The mechanics of the predation of the sculpin, Cottus beldingi, was examined in artificial laboratory stream conditions using three different prey types; Gammarus lacustris, Arcynopteryx californicus, and Ephemerella (drunella). It was found that encounter probability and capture success were most important in determining the observed prey selectivity. In feeding trials in which all three prey species were present selectivity was highest for Gammarus and lowest for Ephemerella. This reflects the observed differences in the activity levels of these species.
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