The Study
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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 assumed to 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=103) 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 (11.1%). 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 fight time, hooking location, size, or gender 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.
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Collection Location and Size
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Muskellunge were collected from the following sites and stocked into their corresponding hatchery facilities operated by federal and state management organizations. A total of 103 Muskellunge were included in the study ranging from 761mm to 1208mm in length. A total of 50 Muskellunge were caught and released while 53 remained uncaught and acted as controls. We experienced catch-and-release mortality rates of 30% and control mortality rates of 11.1%.
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Results: Temperature and CPUE
Fitted Firth logistic regression (top) and linear regression models (bottom) showing the relationships between average daily temperature (°C) and probability of catching a Muskellunge and average daily temperature and angler CPUE. Data collected from n=78 trips conducted in 2020 and 2021. Shaded regions represent ±95% CI.
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Average daily temperature during acclimation and angling periods of all ponds utilized for the Muskellunge mortality study. MD = Maryland pond 7, NC 16 = North Carolina pond 16, NC 17 = North Carolina pond 17, VA = Virginia pond 9, WV 5 = West Virginia pond 5, WV 6 = West Virginia pond 6, WV P = West Virginia (2020) pond, WI S = Wisconsin surface temp., and WI B = Wisconsin bottom temp.
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Results: Probablity of Mortality
We found that probablity of catch-and-release mortality was best described through the additive relationship between 5-day cumulative temperature and net time. Both variables were positively correlated with probablity of mortality in angled fish. 5-day cumulative temperatures is described as the cumulative total of average daily temperatures over a 5 day period in which catch time is the midpoint of the 5 day period. This enables us to understand the effects of temperature on mortality before and after an angling event. Net time was described as the amount of seconds the fish spend in the net. The relationship between temperature at time of catch and net time followed a similar trend but was not the best performing model. However this model offers more relevant information to anglers. For example when net time was held at 60 seconds mortality rates were 0.73% at catch temperatures of 22°C, 1.95% at 24°C, 5.27% at 26°C, 14.19% at 28°C, and 38.23% at 30°C.
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Fitted model utilizing Firth logistic regression showing the effects that five-day cumulative temperature has on probability of mortality when net time is held constant (Top left),the effects of net time when five-day cumulative temperature is held constant (Bottom left), effects of temperature at time of catch when net time is held constant (Top right), and the effects of net time when temperature at time of catch is held constant (Bottom right). Shaded regions represent ±95% CI.
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Conclusions
We utilized hatchery ponds as mesocosms to monitor post C&R mortality of Muskellunge for up to 4 months. We noted total mortality rates of 20.4% and C&R mortality rates of 30%. We demonstrated increasing rates of C&R mortality with increasing temperatures for Muskellunge, perhaps confirming the caution put forth by Hayob (2013) and other anglers who cease fishing at temperatures >26.7°C. We discovered that mortality is strongly associated with the five-day cumulative total temperature, suggesting that the temperatures fish experience prior to and after the angling event can affect probability of mortality. Additionally, we found that time spent in the net can also influence odds of mortality for caught-and-released fish. Our results suggest that water bodies that have significant thermal refuge or do not approach temperatures >25°C would experience lower summer C&R mortality than our ponds. This information can aid conservation-oriented anglers in determining when Muskellunge C&R mortality may limit their conservation goals. We encourage future studies to validate these results and to continue research on the possible consequences to Muskellunge populations this poses.