A Native Westslope Cutthroat Trout Population Responds Positively after Brook Trout Removal and Habitat Restoration

Abstract

The distribution and abundance of wests lope cutthroat trout ( Oncorhynchus clarki lewisi; WCT) have dramatically declined across much of their historical range, but particularly within the upper Missouri River basin of Montana. A genetically pure remnant WCT population inhabits White's Creek in the Missouri River basin, Montana; however, this population was extremely low during the early 1990s (~ 80 fish ≥ 75 mm long) due primarily to interaction with sympatric, nonnative brook trout (Salve/inus fontinalis) and habitat alterations caused by past dredge and placer mining. From 1993 to 2000 brook trout were removed by repeated electrofishing. In 1995 the mining-impacted portion of the stream was restored and a fish migration barrier was constructed. Brook trout were successfully removed from White's Creek above the constructed barrier after eight years of intensive electrofishing effort. The population of WCT increased dramatically, at least seven-fold, following removal of brook trout, with the most pronounced response seen for age-0 WCT. The portion of White's Creek where stream habitat was restored supported similar abundances ofWCT (catches of ~30 WCT ≥ 75 mm long/100 m of stream) as found in natural stream reaches above and below this restored portion. Following brook trout removal, standing crops of WCT in allopatry were similar to combined standing crops of brook trout and WCT in sympatry prior to initiation of brook trout removal. Electrofishing appeared to be an effective tool for removal of brook trout in this small stream with relatively uncomplex habitat; however, we caution that it may not be effective in larger systems.