Abstract:

A major challenge in Environmental Impact Assessment is selecting the right indicators to detect impacts during monitoring programs. Monitoring young-of-the-year (YOY) fish metrics in freshwater systems may be good effects-based indicators because they respond quicker than the larger bodied adults to changes in the environment, they are typically less mobile than adults, and they are often easier to sample. We sampled YOY Smallmouth Bass (Micropterus dolomieu) monthly in an area upstream of a reservoir (reference) and downstream of the hydroelectric dam (nearfield) in 2021 and annually from 2015-2022 in the nearfield. We found evidence of multiple cohorts, higher concentrations of mercury, higher levels of δ15N, and lower levels of δ13C in fall 2021 YOY fish. The nearfield displayed similar trends when compared to the reference area. Ontogenetic diet shifts are well documented in YOY Smallmouth Bass and are likely the reason for the differences in chemistry between fish of different ages. Fish lengths from long-term monitoring in the nearfield area varied significantly from 2015-2022. It is probable that sampling time was the main contributor to the year-to-year differences. This presentation will highlight the importance of consistency in sampling time and location when using YOY fish for an effects-based monitoring program. Given the quick response to changes in the environment and the potential for non-lethal sampling, YOY Smallmouth Bass promise to be informative for detecting aquatic impacts.