Effect of watershed size on fish biomass and species richness in Gatineau Park streams (Québec, Canada)

Twenty seven streams of Gatineau Park were sampled to examine how fish biomass and species richness vary with watershed size and to assess whether fish communities are affected by the presence of beaver dams on the streams. Fish biomass was sampled by electrofishing intensively from a 10 meter riffle segment at each site and biomass was estimated by the attrition method. Species richness was estimated from electrofishing a longer segment of each stream corresponding to a riffle-run-pool section. Species richness varied from 1 to 6 species and the most common species were creek chub (found at 52% of sites), brook trout (30% of sites) and northern redbelly dace (19% of sites). Biomass varied from 0 to 88.6 (g/m²). In watersheds ranging from 0.22 to 61.2 km², fish species richness increased with watershed area (R²=0.27, p=0.006) although biomass did not vary with watershed size. Similar species-area trends have been found by authors in European streams. The presence of beaver dams did not affect species richness or biomass.