A summary of the effects of climate change on Ontario's aquatic ecosystems.
Climate change will alter Ontario's aquatic ecosystems as a result of increases in air and water temperature, decreases in ice and snow cover, and changes in the timing and amount of precipitation. These changes will affect the hydrological cycle by altering the flow of water and water chemistry. Threats to freshwater fauna include nutrient enrichment, hydrological modifications, habitat degradation and loss, pollution, and the spread of invasive species. A changing climate and increasing levels of ultraviolet light pose additional risks that add to existing threats. The combination of changes in land use, habitat, and climate present a serious challenge to the long-term integrity and health of aquatic ecosystems. Since fish are cold-blooded, increases in water temperature will affect their distribution, growth, reproduction, and survival. The habitat and productivity for coldwater species, such as lake trout (Salvelinus namaycush) and brook trout (Salvelinus fontinalis), may decline substantially with increased air and water temperatures. Coolwater fishes likely will respond to climate change in a variety of ways. For example, in the case of walleye (Sander vitreus) in central and northern Ontario, warming may increase available habitat. Overall, model projections suggest a northward shift in the location of the walleye fishery. Many warmwater fishes are projected to benefit from warmer water temperatures. For example, smallmouth bass (Micropterus dolomieu), which reach the northern extent of their range in Ontario, may expand northward as warmer water temperatures facilitate increased growth and recruitment. A northward expansion of warmwater fish species will disrupt the life history strategies of cool- and coldwater fish species. Commercial and recreational harvest opportunities for lake trout, brook trout, and perhaps walleye will decline, particularly in southern Ontario. Although these losses may be offset somewhat by increased opportunities to harvest warmwater species, the expected changes in fish communities will bring a variety of social and economic challenges. To meet these challenges, an adaptive approach to fisheries and aquatic ecosystem management in Ontario is needed. Known and potential climate change effects must be incorporated into existing fisheries management plans and strategic plans will need to be revisited to ensure that they reflect anticipated changes. Given the importance of understanding the range of potential climate change effects on aquatic assets, it is essential that management agencies and organizations identify and apply appropriate effective mitigation and adaptive management strategies. This report reviews and summarizes the known and potential effects of climate change on Ontario's aquatic ecosystems and on the life history of selected coldwater, coolwater, and warmwater fish species.