Bull Trout Detection Probabilities

Development of Interim Tools for Predicting Bull Trout Detection Probabilities

The development of efficient and effective fish management depends, in part, upon the ability to accurately depict the combinations of factors (e.g., habitat, water temperature) that affect fish distribution. These in turn, require adequate sampling effort to ensure high quality data for analyses and model building. However, bull trout (Salvelinus confluentus), a Federally listed species, are relatively rare and difficult to sample; hence sampling protocols that fail account for low sampling efficiency and low population abundances may fail to detect bull trout when they are present. There remains a critical need to develop tools that allow fishery biologists to accurately estimate bull trout detection probabilities and develop sampling protocols that ensure high quality data.

CONCLUSIONS

The sampling efficiency of day snorkeling was positively related to water temperature and visibility and negatively related to stream gradient and density of large wood.
Night snorkeling sampling efficiencies were positively related to stream gradient, water temperature and visibility and negatively related to wood density.
Three-pass backpack electrofishing efficiency was negatively related to mean stream width, depth, gradient, and large wood density.
Sampling efficiency was, on average, greatest for 3-pass electrofishing (26.4%) and lowest for day snorkeling (10.2%). Night snorkeling efficiencies averaged 24.8% across habitat types.
Three-pass electrofishing and single-pass night snorkeling were the most effective techniques for detecting bull trout and required, on average, 24 and 25 samples, respectively to detect bull trout with 80% power.