Striped Bass Dispersion and Effects on Fisheries Management in Lakes Mohave and Pleasant, Colorado River Basin
William T. Stewart and Mike Burrell
Abstract.—The striped bass Morone saxatilis was introduced into the lower Colorado River in the late 1950s and into Lake Mead, Nevada and Arizona, in the late 1960s. The unintended immigration of striped bass into Lake Mohave, Nevada and Arizona, on the main stem, and Lake Pleasant, a tributary reservoir in central Arizona, has resulted in changing management practices. Striped bass entered Lake Mohave via downstream emigration from Lake Mead through Hoover Dam at various life stages, and the newly established population quickly became the primary sport fish in the reservoir. Predation from the striped bass population in Lake Mohave coincided with elimination of threadfin shad Dorosoma petenense and a rapid decline in the survival of stocked rainbow trout Oncorhynchus mykiss. Striped bass are also believed to be hindering ongoing efforts to reestablish the native endangered species razorback sucker Xyrauchen texanus and bonytail chub Gila elegans. Striped bass gained access to Lake Pleasant via Lake Havasu, California and Arizona, by way of the Central Arizona Project (CAP) Canal. Operation of the CAP Canal began in 1985 and the canal was fully connected to Lake Pleasant in 1992. In 1986 and 1989, striped bass population densities in the CAP Canal were estimated at 70 ± 37 fish/ha and 3 ± 1 fish/ha, respectively. Striped bass were first captured in Lake Pleasant in 1998 during a gill-netting survey. Catch per unit effort increased almost yearly from 0.13 fish/net-night in 1998 to 6.74 fish/net-night in 2005. Since their unintended introduction into both reservoirs, striped bass have established viable reproducing populations. Management efforts have emphasized promoting harvest and minimizing the impacts of striped bass on existing fisheries. These experiences provide guidance for evaluating unintended dispersion of striped bass elsewhere.