Projected impacts of climate change on three freshwater fishes and potential novel competitive interactions

AimAs global air temperatures continue to rise in response to climate change, environmental conditions for many freshwater fish species will change. Warming air temperatures may lead to warming lake temperatures, and subsequently, the availability of suitable thermal habitat space. Our objectives are to identify the responses of three fish species from three thermal guilds to climate change in Ontario and consequently, the potential for novel competitive interactions between two top predators. We focus on lakes in Ontario because it is a dynamic region that encapsulates the northern and southern range extents of warm and cold-water fish species. LocationOntario, Canada. MethodsUsing lake morphology, water chemistry, climate and fish occurrence data for smallmouth bass (warmwater predator), walleye (coolwater predator) and cisco (cold-water forage fish), we modelled the occurrence rates of three fish in 2050 and 2070 under 126 scenarios of climate change. We also calculated the percentage change in co-occurrence of walleye and smallmouth bass in 2050 and 2070. ResultsSmallmouth bass occurrence rates were predicted to increase by similar to 306% (ranging between 55 and 422%) by 2070 relative to their current distributions. Walleye were projected to decline by 22% (-42 to a +6% change) and cisco by 26% (-7 to -47%) by 2070. By 2070, walleye-smallmouth bass co-occurrence was predicted to increase by 11%, with walleye in central and northern Ontario at greatest vulnerability due to increased competition with smallmouth bass. Main conclusionsThese results highlight three unique responses to climate change: range expansion, northward range shift, and range contraction for warmwater, coolwater and cold-water fish species, respectively. Alterations in distributions of these three ecologically important fish species may lead to shifts in fish community structure and novel species interactions in Ontario lakes, exacerbating the vulnerability of native coolwater predators to climate change.