Calibration / Validation of AFS North American Standard Gillnetting for Walleye, Lake Trout and Brook Trout

Ontario’s Broad-scale Monitoring (BsM) program has adopted the North American gillnet standard (Bonar et al. 2009) for sampling fish communities. One objective of the BsM program is to assess the status of fish species across the Province. Ontario is developing diagnostic tools to assess the status of walleye, lake trout, and brook trout that rely on individual lake measures biomass, rather than relative abundance (catch per unit effort (CPUE)). To enable the translation of gillnet CPUEs to estimates of abundance, Ontario has designed a large scale study to measure the catchability (i.e., relationship between CPUE and biomass) of the NA gillnet standard for these three species. The study design acknowledges various factors that may influence catchability (e.g. time of sampling, climate, body size), stressing the need for a large study. Proposed methods include mark-recapture methods to estimate fish density/biomass paired with multiple NA gillnet surveys throughout the sampling season to estimate CPUE. Preliminary results indicate that adult walleye CPUE is well correlated with adult biomass with a catchability coefficient of approximately 0.5. Study of the catchability of NA gillnets for walleye, lake trout and brook trout in climates warmer and colder than available in Ontario calls for more collaborative inter-agency research. Ontario has developed a partnership with Quebec and is initiating partnerships with other agencies for this purpose.