Factors Limiting Brook Trout Biomass in Northeastern Vermont Streams

Abstract

AbstractHabitat, water chemistry, and water temperature requirements and preferences have been well documented for stream‐dwelling Brook Trout Salvelinus fontinalis, but fisheries managers rarely know what factors limit Brook Trout abundance in their jurisdictions. We measured various habitat (width, depth,% pool, and wood abundance), water chemistry (pH and conductivity), and water temperature metrics and estimated Brook Trout biomass at 33 stream reaches in northeastern Vermont to determine what factors were most strongly related to Brook Trout biomass, with the ultimate goal of predicting whether adding wood to these streams could be expected to increase Brook Trout abundance. We fit generalized additive models to investigate potential linear and nonlinear relationships between Brook Trout biomass and the various habitat, chemistry, and temperature metrics. Akaike's information criterion was used to rank candidate models. The top‐ranked model included the duration of water temperatures exceeding 20°C, total wood density, and maximum riffle depth, and it predicted that Brook Trout biomass could be expected to increase with increasing woody habitat as long as water temperature does not exceed 20°C for 200 h or more per summer. The model also predicted that the benefits of adding woody habitat would be more pronounced in streams with deeper riffles. The absence of stream pH and pool area from the top‐ranked models was surprising. Our results highlight the importance of evaluating the local relationships between fish biomass and stream habitat as well as the important influence of study design on the results and conclusions.Received August 10, 2012; accepted October 23, 2012