PROCEDURAL EFFECTS OF PREY TETHERING EXPERIMENTS - PREDATION OF JUVENILE SCALLOPS BY CRABS AND SEA STARS

This study examines the effects of an experimental tethering procedure often used in field predation experiments. In laboratory experiments, juvenile sea scallops Placopecten magellanicus, either free or tether ed, were offered to predatory crabs Cancer irroratus and sea stars Ast erias vulgaris. The effect of the tethering procedure on predation rat es was specific to a predator-prey interaction and could be predicted based on an understanding of the underlying behavioural mechanisms. In crab-scallop interactions, encounter rate was a major determinant of predation rate. Since tethering did not affect encounter rates, it did not significantly affect predation rates by crabs. In contrast, in se a star-scallop interactions, the probability of sea stars capturing en countered scallops was a major determinant of predation rate. Tetherin g limited the scallops' escape response, which increased the probabili ty of capture and, hence, predation rate. Therefore, assessment of the relative importance of these 2 predators in determining scallop survi val in field experiments would be biased by the differential effects o f the tethering procedure.