The effect of fishing on demersal fish community dynamics: an hypothesis

Abstract

Fishing acts like a predator; it alters the extent of competition and allows the coexistence of competitive species. To test this hypothesis, several component elements are addressed. The variability of biomass in demersal fish communities is analysed to seek evidence that biotic interactions play a role in community dynamics. Spatial segregation as a result of a fishery's removal in several communities is analysed to test whether there are differences in coexistence or segregation. Previous studies of the demersal fish community of the Scotian Shelf revealed that the coefficient of variation for total biomass over time was lower than that for individual species. Similarly, as shown in this paper, variability of biomass in the demersal fish assemblages of the Bay of Biscay and the Gulf of Lions (France) are characterized by the same patterns. This pattern is interpreted as the effects of interactions between species (predation, competition) that involve energy limitation within the systems. Also, spatial segregation among species is related to fishing intensity. First, differences in spatial segregation between the Bay of Biscay and the Gulf of Lions, as measured by the slopes of the species area curves, are significant. Spatial segregation decreases from the least harvested systems to the most harvested ones when data from several systems are compared. These analyses indicate that biotic interactions play a significant role in the dynamics of demersal fish communities and that decreases in the spatial segregation of species can be associated with increased fishing. These results are consistent with the hypothesis that fishing and predation have similar effects on fish communities.