The effects of invasive brook trout removal on native Colorado River cutthroat trout in a small headwater stream in Northeastern Utah


Category:  Fisheries
Linked Publication
Language: English
Author(s): Garn J. Birchell
Description: We evaluated the response of Colorado River cutthroat trout to brook trout removal from a small headwater stream in Northeastern Utah. Brook trout were removed via depletion-removal electrofishing and gillnets. Nine removal passes were completed between 2003 and 2005. We estimate that the four pass efforts resulted in the removal of less than 70% of the brook trout population each year. Therefore, complete eradication was not achieved, so periodic removal of brook trout will be needed to maintain the cutthroat population in Reader Creek. Statistically significant increases in relative weight (Wr) values for cutthroat trout were observed. Relative weight values for all size groups of brook trout increased significantly between pre and post removal periods. Captures of age-1 cutthroat trout increased from 31 fish in 2003 to 146 fish in 2004. This number increased further to in 2005. Cutthroat trout were stocked in the fall of 2004 and we could not differentiate between stocked and naturally reproduced fish. Adult fish from upstream stations had moved into middle and lower stream stations, while age-1 fish expanded from downstream stations into middle stations. We captured cutthroat trout that exhibited site fidelity, mobility, and a combination of the two behaviors. Cutthroat trout shifted from selecting species in the order Tricoptera in 2003 to species in the order Plecoptera in 2004. During both years we examined diet, Diptera species selected. Because of the difficulty achieving complete brook trout eradication in streams similar in size to Reader Creek, we do not recommend mechanical removal for instances where complete eradication of brook trout is the goal. If complete eradication is not the goal or if circumstances dictate depletion removal electrofishing is the only alternative, depletion removal may be useful for maintaining low abundances of brook trout. In cases where depletion removal electrofishing is going to be used to control brook trout numbers, a priori project planning should address maximizing capture efficiency and minimizing bias in population abundance estimation.