Northern New England's threatened soft-shell clam populations

Abstract

Commercial exhaustion of soft-shell clam,Mya arenaria, had become the fate of many potentially productive clamming areas along the coasts of Massachusetts, New Hampshire, and southern Maine. Investigations of a particularly severe case of soft-shell clam stock depletion in Hampton-Seabrook estuary, New Hampshire, indicated that by 1976 human diggers had removed approximately 87% of the adult clam resource that had existed in 1971. Meanwhile, circumstantial evidence strongly implicated the green crab,Carcinus maenas, as responsible for successive stock recruitment failures, these crabs having consumed most of the young seed clams before they could grow to harvestable size. In 1976, this apparent population imbalance may have been at least partly redressed by a prodigious spatfall, resulting in a massive and widespread reseeding of many flats along the northern New England coast. Spat, or seed clam, densities of up to 1,700 individuals per square foot, over areas of several acres, have been observed. Those clamming areas where aggressive predator control programs had been instituted exhibited the most favorable response in terms of seed clam survival and growth. Evidence also indicated that crowding in thickly seeded portions of the clam flats inhibited shell growth.