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

Abstract

Angling for Muskellunge Esox masquinongy has become widespread and increasingly popular. Management strategies for Muskellunge include high minimum harvest lengths (>1016mm), closed seasons, and catch‐and‐release regulations. Due to these strategies and angler behaviors, up to 97% of Muskellunge caught are released, and anglers assume these fish survive to be caught again in the future. Previous research on catch‐and‐release mortality for Muskellunge has suggested relatively low mortality rates (0%‐5%). However, these studies were all conducted within the range of water temperatures that are thermally optimal for Muskellunge and generally at water temperatures <25°C. Muskellunge populations in some latitudes routinely experience temperatures >25°C during the summer months. Fisheries managers and anglers have expressed concerns regarding warm water angling mortality, representing a need to evaluate mortality rates at various water temperatures and multiple latitudes. Our objective was to quantify warm‐water (>25°C) catch‐and‐release mortality rates in Muskellunge (>760mm) and identify factors influencing mortality 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 of <16 fish/ha. Muskellunge (n=50) were angled utilizing specialized Muskellunge fishing gear at water temperatures of 19.6–32.6°C, with 32 fish being caught at temperatures >25°C. Fish were closely monitored for 2 weeks after being angled to assess mortality, and fish that remained uncaught during the experiment were used as controls (n=53). Mortality was greater for angled (30.0%) compared to control fish (11.3%). Differences in catch‐and‐release mortality were compared across a range of temperature regimes using firth's 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. Elevated catch‐and‐release mortality rates at warm water temperatures warrant investigations into the population level effects at varying levels of exploitation.

Spatial ecology and thermal preferences of muskellunge within a Midwest impoundment

“…This elevated activity rate may be a result of fish searching for suitable habitat, foraging on pelagic prey or from conspecific interactions, such as competition for homeranges/foraging locations, predation or mating. We also found that muskellunge are unable to locate thermal refuges in water cooler than 26°C, which can lead to higher incidental mortality following an angling experience (Booth et al., 2023). Managers of reservoirs should consider adding benthic structure or reducing stocking densities over time so prey can reduce in number (Bolding et al., 2004), and the effect of habitat addition on movement rates can be quantified in future studies.…”

“…Of concern, however, is how muskellunge use water temperatures 26°C and above in the summer. The 26°C temperature represents a critical threshold associated with higher incidental mortality following angling of muskellunge (Bauerlien, 2022; Beggs et al., 1980; Booth et al., 2023). This mortality is thought to be associated with greater physiological stress, which leads to reduced ability to recover and survive an angling experience (Booth et al., 2023).…”

“…The 26°C temperature represents a critical threshold associated with higher incidental mortality following angling of muskellunge (Bauerlien, 2022; Beggs et al., 1980; Booth et al., 2023). This mortality is thought to be associated with greater physiological stress, which leads to reduced ability to recover and survive an angling experience (Booth et al., 2023). Muskellunge in Shabbona Lake appear to be seeking ‘thermal refuges’ in the summer, defined as temperatures >2°C below surface temperature (Henesy et al., 2022; Torgersen et al., 2012), but, despite this use of thermal refuges, the temperature inhabited by fish exceeds 26°C in the summer.…”

“…For example, reservoir environments (impoundments) where muskellunge are frequently stocked are typically characterized with small size, chronic habitat loss and warm temperatures, all of which can create a challenging environment for sustaining muskellunge fisheries (Dombeck et al., 1984; Farrell et al., 2007; Kapuscinski et al., 2007; Younk, 1982). For example, muskellunge exposed to temperatures >26°C, which are common in some reservoir environments, has been documented to have higher levels of incidental mortality following angling (Booth et al., 2023), and work by Weber and Weber (2021) found increased mortality, and reduced activity, when water temperatures were above 25°C. Prior work has also found habitat heterogeneity and large home ranges to be critical in muskellunge management, and homogenous habitat coupled with small waterbodies can lead to greater energy expenditures and stress in muskellunge, increasing mortality (Eilers, 2008; Bergman et al., 2023; Landsman et al., 2015).…”