Response of Brook Trout (Salvelinus fontinalis) to critically high-water temperatures in streams with physical barriers.

Pelletier, Corey*^1,2, Graham Forrester², Ellie Madigan², Richard Mercer², Carissa Charbonneau¹, Mitchell Parizek¹, ¹RIDEM Division of Fish and Wildlife, West Kingston, RI, University of Rhode Island, Kingston, RI, ²University of Rhode Island, Kingston, RI

In New England, relic dams, perched culverts, and other physical barriers are commonplace in small streams where Eastern Brook Trout and other at-risk species reside. Collectively, these structures impede the ability of aquatic organisms to access essential habitats. As water temperatures gradually increase due to climate change, coldwater-dependent fishes are at increasing risk of exposure to thermally stressful or even lethal temperatures. We tested whether physical barriers in streams restrict movement sufficiently to compromise the ability of trout to access cool water thermal refuges. Using radio telemetry, brook trout were tagged with VHF radio tags and tracked throughout the upper reaches of two HUC-12 watersheds. Trout were tagged in four stream reaches with varying distances to upstream and downstream barriers. Fish were tracked weekly via mobile telemetry. Habitat selection was assessed by quantifying conditions at sites occupied by fish and a set of randomly selected locations. Habitat variables included temperature and other stream features known to influence brook trout fitness. Preliminary analyses suggest that brook trout in warmer stream reaches were more likely to make substantial downstream movements in early summer and some traversed barriers in doing so. Most trout were able to avoid dangerously high temperatures (above 25 C) but this required more active habitat selection in warmer stream sections. Subsequent work will test for longer-term consequences on those that move larger distances in warm-water reaches and the effects of traversing barriers that may only be intermittently passable, or passable in one direction only.