Impact of rip rap armoured shorelines on littoral zone fish habitat on the Winnipeg River, Canada

Abstract

This project sought to uncover the impact rip rap shoreline armouring may have on fish habitat. I assumed that fishes most likely to be affected by the physical alterations to the shoreline were those fishes associated with the shallow waters of the littoral zone. The study was limited to an examination of granite rip rap, used in a boreal river context, with application at a project scale. Over 43 000 small-bodied and juvenile large-bodied fishes were captured from the littoral zone along the Winnipeg River, MB along with measures of environmental variables. Information from these fishes and environmental variables was used to evaluate sites and site types, three different ways. Firstly, I used a two-pronged approach to evaluate sites, and simultaneously, to determine fish community health. Using PCA analysis, I found that Karr's Index of Biotic Integrity - IBI (1981) was highly correlated to species composition. I also found that Karr's IBI was able to uncover differences in shoreline habitat, even at a small scale (Long and walker, 2005). Higher IBI scores were associated with armoured sites. Secondly, I evaluated sites and site types using surrogate measures of production. Although production and species composition (especially abundance) may be collinear, they are not necessarily so. Although these measures are not fully independent of one another, they do provide important insights into habitat function. Notwithstanding, higher production values were associated with armoured sites. Lastly, I found that despite a priori differences in habitat at each sample site, a constrained analysis of the species composition information indicated that several environmental variables played a role in the quality of fish habitat. Among these variables, rip rap shoreline armouring was found to be associated with better quality habitat due to its causal effects on turbidity, among other things. The observational and multivariate nature of this study leads to specific conclusions about the ecological value of rip rap application. At the same time, these conclusions should be limited to boreal riverine systems until they have been examined for other systems.