Evaluating the relationship between mean catch per unit effort and abundance for littoral cyprinids in small boreal shield lakes

Catch per unit effort (CPUE) is commonly used as a relative measure of littoral fish abundance; however, few studies have examined this relationship for boreal shield lakes. We used non-linear regression to generate relationships between mark-recapture abundance estimates and mean CPUE derived from 7 years of standardized fishing using baited minnow traps for two common cyprinid species; pearl dace (Margariscus margarita) and fathead minnows (Pimephales promelas), in littoral areas of two small boreal lakes. We produced significant, positive CPUE-abundance relationships for pearl dace and fathead minnows. Pearl dace were less variable in daily CPUE during the course of the study, suggesting they may require less sampling effort than fathead minnows to precisely estimate their population size. Density estimates derived from our estimates of abundance were consistent with those from similar boreal shield lakes, providing confidence in our method to estimate abundance. Finally, we developed relationships to estimate population size from long-term monitoring data collected on these same cyprinid species using two types of small mesh trap nets. Non-linear relationships were developed between mean trap net CPUE and abundance estimates derived from minnow traps for fathead minnows, but not pearl dace. These relationships should permit population estimates from mean CPUE data collected using similar capture methods in similar lakes.