Health and movements of fish in response to sediment sluicing in the Wind River, Wyoming

A study of the effects of a sediment sluicing operation on the fish population of the Wind River, Wyoming, was conducted in 1991 and 1992. Sluicing from a lowhead diversion dam resulted in dramatic increases in suspended solids. Maximum suspended solid concentrations directly below the dam were as high as 18 000 mg/L (up to 1200 times mean concentrations recorded during normal low-flow conditions). Values from a sediment stress index indicated that sediment concentrations and durations were sufficient to cause behavioral, sublethal, and lethal responses in salmonids. A necropsy-based assessment of fish health showed significant signs of stress in mountain whitefish (Prosopium williamsoni) downstream of the dam. Negative physiological effects attributable to high suspended solid levels were seen in both internal and external examinations of the fish. Salmonid movement was measured by recapturing tagged fish. Fish above the dam moved an average of 1.8 km; those below the dam moved an average of 4.3 km. The increased movement of tagged salmonids below the dam was attributed to the sluicing operation. Fish population and community indices reflected a decline in species with specialized feeding and reproductive needs in the degraded habitat below the diversion dam.