The Effects of limited food availability on the striped bass fishery in Lake Mead

The original range of striped bass (Morone saxatilis) was along the Atlantic Coast. They were introduced into the lower Sacramento River in 1879 and are now also found along the Pacific Coast. A landlocked striped bass fishery was established in Santee-Cooper Reservoir, South Carolina, in 1954, and they have since been introduced into numerous other reservoirs, including Lake Havasu, Lake Mead and Lake Powell on the Colorado River. Striped bass were introduced into Lake Mead in 1969 in response to declines in the largemouth bass (Micropterus salmoides) fishery that occurred during the 1960s and in order to further utilize the forage base of threadfin shad (Dorosoma petenense). Natural reproduction of striped bass was documented in 1973, and a highly successful fishery developed during the late 1970s. Striped bass comprised 40.1% of the total angler catch in 1979. The development of the striped bass fishery in Lake Mead was not without cost. A stocking program of rainbow trout (Salmo gairdneri) and other salmonid species was started in 1969. This was also initiated to utilize the surplus threadfin shad production. The trout fishery was considered good from 1970 to 1975, when they comprised 13 to 19% of the total angler catch. This declined to 1% in 1976, despite increased stocking. Food habit studies conducted during this period revealed that rainbow trout occurred in 23% of the striped bass stomachs. The decline in the trout fishery was attributed primarily to predation by striped bass. The occurrence of other gamefish species in striped bass stomachs was low, but threadfin shad comprised 50% of their diet. Striped bass are noted for their voracious appetites and their ability to exploit shad in limnetic areas of reservoirs. This resulted in over exploitation of shad in Santee-Cooper Reservoir, South Carolina. Shad production is closely linked to phytoplankton productivity because of their planktivorous feeding habits. Phytoplankton productivity in Lake Mead declined considerably after Lake Powell was formed in 1963, and most of the reservoir is now oligotrophic-mesotrophic. Shad in Lake Mead are, therefore, extremely vulnerable to possible over exploitation by striped bass. The purpose of this paper is to describe how rapid growth of the striped bass population altered the relative abundance of threadfin shad and how food limitation may be a factor in limiting future success of the fishery