Verification of Atlantic sea scallop (Placopecten magellanicus) shell growth rings by tracking cohorts in fishery closed areas

Abstract

We tracked the growth of large cohorts of sea scallops ( Placopecten magellanicus ) at four sites located in areas closed to scallop fishing and compared the observed growth with that inferred from rings on sea scallop shells collected at the same sites. Stochastic growth transition matrices were constructed for each site based on the shell growth increments, assuming annual ring formation. These matrices were used to predict the annual growth of the scallops, which were compared with direct observations of growth obtained by repeated sampling. Additionally, the observed growth of the scallops was used to estimate the parameters of a stochastic von Bertalanffy model for each site, which were used to estimate the mean annual growth increments as a function of starting shell height. These were compared with the mean growth increments on the shells. There was a close correspondence, in most cases, between the observed growth and the growth inferred from the shell rings, implying that the shell rings were formed annually. The lack of fishing mortality in the areas meant that there was no confounding of size-selective fishing with growth and allowed us to track cohorts longer than would otherwise have been possible.