Evaluating Muskellunge catch-and-release mortality at elevated summer water temperature

Abstract

Listen

Translate article

Abstract Objective Fisheries managers and anglers have expressed concerns regarding warmwater angling mortality, representing a need to evaluate mortality rates at various water temperatures and multiple latitudes. Up to 97% of Muskellunge Esox masquinongy caught by anglers are released, and previous research on catch and release (C&R) for Muskellunge has suggested relatively low mortality rates (0–5%). However, those studies were all conducted within the range of water temperatures that are thermally optimal for Muskellunge and generally at water temperatures less than 25°C. As many Muskellunge populations routinely experience temperatures greater than 25°C during the summer months our objective was to quantify warmwater (>25°C) C&R mortality rates in Muskellunge. Methods We collected 102 adult Muskellunge (>760 mm) and stocked them into and identify factors influencing mortality by using experimental ponds. Adult Muskellunge (n = 102) were stocked into eight earthen or plastic-lined flow-through ponds (0.06–0.71 ha) at densities less than 16 fish/ha. Muskellunge (n = 50) were angled by utilizing specialized Muskellunge fishing gear at water temperatures of 19.6–32.6°C, with 32 fish being caught at temperatures exceeding 25°C. After being angled, fish were closely monitored for 2 weeks to assess mortality; fish that remained uncaught during the experiment were used as controls (n = 53). Result Mortality was greater for angled fish (30.0%) than for control fish (11.3%). Differences in C&R mortality were compared across a range of temperature regimes using Firth logistic regression. Five-day cumulative temperature and net time were positively related to the probability of mortality, but size and sex were unrelated to mortality. Increasing C&R mortality with temperature was mitigated somewhat by lower catch rates at higher temperatures. Mortalities per 100 angler-hours were 0 at <25°C, 4.98 at 25.00–27.49°C, 2.48 at 27.5–30.0°C, and 1.17 at >30°C. Conclusion Recent field studies have identified the importance of thermal refuge in mitigating summer C&R mortality of Muskellunge. This study identified specific temperature conditions responsible for elevated mortality in the absence of refugia. Although increasing temperatures above 25°C led to increasing C&R mortality in our ponds, lower catchability seemingly provided some mitigation. The interactive effects of thermal refugia and catch rates with temperature warrant further investigations into population-level effects at varying levels of exploitation.