Evaluation of artificial barriers in small rocky mountain streams for preventing the upstream movement of brook trout

Artificial barriers are important management tools for protecting populations of nativefishes from encroaching nonnative species. We evaluated the effectiveness of gabion and culvertbarriers in preventing upstream movement of brook trout (Salvelinus fontinalis) in four smallRocky 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 asecond stream appeared to block upstream movement of brook trout; no fish marked andreleased 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 gabionbarrier were later found upstream of the barrier during 3 years of evaluation. These fish ranged inlength from 81 to 224 mm total length, so all size-classes were able to navigate past thestructure. One brook trout moved upstream past the gabion twice, the second time during lowflows when all water was percolating through the structure. We concluded that brook trout wereable to move upstream through the rocks in this gabion barrier because fine sediments had notfilled in all the interstitial spaces. Attention should be given to preventing movement of fishthrough gabion-type barriers, not just over or around them. In the fourth stream, 1 of 48 markedbrook trout was found upstream from a road culvert barrier. Because this barrier appeared to befunctioning properly during our study, we suspect this fish was moved upstream by an angler