Impact of piscivorous fish introductions on fish species richness of small lakes in Gatineau Park, Québec

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Abstract
Fish communities of small lakes (< 61 ha) of Gatineau Park (Québec, Canada) which, originally lacked piscivores, were studied to assess the impact of piscivorous fish introductions over the past 85 years. Total species richness was not significantly different between lakes with (n = 15) or without (n = 22) introduced piscivores. However, small-bodied species richness (mainly cyprinid) was significantly lower (nearly half) in lakes with piscivores. Lakes with piscivores showed communities dominated by large or deep-bodied species (mainly Catostomidae, Percidae and Centrarchidae) whereas lakes without piscivores contained mostly small-bodied species (mainly Cyprinidae, Umbridae and Gasterosteidae). Few relationships were found between morphometric variables and fish richness variables. Total fish species richness was found to be a positive function of area and a negative function of elevation when all lakes (n = 45) of the park are considered. For the small lakes of the park, small-bodied species (and cyprinid species) richness in lakes without introduced piscivores was inversely related to the elevation of the lake. Such a relationship was not observed for small lakes with introduced piscivores, possibly because of the disruptive effect of piscivores on small-bodied species number. These results suggest that piscivory by the introduced species is probably responsible for the local extinction of many small-bodied species. Long-lived large-bodied and deep-bodied species (often with spines) are better able to withstand intense predation pressure due to their large size and the dissuasive effects of spines on fins. Because five native small-bodied species were found only in lakes lacking piscivores, it is predicted that their local extinction would occur if introduced piscivores establish populations in these lakes. Thus, small piscivore-free lakes with high small-bodied fish species diversity should rank high on the conservation priority lists of north temperate parks in order to maintain native fish biodiversity.

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