Cephalopod consumption by trawl caught fish in Scottish and English Channel waters

Although there have been numerous studies on diets of fish from European waters, they are often of limited use for estimating the impact of fish predation on cephalopod resources. This is due to either the origin of the fish sampled, e.g. from areas with a relatively low cephalopod abundance, or to the method of prey identification: cephalopods are rarely identified to species. This paper presents a summary of recent sampling of the cephalopod species appearing in the diet of commercially important fish species in UK waters. Samples of demersal fish from around Scotland and from the English Channel were collected opportunistically during: research trawl surveys and from commercial trawlers in different seasons. For all fish species examined, incidence of cephalopods in the stomachs was low, with fish and crustacean prey dominating stomach contents. Most of the cephalopods found were species with little or no commercial value and small adult body size, such as the small loliginid squid Alloteuthis spp. and bobtail squid (Sepiolidae). Only during December 1998 were some commercially valuable squid (Loligo spp.) observed in fish stomachs, although in relatively small quantities and comprising mainly of pre recruit individuals. It is reasonable to suggest that most commercially fished teleosts have little direct impact on post-recruits of commercially important cephalopod stocks, although their impact on recruitment may be significant. The stomach contents data are used to provide a rough estimate of cephalopod consumption by cod populations in the study area and the use of such data to estimate natural mortality is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.