Tuesday, May 27, 2008
232

Effects of trout invasions on benthic assemblages

Kurt D. Fausch1, Fabio Lepori1, Joseph R. Benjamin2, and Colden V. Baxter2. (1) Department of Fish, Wildlife, and Conservation Biology, Colorado State University, 1474 Campus Delivery, Fort Collins, CO 80523-1474, (2) Stream Ecology Center, Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007

Although introductions of salmonids in fishless streams are likely to affect prey assemblages, the effects of the replacement of native by non-native trout remain poorly understood. Brook trout, originally from eastern U.S. and Canada, are replacing native cutthroat trout in streams across the western U.S. We assessed the consequences for benthic invertebrates, which include a large portion of the prey of both trout species. We predicted that brook trout would consume more invertebrates overall because of higher population densities and greater propensity for benthic feeding. In the short term, however, the impact of trout on invertebrate populations might reflect not only consumption, but also emigration (which might increase or decrease) and release from larger invertebrate predators, which are consumed by trout. To address these mechanisms and measure the size of these effects, we conducted a large-scale field experiment in Idaho, fencing reaches along a headwater stream to establish treatments consisting of cutthroat trout, brook trout at two densities (natural and matching the density of cutthroat trout), or no trout. Here we report the main results and discuss implications for management.


Web Page: experiment, drift, non-native trout, predation, Western streams

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