Influence of Substrate Composition and Suspended Sediment on Insect Predation by the Torrent Sculpin, Cottus rhotheus

Abstract

Studies conducted in laboratory streams showed that torrent sculpins (Cottus rhotheus) congregated in regions of limited cover when exposed to a sand substrate. When cobbles were added, their distribution was more uniform. Various combinations of sand, pebbles, and cobbles significantly influenced sculpin predation on the stonefly Hesperoperla pacifica, the mayfly Ephemerella grandis, and the caddisfly Rhyacophila vaccua. During 24-h tests, each species experienced 95–100% predation when tested on sand substrates. When different combinations of cobbles and pebbles were added, predation was appreciably reduced. Sculpin predation on H. pacifica, Hydropsyche sp., and Heptagenia solitaria was influenced more by substrate than suspended sediments when substrate and suspended sediment (0–1250 mg∙L−1) were tested interactively. Predator avoidance tactics differed among prey species as changes were made in the physical characteristics of the environment.Key words: predator–prey, sculpin, insects, suspended sediment, substrate, turbidity, behavior