Predation by the Oystercatcher, Haematopus ostralegus (L.), in Relation to the Cockle, Cerastoderma edule (L.), Fishery in the Burry Inlet, South Wales

Abstract

Oystercatcher feeding responses and a mathematical model of the cockle fishery and bird predation [South Wales] are presented. A complex spatial pattern of predation by the oystercatchers appeared linked to the density of the cockle stocks; the earlier conclusion that most (up to 90%) of the 2nd-winter cockle mortality was attributable to oystercatchers does not seem to hold for the cockle population as a whole. Further, the densities of 2nd-winter cockles were much less variable after winter predation than before, both within and between winters, indicating that there was a level at which the birds turned to other prey. The model gives values of equilibrium yields of cockles for a range of fishing effort and strategies, bird numbers and feeding thresholds. The effects of variations in all of these are discussed in relation to the yield of cockles and stability of the fishery. Further studies are advocated on the nature of the threshold which appears critical to the stability of the fishery under intense predation and fishing.