R-12-01 Spatial and temporal variation in the growth of the soft-shell clam along the coast of Maine

William G. Ambrose, Jr.
Professor of Biology
Bates College
Lewiston, ME 04240

Brian Beal
Professor of Marine Ecology
University of Maine at Machias
Machias, ME 04654

Soft-shell clams (Mya arenaria) are one of the most important commercial marine species harvested in Maine. In the last decade, clam landings averaged $14 million a year to harvesters, and nearly $40 million annually to the state economy. Clams are also unique in that they are co-managed by the state and local municipalities or regional harvester committees. This is one of the oldest such co-management programs in the United States.

Over the past 25 years, the average seawater temperature in Maine during winter months has risen steadily, facilitating an increase of the invasive green crab which prey on soft-shell clams and other important commercial species. During this same period, clam landings decreased by nearly 75%.

Knowing regional and local estimates of clam growth—how quickly stocks will reach commercial size—can help communities improve the way they manage the resource. Ambrose and Beal examined growth rates of wild clams and followed the growth of hatchery-reared juveniles in the wild in different geographic regions of the coast and at different tidal heights. Beal also worked with the Maine Clammers Association (MCA) to examine the effectiveness of different methods to protect shellfish from green crabs and other predators with the goal of enhancing shellfish populations.

Through four years of extensive field research (6 experiments per year, many duplicated in different locations) the project demonstrated adaptive shellfish management practices that are assisting the fishery adjust to changing environmental conditions. The findings and clam protection techniques learned from the field research has led at least four clammers to begin the process of starting their own individual shellfish protection projects (“farming”) and various towns (Freeport, Brunswick) have or are considering intertidal leasing options and/or ordinances which allow investments made by individuals partaking in clam protection methods to be protected.

Two-year project; total Sea Grant funds: $147,473