Application of multistate modeling to estimate salmonid survival and movement in relation to spatial and temporal variation in metal exposure in a mining-impacted river

Abstract

Multistate modeling was used to estimate survival and movement of brown trout (Salmo trutta) and westslope cutthroat trout (Oncorhynchus clarkii lewisi) in relation to copper concentrations in the mining-impacted Clark Fork River, Montana. Survival probability in the uppermost river segment, where dissolved copper concentrations frequently exceeded acute criteria for aquatic life (range: 31–60 days > 13.4 μg·L–1), was 2.1 times lower for brown trout and 122 times lower for westslope cutthroat trout compared with survival rates in the lowermost segment that had relatively low dissolved copper (0 days exceedance of acute concentration). Lowest survival for both species occurred in the spring–summer period when dissolved copper concentrations were elevated coincident with higher discharge. Movement among study segments was generally low, and cutthroat trout showed low movement into the uppermost river segment with the most elevated copper levels. Both species showed high rates of movement into tributaries, which coincided with their respective spawning migrations rather than as an apparent avoidance of elevated copper levels. The linkage between survival rate and level of copper exposure for both trout species suggests that additional removal of tailings deposits could improve survival rates.