Brook Trout abundance and distribution at multiple spatial scales in Lake Superior tributaries

Abstract

Brook Trout (Salvelinus fontinalis) populations and habitat conditions are adversely affected by anthropogenic impacts that could impact abundance and distribution of Brook Trout at different spatial scales. My goal was to examine environmental DNA (eDNA) and underwater video cameras (UWVC) as alternative sampling methods to conventional (electrofishing) methods for measuring abundance and distribution of Brook Trout in stream environments across two sampling years (2019, 2020). My second goal was to use the same alternative sampling methods to examine Brook Trout-habitat associations at three spatial scales and to determine whether the habitat associations are unique to one spatial scale or common among spatial scales. The three spatial scales examined were the segment (>200m), reach (50m) and microhabitat (1m2 ) scale. Environmental DNA concentrations and UWVC surveys showed a strong agreement with Brook Trout presence/absence (89% and 78%, respectively) and estimated abundance but significant interannual variation existed for both methods between sampling years. Habitat associations determined that Brook Trout are associated with both scale-specific habitat characteristics (i.e., canopy cover at the reach scale, baseflow index at the segment scale) but were also strongly associated with common habitat characteristics (i.e., surface temperature, stream width, watershed size (km2 ) and discharge). The results of this study support the use of eDNA and UWVC as alternative methods to electrofishing for determining the presence/absence of Brook Trout and abundance. These results also suggest that both scale-specific habitat variables and habitat variables measured across scales are important factors for Brook Trout abundance and highlights what key habitat characteristics fisheries managers should prioritize for management.