Summer Habitat Use, Home Range, and Effect of Catch and Release Mortality on the Trophy Potential of Muskellunge, (Esox masquinongy, Mitchill, 1824), in a Southern Reservoir Population

Research on Muskellunge (Esox masquinongy, Mitchill, 1824) catch-and-release mortality has been historically focused on the Midwest, Great Lakes, and Ontario. In the southern portion of their range, which we consider to be the portion of the species distribution south of the Mason-Dixon Line (~40°N), Muskellunge, may experience significantly warmer temperatures than those in previous studies and anglers have expressed concern about summer catch-and-release mortality. As part of a broader study to quantify catch-and-release summer mortality in the southern range of Muskellunge, we utilized radio telemetry and active tracking to verify individual movement and survival of Muskellunge in Stonewall Jackson Lake, WV. The lake has a 52-inch minimum size limit for Muskellunge, making it effectively catch-and-release except for trophy-sized individuals. We tagged 45 Muskellunge in the spring of 2020 and 47 Muskellunge in the spring of 2021 with radio telemetry transmitters, PIT tags, and an external dart tag for unique identification by anglers. Muskellunge were tracked weekly from June through September and monthly in October, November, March, April, and May. GPS location and water quality parameters were taken at each unique location. We collaborated closely with anglers and Muskies, Inc. to promote cooperation in the study and to provide rewards to anglers catching and reporting tagged fish. Our estimate of angling mortality was based on survival of individuals reported caught by anglers versus survival of fish not reported caught-and-released. In 2020, 10 fish were caught by anglers when the temperatures exceeded 25o C, and mortality was 10 percent. In 2021, 19 fish were caught by anglers when temperatures exceeded 25o C, mortality was 10.5 percent. Twenty-six fish were caught during Spring, Fall, and Winter, and survival was 100%. Individual growth model simulations were used to estimate the effect that catch and release mortality has on trophy potential under different levels of mortality and summer exploitation. Small differences, \u3c 2 % difference in the proportion of the population reaching memorably size, were seen at what we estimate are current values of summer catch and release mortality (Cm = 0.1) and summer exploitation (Se = 0.15). Effects are more pronounced at higher levels of catch and release mortality and exploitation (Se = 0.19; Cm = 0.3). A closed summer season doubles the number of trophy individuals from 20 to 40 individuals (2 and 4% of the 1000 age-1 individuals). Muskellunge oxy-thermal habitat use, home range, and movement was identified from radio telemetry locations. Summer surface water temperatures where Muskellunge were located averaged 27.5 ± 0.17 °C in 2020 and 26.5 ± 0.74 °C in 2021, with maximum surface water temperatures for Muskellunge location reaching 32.5 ° C. However, Muskellunge were able to access thermal refugia near the thermocline and had an average transmitter temperature of 23 ° C. Oxy-thermal refugia at tracking locations were calculated using TDO3, and the summer average was 17.3°C for the east side of the lake and 21.8°C for the west side. Muskellunge on the west side of the lake were utilizing water temperatures at or below the TDO3 levels during July and August based on their transmitter temperatures. In 2021 we used temperature-sensitive transmitters and documented summer thermal habitat use to be 23.1 ° C and observed dense clustering of Muskellunge in thermal refugia habitat. Thermal stress, which we measured with cumulative degree days (CDD) over 25 ° C, has been increasing steadily since 2003. The summer 95% minimum convex polygon (MCP) home range size averaged 30 ha in 2020 (SE=5.9) and 19 hectares (SE=2.9) in 2021. Muskellunge that were recaptured by anglers during the summer period had on average 16-hectare larger home range sizes than non-angled fish. Weekly distance moved did not differ significantly between seasons. Increased kernel density estimates of Muskellunge during the summer period are likely by driven by oxy-thermal refugia. This study provides managers with information on how the thermal regimes of a reservoir system impacts catch and release mortality, home range, and movement of Muskellunge