The influence of temperature and habitat on the distribution of chiselmouth, Acrocheilus alutaceus, in British Columbia

Synopsis We intensively sampled fish in rivers and streams within a single major drainage basin (the Blackwater River) and across major drainages in British Columbia to assess the factors influencing distribution of chiselmouth, Acrocheilus alutaceus, and to develop models for predicting chislemouth presence. Chiselmouth were typically absent from sites with maximum temperatures below 20 • C or 2100 annual degree days, both within a single drainage and between larger drainages. Indices of stream size (bankfull channel width and basin area) were the most significant predictors of chiselmouth presence within the Blackwater drainage (p = 0.016 and p = 0.032, respectively), and inclusion of thermal variables only marginally increased classification success. In contrast, bankfull channel width and basin area were poor predictors of chiselmouth presence in mainstem habitat within larger drainage basins throughout British Columbia. Inclusion of thermal variables (particularly degree days > 12 • C) doubled correct classification rates of chiselmouth presence across larger drainage basins. These habitat associations suggest that water temperature is the primary constraint on presence of chiselmouth populations in larger drainages across a landscape, while selection of different habitat types (mainstem habitat over smaller tributaries) determines distribution within any given basin

Effects of catchability variation on performance of depletion estimators: application to an adaptive management experiment

Depletion methods use sequential catches to estimate abundance, and commonly assume constant capture probability. Violation of this assumption results in abundance estimates that are biased low, and confidence bounds that indicate unwarranted precision. I used simulation to compare performance of three alternative estimators that explicitly consider catchability change over passes. If catchability declined, non-constant catchability models failed to reduce bias, but better characterised uncertainty. I used non-parametric methods to examine time and treatment effects on the precision and bias of abundance estimates from depletion data for a large management experiment on the Bridge River, BC. Catchability increased over time, suggesting a concurrent change in bias. The magnitude of the change in bias was a function of the decline in catchability within depletion experiments. Because estimates of the decline in catchability were uncertain, it was difficult to assess the magnitude of change in bias