(English) Electrofishing catchability of age-0 muskellunge in northern Wisconsin lakes

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To assess the effectiveness of muskellunge (Esox masquinongy) stocking, biologists conduct electrofishing survey in fall to estimate catch per effort (CPE) and relative contribution of stocked fish. Inherent assumptions of this sampling are that wild and stocked fish have equal probability of capture and that changes in CPE reflect differences in actual abundance. However, capture rates of age-0 muskellunge tend to be low for both wild and stocked fish making it difficult to determine if electrofishing catch is a meaningful predictor of actual abundance. The goal of our study was to determine the efffectiveness of electrofishing for capturing individual age-0 muskellunge by determining locations of stocked fish released into two lakes in northern Wisconsin. All stocked fish received a fin clip and at least 40 fish per lake were inserted with radio transmitters. All fish were released at a single boat ramp on each lake which followed standard Wisconsin Department of Natural Resources (DNR) protocols. Stocked muskellunge with transmitters were tracked weekly for one month after release. Fish were also sampled weekly using standard Wisconsin DNR electrofishing methods that included a single boat following a single line transect around the shoreline of each lake. Comparing known locations of radio-tagged fish to the area sampled by the electrofishing boat revealed that most sampling effort was expended outside the area where stocked fish were located. Our initial results suggest that the majority of hatchery fish remained in the vicinity of the release location with fish moving a maximum distance of 0.4-0.7 km on average away from the release location within four weeks after stocking. Based on these results, biologist will be able to improve sampling protocols to evaluate muskellunge stocking success by stratifying sampling effort so more time is spend sampling where fish are located.