7029 - Laserfiche WebLink

Home Browse Search

THREATS T SHAD STUDY Job I Background The most important prey species in Lake Powell is the threadf_in shad. Shad were first introduced into Lake Powell in 190-8 and. subsequently became established as the, predominant food item in the diet of all major game species (Hepworth) and Gloss 1976, et al. 1975a, 1975b). Shad are typically pela- gic and are not readilY sampled with conventional entraPnent gear' The major objective of this study was to develop, through midwater trawling, an adequate system for samplincr threadfin shad. Data collected in 1976 and 1977 was used to Oetermine shad population level indices and monitor monthly and yearly population dynamics. Striped bass, a large pelagic predator, were introduced into Lake Powell in 1074 to better utilize the dense population of shad. Established game species tend to be restricted to littoral zones and generally do not occupy pelagic regions of Lake Powell. Shad abundance determined for 1976 and 1971 will be used as a baseline for future comparisons in determining population changes and impacts of an expanding striped bass population on threadfin shad abun- dance. Additional information on shad spawning periodicity has been collected.. Methods .' Trawling was carried out with a 28-foot steel hulled work boat. Two Marco W0650 hydraulic winds -Omered by Vickers hydraulic pimps were run directly from the boat's inboard gasoline engines. Dual controls made it possible to run both winches in tandom or individually. The trawl was designed