Influence of Extreme Temperatures on Consumption and Condition of Walleyes in Pymatuning Sanctuary, Pennsylvania

Abstract

Temperature is an important abiotic factor affecting fish population dynamics. An unfavorable thermal regimen can restrict a species' ability to thrive in its environment. We studied the effects of an unfavorable thermal regimen on the feeding, condition, and growth of an unexploited population of walleyes Stizostedion vitreum in Pymatuning Sanctuary, Pennsylvania. We used gastric lavage to sample stomach contents of walleyes captured by electrofishing during bimonthly sampling from May through October, 1997–1998. We sampled available forage by shoreline seining and recorded water temperatures using an electronic temperature monitor. To determine the effects of temperature on walleye feeding, condition, and growth, we examined relationships among water temperature, forage availability, percentage of stomachs containing food, food consumption by number and volume, and relative weight of adults. Average daily temperature and daily minimum temperature were above the thermal optimum (22°C) for most of the summer in both years. Adult catch-per-unit-effort, percentage of stomachs containing food, average number of food items, and volume of food consumed were all lowest during summer. Average relative weight of adults was lowest during the warmest periods of summer, and was negatively related to average temperature, as was average volume of food consumed. The thermal regimen in Pymatuning Sanctuary negatively affected adult walleye feeding activity, consumption, and condition, and was thus an important factor in structuring this population.