Recruitment overfishing in a bivalve mollusc fishery: hard clams (Mercenaria mercenaria) in North Carolina

Abstract

Because of their high fecundity, marine invertebrate fisheries are rarely considered at risk to recruitment overfishing. This presumption can be criticized on population theoretic grounds and conflicts with growing evidence of recruitment limitation in a variety of marine invertebrate populations. Sampling in 11 years spanning a 24-year period from 1978 to 2001 reveals that hard clam (Mercenaria mercenaria (L.)) recruitment declined significantly by 65–72% within the fishing grounds of central North Carolina. This 24-year period began when high demand and prices drove increased clamming effort. Accordingly, landings grew rapidly 5-fold, a yield that was not sustained and subsequently fell by over 50% from 1983 to 2000. Fishery-independent sampling repeated identically in three representative habitats demonstrates declines of 17, 79, and 95% in hard clam density and of 24, 46, and 83% in spawning stock biomass during the 18+ years of 1980–1997. Small-scale experiments and measurements in depleted habitats show no compensatory enhancement of hard clam recruitment with local reduction in adult density. Consequently, the hard clam in North Carolina serves as perhaps the most compelling example of unsustainable fishing mortality leading to recruitment overfishing in a bivalve mollusc stock. Spawner sanctuaries could serve to restore and protect spawning stock biomass in this and other invertebrate fisheries.