Evaluation of Artificial Barriers in Small Rocky Mountain Streams for Preventing the Upstream Movement of Brook Trout

Abstract

Artificial barriers are important management tools for protecting populations of native fishes from encroaching nonnative species. We evaluated the effectiveness of gabion and culvert barriers in preventing upstream movement of brook trout Salvelinus fontinalis in four small Rocky Mountain streams that contained native populations of Colorado River cutthroat trout Oncorhynchus clarki pleuriticus. A rock-filled gabion in one stream and a road culvert in a second stream appeared to block upstream movement of brook trout; no fish marked and released downstream of the barriers were subsequently found upstream of the barriers. However, in a third stream, 18 of 86 brook trout marked and placed downstream of a rock-filled gabion barrier were later found upstream of the barrier during 3 years of evaluation. These fish ranged in length from 81 to 224 mm total length, so all size-classes were able to navigate past the structure. One brook trout moved upstream past the gabion twice, the second time during low flows when all water was percolating through the structure. We concluded that brook trout were able to move upstream through the rocks in this gabion barrier because fine sediments had not filled in all the interstitial spaces. Attention should be given to preventing movement of fish through gabion-type barriers, not just over or around them. In the fourth stream, 1 of 48 marked brook trout was found upstream from a road culvert barrier. Because this barrier appeared to be functioning properly during our study, we suspect this fish was moved upstream by an angler.