatedly in discussions over the future of the scallop fishery - how fast do scallops grow to harvestable size? how soon are they replaced after harvesting? how many scallops should be left behind on the bottom for populations to recover quickly?"
We do know that scallops, as filter feeders, play an important role in the bay. They process huge amounts of water, filtering out nutrients to feed themselves. In doing so, they help keep Cobscook's nutrient rich system in balance.
We also know that the adult scallop is among the more mobile filter feeders in Cobscook Bay. By contracting its adductor muscle, the part that we eat, it can expel water out of its body in jet streams, sending the scallop backwards in the water. In this way it can escape predators or respond to environmental changes by migrating to a different area.
We know less about the reproductive habits of scallops. That knowledge could provide us with clues as to how easily the population can recover from harvesting and how we can perhaps "enhance" the scallop population. Some of Brian Beal's research focuses on these reproductive processes.
"Like the sea urchin, scallops reproduce, or spawn, by releasing eggs and sperm into the water column. The scallop has a higher reproductive output than any other shellfish except oysters, with females producing 50-75 million eggs and males producing up to 100 million sperm," Beal says.
Adult scallops are triggered to spawn by changes in seawater temperatures and by taking in external hormones associated with eggs and sperm that have already been released. Successful fertilization depends partly on how large the population is and how close individuals are to one another.
"Harvesters need to leave behind enough scallops and in close proximity for reproduction to be effective," Beal states. "Even when successful, less than 1% of fertilized eggs grow to harvestable size."
One way to increase the population, and thus harvests, is to enhance wild stocks. Beal is currently working with local fishermen, the Beals Island Regional Shellfish Hatchery (BIRSH), and the Cobscook Bay Resource Center on ways to accomplish this by protecting the early life stages of the scallop, particularly the juvenile scallops, called "spat."
Last fall, a handful of scallopers in the Bay collected wild scallop spat using mesh bags attached to anchored lines, a technique used successfully in Japan and Canada. They set out their spat collectors at several sites near Lubec, Eastport and Perry, with highly variable results. The goal is to protect the collected juvenile scallops during a very vulnerable time in their life cycle and then release them back into the Bay.
It is possible that efforts to collect wild spat might fail to produce an adequate supply for enhancement projects. As an alternative approach, Beal and others are working to produce spat in a hatchery setting by inducing adult scallops to spawn and then rearing their larvae. Local fishermen are also assisting with this research by collecting the adult scallops, or broodstock, for the project.
Beth Starr, the hatchery manager at BIRSH, explains some of what is being learned: "It's all about food - one part of the project focuses on feeding the scallop larvae to figure out what types of microscopic plants, or phytoplankton, they prefer to eat, what type they grow best on, and how this changes after they transform into the juvenile stage."
Scallop larvae swim around in the water column for six weeks, up to four weeks longer than other shellfish larvae. They eat a lot less food, and are more finicky about the type of food they eat.
"We have to be more careful with the larval stage of the scallop, since they spend so much time in the water column," Starr adds. "As for the food they eat, we have to focus on the quality of the food that's available, not so much the quantity."
With the exception of a tiny shell, the larvae look nothing like the adult. When the larval stage ends and they transform into juvenile scallops, the scallops attach themselves to hard surfaces on the sea bottom with a byssal thread, similar to mussels, that comes out of a gland in their foot. As the scallop grows to adult size, it detaches from the bottom and becomes much more mobile.
At the hatchery, the juvenile scallops are grown in a protected environment and then seeded on the bottom in the wild. Part of the research will be to determine what reseeding methods will result in the best survival rates.
The information that comes from efforts by fishermen and the researchers at BIRSH can be directly applied to fishery management.
"Even with the limited information we have now, managers can begin making changes," states Beal. "For example, if you increase efforts to protect scallop reproductive success and to protect juveniles, you've enhanced the fishery."
In addition to this developing partnership between fishermen and researchers, there are other signs that interest in improving scallop management is growing. The Department of Marine Resources recently sponsored a meeting in Machias to gather ideas from fishermen and other members of the public on research that is necessary to better manage Maine's scallop resource.
The combination of new research and new management strategies, with the direct involvement of fishermen in both, can help ensure that scallops remain an important resource to the local economy and a key player in keeping the Cobscook Bay system a healthy and productive place.
This column was prepared by Cheryl Daigle and Jim Dow. Cobscook Soundings was a monthly column produced by the Maine Chapter of The Nature Conservancy. Its purpose was to share what is known about the workings of the Cobscook Bay marine environment, so that all who make decisions about the use or care of the bay have the best available information.
Return to Cobscook Bay Resource Center homepage.