Ecology of the Imperiled Grass Pickerel (Esox americanus vermiculatus) in Ontario: Distribution Patterns and Population Decline

Abstract

Freshwater fishes are among the most imperiled organisms on Earth and understanding their life history is vital to conservation efforts. Grass Pickerel, a top predator, is a nationally imperiled fish that is found at the northern edge of its range, has a highly patchy distribution, and can be rare to abundant where found in Canada. The distribution of Grass Pickerel within a watershed was explained using generalized linear models and is largely driven by site-scale variables such as ample submerged aquatic vegetation, channel cover, and associated wetlands in the floodplain, but regional factors, presumably climate, appeared important as well. Additionally, Grass Pickerel has declined in an eastern Ontario population since 1960 and forage fishes have increased in richness and abundance. Changes in the fish community were evaluated using non-metric multidimensional scaling and are likely due to combined effects of land use changes and alterations to stream hydrology from beaver activity and variable climatic conditions. The results from this study are informative for habitat protection and mitigating threats to this species, but also make a case for improved, standardized monitoring and baseline data. Grass Pickerel populations in Ontario are at the periphery of the species’ range and are, perhaps, the most important for the species persistence in a changing world.