Abiotic and biotic factors associated with brook trout invasiveness into bull trout streams of the Canadian Rockies

An information-theoretic approach was used to determine the association between brook trout (Salvelinus fontinalis) invasiveness and a suite of abiotic and biotic factors, measured at 80 sites from 51 streams in the Canadian Rockies. The streams selected had confirmed brook trout invasions and were identified as current or historical nursery habitat for native bull trout (Salvelinus confluentus). The biomass at most sites was strongly or completely dominated (95%–100%) by one species or the other, and sites were classified as having high brook trout invasiveness (>60% of the biomass of the community relative to remnant bull trout) or low invasiveness (<40%). Among abiotic factors, high brook trout invasiveness was positively associated with stream temperature and undercut bank habitat, but negatively associated with large in-stream substrate (cobbles and boulders). Among biotic factors, brook trout invasiveness was negatively associated with co-occurring rainbow trout (Oncorhynchus mykiss) or brown trout (Salmo trutta), two other introduced species. Brook trout appear to dominate communities over native bull trout where thermal or habitat niche opportunities are provided for them, although other non-native species may restrict their invasion into bull trout streams.