Application of a Biomass Size Spectrum Model to Demersal Fish Data from the Scotian Shelf

Abstract

The distribution of biomass density over organism body size follows an orderly pattern in aquatic ecosystems. A recent theoretical model of such aquatic biomass size spectra predicts an overall primary slope across all trophic groupings in an ecosystem, attributable to physiological causes, and a set of secondary slopes of the biomass size spectrum, thought to be related to predator-prey interactions. Inter-annual variability in demersal fish biomass size spectra from 1970–1991 on the Scotian Shelf was assessed using fits of secondary slope derived from this model. The model was able to pick out 1976 as an anomalous year, when squid abundance on the Scotian Shelf was very high. Similarly, it was shown that the fitted slope of the curve was stable after 1980, a fact that may reflect fisheries management practices implemented in the late 1970s. How the fitted slopes to dome shaped biomass size spectra reflect the food resources available on the Scotian Shelf is discussed.