Temporal variability of total biomass in harvested communities of demersal fishes

The biomass variability of the demersal fish communities of the Bay of Biscay and the Gulf of Lions is analysed on a decadal scale using scientific surveys and fisheries data. The coefficient of variation of the total biomass is lower than the coefficient of variation of species biomass in both areas. Previous analyses from the Scotian Shelf have demonstrated that the total biomass of demersal fish is quite stable relative to individual species biomass. This result was interpreted as demonstrations of interactions between species due to energy limitation of systems. Moreover. the total biomass variability is lower in the Bay of Biscay than in the Gulf of Lions. As the distribution of the coefficients of variation of species in the Bay of Biscay does not differ from that in the Gulf of Lions, the difference of total biomass variability is not explained by the variability of species. Further, harvesting is investigated as a source of difference of total biomass variability between the Bay of Biscay, the Gulf of Lions and the Scotian Shelf. The mean of total biomass is the lowest in the area where the harvesting level is the highest (Gulf of Lions) and is the highest where harvesting is the lowest (Scotian Shelf), while the total biomass variability increases with the harvesting level. A hypothesis on fishing impact on the community dynamics is discussed and the total biomass variability is proposed to be a broad indicator of the fisheries impact on the demersal fish communities. (C) 2001 Elsevier Science B.V. All rights reserved.