Diet of demersal fish species in relation to aquaculture development in Scottish sea lochs

The diets of demersal fish, principally haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and several flatfish species, sampled from four Scottish sea lochs (Hourn, Kishorn, Duich and Nevis) which support aquaculture sites, were examined in order to determine whether the impact of aquaculture on benthic biodiversity would affect the diets of demersal fish. Loch Kishorn had the highest maximum planned aquaculture production, loch Nevis follows and lochs Hourn and Duich have the lowest planned production. Samples were collected from locations less than and more than 2000 m from fish farm cages. Fish close to the fish farm cages were on average of greater individual weight than those further away from fish farms. Haddock ate predominantly Malacostracan crustacea, Ophiurid echinoderms and Polychaete annelids; whiting ate predominantly Malacostracan crustacea and teleost fish and flatfish ate Malacostracan crustacea, Polychaete annelids and Ophiurid echinoderms. A small number of saithe sampled had eaten mainly fish farm pellets. Dietary variation in each species was analysed in relation to loch, proximity to aquaculture facilities and fish size. Diet of whiting varied with body size. Dietary differences were observed between the lochs and between sites close to and far from farms in two lochs although these differences cannot be specifically attributed to aquaculture development. Controlling for differences between individual lochs, proximity to aquaculture facilities did not consistently affect diet composition.