Comparing Time and Distance Effort in Electrofishing Catch Per Unit Effort

Electrofishing catch per unit effort (CPUE) is often used to index relative abundance of fishes.  Effort is typically recorded in units of either time or distance, such as catch per mile (CPM) or catch per hour (CPH).  Both time and distance effort have been correlated with population density of several fish species.  However, trends provided by each have been compared only once with limited scope and scale.  Our objective was to determine if time effort and distance effort provided similar indices for electrofishing CPUE for walleye Sander vitreus, largemouth bass Micropterus salmoides, and smallmouth bass Micropterus dolomieu in northern Wisconsin lakes.  Electrofishing was used to sample adult walleye, largemouth bass, and smallmouth bass on 311 lakes during 1995–2011.  Catch, time effort, and distance effort were recorded.  The relationship between CPH and CPM was strongly linear for all three species.  Because time effort and distance effort provide similar trends in CPUE, either may be used.  However, time effort may be more precise, easier to replicate, and has no chance of unit conversion error.  When using time effort, closely following established protocols is necessary to avoid introducing additional error.