Research Document - 2003/073

Using density-fish size relationships to predict the habitat area of species-atrisk in the Great Lakes

By Randall, R.G. and Minns, C.K.

Abstract

Fish catch in numbers per transect was negatively correlated with average fish size in samples from different habitats in near shore areas of the Great Lakes. Density-fish size relationships for the whole fish assemblage and for individual species indicated regression slopes that were not significantly different from -0.9, consistent with the energetics-equivalence hypothesis, but the elevations were habitat dependent. For example, the average density of Perca flavescens and Lepomis gibbosus, adjusted for fish size, was about two times higher at coastal wetlands than at harbours. The inverse of the density-fish size relationship can be used to estimate the area per fish in each of the habitats. A preliminary predicative equation was: loge Area = 0.29 + 1.02logeWmat + 0.69Capacity, where Area was the area per fish (m2), Wmat was weight-atmaturity (g), and Capacity was a habitat capacity factor (1 for moderate and 0 for good habitat). Based on this equation, the area needed for a hypothetical species that matures at 50 g, assuming a population size of 7,000 fish and assuming good habitat capacity, was calculated to be about 78 ha. To make the predictive model broadly applicable, more research is needed to quantify the use of different habitats at different life history stages.

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