Influence of Extreme Temperature and Flow Events on Brook Trout Recruitment

Extreme flows and temperatures can have major impacts on fish populations and are predicted to become more common with future climate change. Accurately predicting population responses to such events depends on appropriately accounting for them in population models. Trout recruitment is an important determinant of population dynamics and young individuals are likely to be particularly sensitive to environmental fluctuations. We sought to determine the effects of floods, droughts, and summer temperature extremes on brook trout (Salvelinus fontinalis) recruitment using 13 years of data from four streams within a single watershed. We used a Bayesian hierarchical model to estimate fall YOY abundance while accounting for capture probability and allowing covariate parameters to vary among streams. The model included environmental covariates hypothesized to influence recruitment as well as spawner abundance. Fall YOY abundance fluctuated nearly an order of magnitude among years and was more closely related to environmental variability than spawner abundance; however, abundance responded differently to temperature and flow in different streams. Our results highlight the importance of interactions between habitat conditions and environmental variability and the challenge of generalizing such mechanistic predictions across streams.