Temperature-Dependent Maximum Daily Consumption of Juvenile Salmonids by Northern Squawfish (Ptychocheilus oregonensis) from the Columbia River
Maximum daily consumption rate (Cmax as ration or number) of northern squawfish (Ptychocheilus oregonensis) from the Columbia River increased exponentially as a function of temperature. Predator weight did not explain a significant independent proportion of variation in Cmax. The mean maximum daily ration, determined from replicate ad libitum feeding on juvenile Pacific salmon (Oncorhynchus spp.), was 0.47, 0.70, 3.39, and 4.50 cg∙g−1 at 8.0, 12.5, 17.0, and 21.5 °C, respectively. The corresponding mean daily number eaten was 0.50, 1.17, 4.25, and 7.01 prey per predator at the four increasing temperatures. To quantify the temperature-dependent consumption relation, replicate Cmax data within the preferred temperature range were fitted to exponential and exponential sigmoid models. On the basis of a knowledge of thermal relations of northern squawfish, we combined hypothetical Cmax data at temperature extremes with our mean experimental results to fit an algorithm suitable for use in simulation modeling. Both the generalized gamma and biological-rate (Thornton and Lessem. 1978. Trans. Am. Fish. Soc. 107: 284–287) algorithms were suitable to describe a hypothetical temperature–Cmax model over the entire environmental temperature range of 0–27 °C observed in the Columbia River.