Fish Assemblages in Subarctic Lakes: Does Fire Affect Fish–Environment Relations in Northern Alberta?

Abstract

In 1995, a wildfire swept through a large area of the Caribou Mountains, a remote subarctic plateau of northern Alberta, Canada, containing numerous unstudied and unexploited small lakes. To assess near-term effects of fire and to establish information on assemblage–environment relations in this previously unstudied region, we sampled lakes in burned and unburned (reference) catchments within 2 years of the fire. To further understand species–environment relations in these small, subarctic lakes, we also compared aspects of their fish assemblages with those of assemblages in previously studied lakes of similar sizes in the boreal mixed-woods region to the south and in several large Caribou Mountain lakes. Correspondence analysis revealed three simple but distinct small-lake fish assemblages in the Caribou Mountains: those dominated by northern pike Esox lucius, suckers Catostomus spp., or Arctic grayling Thymallus arcticus. Canonical correspondence analysis revealed significant species–environment relations, but there was also some evidence that biotic interactions contributed to these assemblage types. Despite its extensiveness (84% of catchment area disturbed), fire did not appear to impact fish assemblages in burned lakes. Percentage disturbance accounted for less than 10% of the variation in fish assemblage structure among lakes, and reference and burned lakes were represented among all three assemblage types. However, burned lakes had fewer small northern pike than did reference lakes, suggesting possible effects of fire at the population level. Large Caribou Mountain lakes had a higher species richness and a distinctive species pool, reflecting important limnological differences with their neighboring small lakes. Despite a smaller regional species pool, the small Caribou Mountain lakes displayed local richness that was comparable to similarly sized lakes in the boreal mixed-woods region. Also comparable was the limited near-term effects that catchment-level disturbance had on the resident fish communities in small lakes of both regions. Population-level differences between disturbed and reference lakes, however, suggest that longer-term impacts are possible.