Stream restoration can keep invasive trout at bay

Posted on December 16, 2014

River restoration aims to build sustainable populations of native aquatic species by enhancing habitats and eliminating invasive species. However, because it can be difficult or impossible to remove exotic species once they’re established, stream managers often concentrate on assisting native species to coexist with invaders. So how successful is habitat enhancement as a way of promoting species coexistence? More information on this topic is needed, largely because post-restoration monitoring is often short-term, cursory or lacking altogether. Using snorkelling techniques, biologists sampled fish communities in artificial side channels of the Provo River in Utah, U.S.A., 2-4 and 9-10 years after the channels were constructed. Although local native fish species included suckers, sculpins, chub, dace and shiner, the fish assemblages in the main, channelized waterway and a short adjacent side channel were dominated by invasive trout (Salmo trutta). Native species were limited to large-bodied forms or those that could find a refuge in the substrate or in high-velocity areas avoided by trout. In contrast, fish communities in other side channels were significantly different from those in the main channel, apparently because of habitat differentiation and local isolation. In these side channels, trout were seldom seen: the presence of beaver dams restricted colonisation and the slow and stagnant water at the edges of beaver pools favoured native fish species. This case study shows that certain conditions created by river restoration can enhance native-exotic coexistence, but it was also clear that restoration work needs to be informed by a detailed knowledge of the habitat needs of the species concerned.

Reference: Billman, E.J. et al. 2013. Habitat enhancement and native fish conservation: can enhancement of channel complexity promote the coexistence of native and introduced fishes? Environmental Biology of Fishes 96, 555–566.