Effects of Temperature and Density on Consumption of Trout Eggs by Orconectes propinquus and O. rusticus

Using laboratory experiments, we assessed the effect of temperature and predator density on consumption of trout eggs by crayfish. We quantified the effect of four temperature ranges (2-3, 4-5, 7-8, and 10-12°C) on consumption of lake trout (Salvelinus namaycush) and rainbow trout (Oncorhynchus mykiss) eggs by a native (Orconectes propinquus) and an exotic (Orconectes rusticus) crayfish found in the Great Lakes. Mean individual consumption ranged from 0.1 to 1.5 lake trout eggs per day and from 1.0 to 5.5 rainbow trout eggs per day, respectively. Temperature influenced consumption for O. rusticus feeding on rainbow trout eggs but not O. propinquus. The effect of conspecific predator competition on rainbow trout egg consumption was evaluated using three densities of crayfish (1, 5, 10 per tank). For O. rusticus, mean individual consumption rate was higher at the lowest crayfish density (1 crayfish/tank) than at medium (5 crayfish/tank) or high (10 crayfish/tank) densities. A similar conspecific effect was not evident in O. propinquus and total consumption per unit area increased with crayfish density. The effect of competition among crayfish species on consumption of rainbow trout eggs was examined by comparing feeding rates at high crayfish abundance levels in single and mixed species treatments. Mixed species interactions did not significantly alter crayfish feeding rates. Results from these experiments provide empirical data to aid in modeling how temperature and predator density affect lake trout egg predation rates in the field.