Spatial segregation among fishing vessels in a multispecies fishery

Abstract

Individual decisions of fishers on where to fish in heterogeneous environments may shape the relation between fishing effort and fishing mortality. Fishers may be viewed as individual foragers, whose decisions are aimed at optimizing short-term gain, as in ideal free distribution (IFD) theory. Although IFD assumes all foragers to be equal, they are likely to differ in competitive abilities for different prey types or target species. Here, we present an IFD-like model of a fishing fleet consisting of two components with different competitive abilities for two target species, showing that spatial segregation can result from unequal interference competition, but also in the absence of interference competition. Differences in catch efficiency between vessels for target species in combination with differences in the spatial distribution of target species can result in spatial segregation among vessel groups. The theoretical results are used to interpret the observed spatial segregation of two components within the Dutch beam trawl fleet using observations from a vessel monitoring by satellite system. However, this study cannot pinpoint which of the processes included in the theoretical model is the prime cause of the segregation within the Dutch beam trawl fleet. © 2009 International Council for the Exploration of the Sea.