Archives: Fall 2000/Winter 2001 Table of Contents
The Waiting Game: Judging the Success of Bay Scallop Restoration on Cape Cod
by Tracey Crago, WHOI Sea Grant

If only time will tell, the 2001 bay scallop harvest in select Cape Cod locations will have a message for Dale Leavitt and Diane Murphy. But it isn’t words they are hoping for come October, it’s bay scallops. Lots of them.

Leavitt, the fisheries and aquaculture specialist for WHOI Sea Grant and Cape Cod Cooperative Extension (CCCE), and Murphy, CCCE marine program associate, have spearheaded a bay scallop restoration program on Cape Cod that is modeled after similar programs in Maryland, Florida, and New York.

The program, designed strictly as a fishery restoration project, is funded mostly by Barnstable County with additional support from WHOI Sea Grant and AmeriCorps. Similar to an aquaculture operation, minus the final controlled grow-out and harvesting steps, the program uses spawning sanctuaries.

Bay scallops are being removed from spat bags to be placed in floating cages fro the grow-out phase. Photo: R.Karney/M.V. Shellfish Group.

The process starts with bay scallop juveniles, called "seed," derived from local broodstock and produced by commercial hatcheries (in this case, ARC Corp. in Dennis, MA, and Mook Seafarm in Maine). The seed are placed in bags and put into bottom cages, where they are kept over the winter. In the spring, the crop of bay scallops is thinned out so that densities in the spawning cages are less than that of the over-wintering cages. This allows for the faster growth that occurs in warmer waters with greater food supply. The spawning cages, which float, are deployed in early summer. While deployed, the spawning cages must be maintained, which involves cleaning and removing fouling organisms, and checking for predation and loss, and later, gathering samples to check for gonad development. This indicates when the scallops are about to spawn. In mid-summer, spat collectors are deployed to monitor the amount of spat released into the waters surrounding the cages. The spat bags—actually plastic mesh bags—offer the larvae a suitable substrate on which to settle.

Now in its second winter, the program applied lessons learned in the first year to narrow the focus from nine original over-wintering sites to five, in the towns of Barnstable (West Bay), Chatham (Ryder’s Cove), Falmouth (West Falmouth Harbor), Orleans (Frostfish Cove), and Yarmouth (Bass River). Two new sites were added this year: Bourne (Monument Beach) and Eastham (Town Cove). The two sites that were dropped had low survival rates, ranging from 16 percent to just under 50 percent. The cutoff, says Leavitt, was anything over 60 percent.

"A lot of people were telling us that getting over-wintering survival rates of 25 percent would be lucky," recalls Leavitt, "and that survival would not be high enough to warrant the time and energy the project would require." There were optimists too, who lobbied for sites in their towns that they believed would offer survival rates as high as 90 percent—consistently. And, given results from the first year, they were right. "Survival was highest in places where we predicted it would be high," says Leavitt. Of course, with only one winter behind them, Leavitt and Murphy aren’t ready to draw any conclusions. Like most shellfish stocks, harvests can vary dramatically from season to season.

Though Yarmouth shellfish constable Conrad Caia missed the "banner year" for bay scallops in 1992, he’s been told that Yarmouth bay scallopers pulled 4,000 bushels from town waters that year. Caia says that since 1996, when he arrived on the job, Yarmouth’s catch has remained steady at around 1,000-plus bushels, generating roughly $100 per bushel for harvesters.

As a participant in the restoration program, Caia faced one of its more difficult challenges last winter: ice. "We had floating cages in Bass River last year. I’d have to go out and chop the ice around the cages twice a day." (Once the ice thawed, they converted to bottom cages.) But he was rewarded with a survival rate of 63 percent and deployed those scallops in spawning cages in Lewis Bay. Caia released the adults just a few months ago, in October, and is eagerly awaiting next year’s harvest. And he’s started work on future years as well, having deployed seed scallops in cages in Bass River. "Only this year," he says, "we’re using bottom cages."

Fellow shellfish constable Paul Montague, of Falmouth, also participates in the restoration program. He reasons that, with scallop populations down Cape-wide, this project will only help to get areas going again that were once productive. Montague admits to being "very surprised" by the over-wintering results of the first year, particularly in one of his sites, West Falmouth Harbor. "I had my doubts," he says. "The whole time [they were there] I kept looking, saying ‘I don’t know…’ The success was outstanding." Indeed, 79 percent of the scallops that spent the winter in West Falmouth Harbor survived.

In terms of over-wintering survival in the first year, and the ability to get those scallops to spawn, the program has been a success. "A lot of the objectives have been met," says Murphy. As for tracking success, "that needs work for future years. We’d like to do some genetic fingerprinting to follow the animals that we’re supplying. Knowing the genetic background of the broodstock is crucial to our ability to show results," she explains.

A WHOI Sea Grant supported project led by Alan Kuzirian of the Marine Biological Laboratory succeeded in developing a genetic marker for bay scallops. The restoration project is now over-wintering offspring of Kuzirian’s genetically identified or ‘fingerprinted’ scallops (see Two if by Sea, Vol. 2(3)). In the summer of 2001, the survivors will be planted at a site yet to be determined, where they can be monitored. Eventually, Leavitt and Murphy will look for third generation offspring of Kuzirian’s fingerprinted scallops in the field.

While waiting for genetic proof of the project’s success, the anecdotal evidence has kept spirits high. Program participants are willing to attribute, at least in part, strong sets of bay scallops to the spawning sanctuaries. Henry Lind, Eastham Natural Resources officer, told Murphy he hadn’t seen that much natural set in five years.

"There has been a lot of learning this year; it was very labor intensive," says Murphy. "Fouling [on cages] was a problem [at some sites] and it made it difficult to deal with equipment. We’re not sure of the effects on the animals. They grew; their gonads and adductor muscles are comparable to others, so…"

Leavitt shares Murphy’s hopes for the success of the restoration project in large part because of what it will mean for the region. But knowing that the key to assessing the program lies in the genetic fingerprinting techniques means more waiting—and probably some luck as well.

"Any time I’ve played with scallops it seems likes it’s an incremental thing," says Montague. "[You get] some the first year, more the next, and so on…until you have a crash and no one knows what happened. I honestly believe no one knows the secret of scallops."

Unlocking that secret may be one reason why Montague and Caia are committed to making the program as successful as Mother Nature will allow. "It’s an excellent program," says Caia, "and I’m willing to do anything I can to keep it going."