Habitat use and movement by brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) in three tributaries of Nipigon Bay, Lake Superior

Abstract

Three streams were surveyed: Dublin Creek, MacInnes Creek, and Little Cypress River in Northwestern Ontario.

Knowledge of the physical habitat features of streams that are used by brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) is an essential component of insuring that the habitat is protected from potential impacts of land-use. In three small streams along the north shore of Lake Superior I examined the characteristics of the stream habitat and length of stream generally occupied by the brook trout and rainbow trout during the summer, including brook trout in the presence and absence of rainbow trout in the same stream. Electrofishing, passive integrated transponder (PIT) tagging, minnow trapping, two-way weirs, and habitat manipulations were techniques utilized in this study. Catch rates and fish biomass were examined in relation to associated characteristics of the stream habitat. The length of stream generally occupied was extrapolated from the capture locations of PIT-tagged brook trout and rainbow trout. Two-way weirs were placed at the top and bottom of a reach within a section of one of the streams to monitor immigration and emigration of brook trout and rainbow trout. Brook trout catch-per-unit-effort (CUE) using baited minnow traps was more variable when traps were placed near low to high amounts of structure in pools compared to areas with no structure. Whereas, rainbow trout CUE using baited minnow traps was low for all categories, from no structure to high amounts of structure. Brook trout biomass for entire pools was found to be significantly correlated with canopy closure over pools in the absence of rainbow trout (r2 = 0.056, p = 0.037) and in the presence of rainbow trout (r2 = 0.059, p = 0.044). However, no significant correlations were found between rainbow trout biomass for entire pools and various physical features that were measured within pools. The majority of re-captured brook trout (20/23) and rainbow trout (13/15) were less than two pools from the pool in which they were originally captured one month earlier. Primarily young-of-the-year (YOY) brook trout and rainbow trout moved through the two-way weirs. The majority of movement through the weirs was in the upstream direction (74 %) and the majority of the downstream movement (66 %) occurred during the latter third of the monitoring period (July and August). The results of this study may be indicative of responses by salmonids to infertile conditions. The salmonid biomass in streams that are relatively infertile may be at carrying capacity with respect to the chemical characteristics or productivity of the water, but the physical habitat is not likely used to its full potential when compared to more productive waterbodies. Therefore, habitat use and movement patterns exhibited by salmonids inhabiting small infertile streams may be less common, but it may also be the natural response by salmonids that encounter these conditions across their geographic range.