Effects of Environmental Enrichment On the Survival and Movement Patterns of Hatchery-Reared Steelhead

New hatchery practices can impact native California fish populations if they result in behavioral differences or increased survival in the wild. We investigated the movement patterns and survival of steelhead (Oncorhynchus mykiss) that were reared in traditional hatchery conditions at the Mokelumne River Hatchery versus fish reared under more natural conditions – environmental enrichment – to test the hypothesis that fish raised in enriched experimental raceways will behave differently than fish reared under normal hatchery conditions. We implanted ultrasonic tags (V7; Vemco, Ltd.) in 50 randomly selected fish from each group, and deployed an array of 12 receivers in the upper Mokelumne River that connects with a larger estuary array to enable monitoring of fish to the Pacific Ocean.

Performance was evaluated by comparing survival and movement rates, route selections, residency, and movement patterns to quantify potential behavioral differences. To date we have detected 11 fish exiting the upper Mokelumne River, 82% of which were reared under traditional hatchery conditions. Additionally, we have detected a higher number of fished reared in traditional raceways as compared to enriched conditions. Differences in the behavior of these fish provide valuable information that could be used to guide future management and conservation strategies concerning hatcheries.