© 2003 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Population dynamics and predictions in the Isle of Man fishery for the great scallop, Pecten maximus L.
Port Erin Marine Laboratory, University of Liverpool Port Erin, Isle of Man IM9 6JA, UK
*Correspondence to B. D. Beukers-Stewart; tel: +44 1624 831038; fax: +44 1624 831001. e-mail: brycebs{at}liv.ac.uk.
There has been a fishery for the great scallop, Pecten maximus, around the Isle of Man, since 1937. Research up to the end of the 1980s suggested that these scallop stocks were in continuous decline. The fishery is now largely dependent on the strength of each recruiting year-class, placing it at considerable risk from recruitment failure. This study utilised data on the spat settlement, age structure, abundance and commercial catch rates of scallops, collected between 1975 and 2001, to examine recent population dynamics and the potential for predicting future catch rates. Spat settlement was generally low, but there were two exceptionally strong year-classes. Surveys of the stock revealed high exploitation rates during each fishing season (November to May inclusive) with variable recovery due to recruitment by the following October. In 1997/1998, scallop catch rates reached a 20-year high on several grounds and have generally remained high since. The strong spat settlements in 1989 and particularly 1994 were largely responsible for recent rises in catch rates, although the maintenance of high catch rates between 1999 and 2001 has occurred despite poor spat settlement between 1995 and 2000. Within stock surveys, the density of 2-year-old scallops was generally an accurate predictor of the density of 3- and 4-year-old scallops, 1–2 years later. The nature and strength of these relationships varied considerably between fishing grounds due to spatial variation in both scallop biology and patterns of exploitation. Results from fishery independent surveys did not always correlate well with commercial catch rates, however, suggesting the need for an expansion of the survey on some grounds. Overall, our study indicated that current levels of exploitation appear to be sustainable in the Isle of Man scallop fishery. Our results also demonstrated that monitoring of both spat settlement and the abundance of juveniles has considerable potential for predicting future catch rates of commercial sized scallops.
Keywords: stock assessment, predictions, exploitation rates, recruitment, scallops, Pecten maximus, Irish Sea
Received 8 July 2002; revision received 4 December 2002; accepted 6 December 2002.
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