Long-term tagging reveals variable escapement of stocked Muskellunge among four Ohio reservoirs: Consequences for managing reservoir fisheries

Abstract

Muskellunge Esox masquinongy are stocked by the Ohio Department of Natural Resources, Division of Wildlife (ODNR-DOW) into nine reservoirs to create trophy fisheries. Escapement is recognized as a potential impediment to maintaining quality fisheries in these reservoirs. We evaluated the escapement of Muskellunge at four reservoirs using mark-recapture methods during 2013–2022. At each reservoir, all juvenile Muskellunge (254–305 mm) stocked during 2013–2018 were implanted with passive-integrated-transponder (PIT) tags prior to release. In addition, adult mark-recapture sampling events were conducted by the ODNR-DOW during 2019–2022 to check for tagged fish and implant untagged fish. Muskellunge anglers were also outfitted with handheld PIT readers to scan and report tagged fish during the study. Escapement was monitored continuously with PIT tag detection systems installed within dam spillways. We used multi-state (in-reservoir vs escaped) mark-recapture models to estimate annual escapement for juvenile (≤ age 1) and adult Muskellunge. A total of 51,826 fish were tagged (51,052 juveniles, 774 adults), resulting in 3428 detections (2316 individuals). The number of Muskellunge escaping varied widely among reservoirs (0–481). Most escapement (85 %) occurred during the spring (March–May). Nearly all (96 %) known age fish that escaped were age 3 or greater. Modelling revealed that annual probability of juvenile escapement (≤ 0.02) was likely inconsequential at all reservoirs. However, adult escapement was highly variable among reservoirs (mean = 0–0.34). Escapement was lowest at reservoirs where water levels are managed via offshore sluice-gate tower structures, and greatest at locations where surface water is discharged from along-shore structures (i.e., crest gates and unregulated spillway). Where escapement occurred, there was a negative relationship between the annual probability of escapement and fishing success. Results will be useful for informing stocking strategies, mitigating fish loss, and managing fishery expectations.