BAYeFISH

Understanding the population dynamics of juvenile salmon and trout within their freshwater habitats is crucial for the sustainable management of salmon and trout populations. In Sweden, monitoring of juvenile salmon and trout populations in freshwater relies largely on electrofishing, a non-lethal technique that uses an electric field to temporarily stun the fish, after which they can be netted, counted, and measured. Electrofishing can be performed as a single pass or through repeated passes at the same location. In the case of repeated passes, fish are successively removed during each pass and held in buckets until all passes are complete. The decline in catch between passes allows estimation of the total fish density; and the more passes performed, the more accurate the resulting density estimate.

A large proportion of the data in the Swedish electrofishing database (SERS) comes from single pass electrofishing, yet at many sites three or even four passes have been conducted. Using current data analysis methods, it is only possible to estimate fish density from sites with at least two passes, and single pass data are usually excluded from analyses.  BAYeFISH will develop statistical models for juvenile fish density estimation that use all the available data. It will also utilize environmental data (for example water temperature and flow) collected during electrofishing experiments, to improve predictions of catch rates.

Detecting whether a fish population is stable, increasing, or decreasing is an important aspect of monitoring programs, yet the feasibility of doing so depends on the quality of the available data. BAYeFISH will investigate whether the current electrofishing monitoring program allows robust trend detection, and provide new insights about the experimental design of electrofishing monitoring (e.g. number of sampling sites and the number of fishing passes at each site) to allow detection of changes in population size over time.