Comparison of Horizontal Acoustic and Purse-Seine Estimates of Salmonid Densities and Sizes in Eleven Wyoming Waters

Evaluations of stocking programs for rainbow trout Oncorhynchus mykiss and cutthroat trout O. clarki in reservoirs and lakes of the western United States are typically made by estimating angler catch rates and total catch of stocked trout. Because these estimates are derived through expensive creel surveys, evaluations are infrequent. Trout management could be improved if a rapid, reliable technique to assess population levels was developed. The objective of this research was to determine if horizontal acoustic estimates of salmonid densities and mean lengths were correlated with data collected simultaneously with a 9.1-m-deep purse seine. During daylight hours of summer (June–September) trout were found in offshore surface waters and typically accounted for greater than 90% of the fish captured there. Salmonids seldom accounted for more than 10% of nearshore trap-net catches. This spatial segregation of salmonids offshore and nonsalmonids nearshore simplified interpretation of acoustic data. Sid...