Factors Limiting Brook Trout Biomass in Northeastern Vermont Streams

Abstract

Habitat, 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

ACKNOWLEDGMENTS

We thank the many people who helped collect data for this study. Vermont Fish and Wildlife staff members Pete Emerson, Kandis Barrett, and Ann Hare and Trout Unlimited staff members Joe Norton, Joe Martell, and Ben Matthews assisted with the collection of the fish and habitat data. Alkalinity titrations were performed by Jim Kellogg, Vermont Department of Environmental Conservation. John Magee, New Hampshire Fish and Game, developed the physical habitat assessment protocol that we used. Thanks to Tyler Wagner at the Pennsylvania Cooperative Fish and Wildlife Research Unit for invaluable statistical advice. Finally, thanks to two anonymous reviewers and the journal editors for helpful comments during the publication process. Funding for this study was provided by the Federal Aid in Sport Fish Restoration Act and Vermont fishing license sales.