A 100-year flood in a low-gradient stream: Response of the resident and non-resident fish assemblages

Resident fish exhibited higher short-term resiliency than did non-resident fish to a 100 y flood in a low-gradient stream. In Jun. 2008, a substantial flood (400% higher than mean daily discharge) occurred in the Big Manistee River watershed in Michigan. Pre-and post-flood fish communities were sampled at two sites on Bear Creek, a 4th order tributary of the Big Manistee River. One site was low-gradient and dominated by sand; the second site was higher gradient and dominated by large woody debris and fine gravel. At both sites, post-flood fish communities were similar to pre-flood communities (Morisita's Index (Im) ≈ 0.8), especially for resident fish (Im ≈ 0.95). Total Catch Per Unit Effort (CPUE) of non-resident fish declined dramatically (5.2 to 1.4 fish per minute) in post-flood surveys, whereas CPUE of resident fish increased slightly (4.3 to 4.7) post-flood. Individual species response was site-dependent and mixed: CPUE of mottled sculpin and burbot increased post-flood, whereas CPUE of other resident species decreased. Resident non-native (i.e., rainbow trout) and non-resident non-native salmonids (i.e., Chinook salmon) experienced the most negative response, suggesting life-history traits of native fish encompass evolutionary adaptations to better persist through extreme disturbance events as compared to non-native salmonids.