Adaptive Management in Regulated Rivers: Influencing Survival of an Endangered Cyprinid

Most large river systems are highly modified to provide a suite of goods and services for human users.  Environmental alteration or degradation often occurs as a result of river regulation to the detriment of native fish communities.  Regulatory policies such as the U.S. Endangered Species Act as well as basin-specific legislation have led to efforts to mitigate reductions in fish populations while maintaining civil, municipal, recreational, and commercial benefits of river regulation.  In an attempt to balance these social and environmental demands on increasingly limited aquatic resources, the Glen Canyon Dam Adaptive Management Program was developed.  Managers are currently testing fish population responses to a series of “steady flow” experiments during fall in the Colorado River, AZ, with a specific focus on endangered humpback chub Gila cypha. We assessed survival rates of juvenile and young-of-year humpback chub during these contrasting flows using a Cormack Jolly-Seber mark-recapture model to determine if the experimental conditions altered survival compared to the typical fluctuating hydropower discharges. Results from this and similar large-scale ecosystem experiments can be useful in assessing fish - flow relationships and informing dam operations on other regulated rivers.