SIZE COMPOSITION AND POT SELECTIVITY IN THE LOBSTER (HOMARUS-GAMMARUS (L)) AND CRAB (CANCER-PAGURUS L) FISHERIES ON THE EAST-COAST OF ENGLAND

The size composition of lobsters and crabs caught in the north Norfolk fishery differs markedly from that of other parts of the east coast of England. Previous studies indicated that substrate type and pot selectivity, in addition to the pattern of exploitation, account for the small individuals caught in Norfolk. Experimental fishing comparing fine-meshed small-ringed Norfolk pots and Yorkshire parlour pots was carried out off Cromer in north Norfolk and in Bridlington Bay, Yorkshire. Analysis of size composition of catches showed that both lobsters and crabs retained by the Norfolk pots were significantly smaller than those retained by the Yorkshire pots. The replication of the experiment in two fishing areas allows comparison of their size compositions when any effect of pot selectivity is equal in the two areas. The smaller size composition of lobsters caught in the Norfolk fishery was partially attributable to pot selectivity and partially due to real differences in size composition of the populations on the ground. For crabs there was little or no difference between the Norfolk and Bridlington Bay fisheries when the effect of pot selectivity was equal in the two areas. As the residual differences in lobster size composition were predominantly below the minimum legal size (and hence not subject to fishing mortality), the results suggest that on the east coast of England size compositions of lobsters are influenced by substrate type to a greater extent than those of crabs. © 1991 Conseil International pour l'Exploration de la Mer.