Effects of fish on the local abundance of crayfish in stream pools

A survey of fish and crayfish distributions in pools in small Kentucky streams suggested that predatory fish have strong effects on the local distribution of cray fish. I tested this hypothesis by experimentally manipulating the density of fish in stream pools. The predator, green sunfish (Lepomis cyanellus), strongly reduced the density of crayfish (Cambarus bartoni). prey movement rates into and out of pools were low compared to estimated predation rates: consequently, I concluded that observed reductions of crayfish densities by fish predators were due mainly to direct consumption. Estimated rates of predation and prey movements were combined into a model to simulate observed predator impact on crayfish in patches larger and smaller than the scale of the experiment. The simulation suggested that the results were robust to increases in spatial scale. Data From the survey showed that crayfish densities in fish pools and Fishless pools only differed for pools deeper than approximately 30-50 cm, probably because shallow pools had fewer and smaller fish. Thus, shallow pools provide a refuge for crayfish against fish. Very shallow pools (10-20 cm) generally had low densities of crayfish. Possible mechanisms that could explain the low density of crayfish in shallow pools include stronger effects of floods and higher predation pressure from terrestrial predators in these pools.