Behaviour and energetics of whelks, Buccinum undatum (L.), feeding on animals killed by beam trawling

Abstract

Whelks, Buccinum undatum, are potentially important scavengers of animals damaged or killed as a result of beam trawling. In order to assess the ability of whelks to scavenge these moribund animals, and the consequences of this to energy flow, we presented them with four different species that were either damaged on the seabed or died as a result of capture by beam trawling. Whelks ate swimming crabs, Liocarcinus depurator, purple heart urchins, Spatangus purpureus, and a gadoid fish, the pouting, Trisopterus minutus, but not plaice, Pleuronectes platessa. Whelks moved most rapidly towards swimming crabs, suggesting that these were the most preferred prey type. Although the rate of energy intake was highest when whelks fed on sea urchins, when fed to satiation they acquired most energy from swimming crabs. When presented with whole animals, whelks fed preferentially on different body tissues, e.g. they consumed the eyes of pouting first, and never ate the gills or carapace of swimming crabs. Absorption efficiency was highest when fed a diet of swimming crabs (93%) and lowest when fed pouting (83%). Whelks are able to efficiently utilise animals killed by beam trawling, and our results indicate that they prefer the most energetically rich species. In areas of intense beam trawling, such as the southern North Sea, dead or moribund animals which result from these activities could constitute a considerable proportion of whelk diets.