Recruitment failure of the bay scallop,Argopecten irradians concentricus, during the first red tide,Ptychodiscus brevis, outbreak recorded in North Carolina

Abstract

In the presence of the first recorded red tide (Ptychodiscus brevis) outbreak in North Carolina, autumn 1987 recruitment of bay scallops (Argopecten irradians concentricus) in the state’s most productive scallop beds was a virtual failure. Recruitment averaged across all of Bogue and Back sounds was only 2% of the mean of three previous red tide-free (control) years. Only from central Core Sound northward, where the red tide occurred later and not as intensively, was bay scallop recruitment normal (93% of control years). Mortality of adult scallops from early December 1987 to late January 1988, while red tide was at bloom concentrations but fishing was prohibited, was 21%. No comparable natural mortality data exist for control years because intense fishing mortality in this period is confounded with natural mortality. Data on abundance of articulated pairs of empty shells strongly suggest that the red tide caused mortality of both adult and newly recruited bay scallops. Bay scallop recruitment in autumn 1988 again failed to restock the traditionally productive scallop beds in western Bogue Sound and in Back Sound, perhaps because the only concentrations of spawners surviving the red tide in central Core Sound and further north were too far distant for successful transport of bay scallop larvae in sufficient abundance to these traditional beds. This potential explanation implies continuing impact of the red tide on North Carolina’s bay scallop fishery until spawning populations increase in Back Sound and western Bogue Sound.