Adding value to live, commercial size soft-shell clams (Mya arenaria L.) in Maine, USA: results from repeated, small-scale, field impoundment trials

The soft-shell clam (Mya arenaria L.) fishery in the state of Maine, USA, is worth $5–10 million annually and is primarily based on the sale of live individuals. More than 80% of the catch is sold for the “steamer clam” market that is highly seasonal due to supply and demand. Prices paid to harvesters for live clams throughout the year increases by as much as 70% during a 4-month period between early spring and late summer. If clams harvested in the spring could be held until late summer, a value-added product could be developed in this fishery. From April to August 1996, at an intertidal and subtidal location in eastern Maine, I tested whether it was biologically feasible to impound commercially harvested clams (shell LENGTH=44–75 mm) at densities between 720 and 850/m² using cages and nets (1.12 m²) to protect animals from predators. Survival was 91.7% (n=12) and 91.6% (n=6) at the intertidal and subtidal site, respectively. There was no discernible shell growth during this period and there was no difference between initial and final clam weights. The methodology was transferred to commercial harvesters in two Maine communities: Wiscasset (1997 and 1998) and Perry (2000). Impounded clams (=21.8 kg/cage; n=18) lost, on average, 5 kg/cage in 1997 and 1998, whereas no significant net loss in wet weight occurred in cages deployed in 2000 (=23.2 kg/cage; n=3). Differing harvesting and handling methods of individual clammers, prior to impounding clams, likely explains the variation in weight lost during the impounding periods. The difference in price per live kilogram between the beginning of the impounding period and the August sale date resulted in an average gain of $13.60/cage for clammers in 1997 and 1998 and $57.73/cage in 2000. Simple culture techniques can be used to increase the value of the live harvest of soft-shell clams along the coast of Maine. Clam impoundments may be a way for communities that co-manage the public clam resource with the state's marine resource agency to generate funds to pay for traditional management schemes, as well as enhancement programs that employ hatchery-reared juveniles. In addition, an indirect benefit of clam impoundments might be to create spawner sanctuaries since animals are impounded during the time when gamete release occurs.