Document Type

Technical Report

Publication Date

6-1989

Publisher

Department of Biological Sciences: University of Nevada, Las Vegas

Abstract

Temporal and spatial patterns of age 0 threadfin shad (Dorosoma petenense) abundance and growth, in the Overton Arm of Lake Mead, were examined to evaluate the effects of resource availability on the young fish. This was part of a larger, game fishery enhancement study (Lake Mead Fertilization Project), designed to assess feasability of increasing survivorship of larval/juvenile shad by boosting phosphate levels, thereby increasing algal and zooplankton biomass, during the shad spawning period. Shad are the primary forage base for the striped bass (Morone saxatilis) and black bass (Macropterus salmoides) fisheries. Weekly samples were taken by night surface trawl with a 1 meter diameter ring net, from early June to mid-August, at 12 stations in 1988 and 21 stations in 1989. To examine vertical distribution, depth series samples were taken with a Tucker Trawl at some stations and dates. Chlorophyll a concentrations and Daphnia pulex egg/adult female ratios, used as indicators of resource availability, were also determined for some stations and dates. Patterns of abundance were analyzed with log-log regressions of shad abundance on resource availability and more complex models including large-scale geographic factors with chlorophyll a. In 1988 shad abundance was not significantly correlated (p < 0.05) with chlorophyll a concentration, or Daphnia egg ratios, but was significantly higher in west-side coves. Conversely, in 1989 abundance correlated significantly with chlorophyll a and Daphnia egg ratios, and the west-side effect was insignificant. Abundance was not correlated with distance from inflow, independent of chlorophyll a, in either year. To conclude, there was an apparent link between resource availability and young shad abundance, with evaluation of this relationship being confounded in 1988 by lowered predation in the west-side coves. There was little temporal or spatial variation in mean length from 20 millimeters total length, possibly due to a combination of net bias and selective predation upon larger fish. Growth rates could not be determined. With regard to vertical distribution, greater than 75 % of the fish were in the top 1 meter of water at night. Size did not vary significantly with depth.

Keywords

Freshwater fishes; Lake Mead (Ariz. and Nev.); Phosphorus; Threadfin shad; Wildlife management; Zooplankton

Disciplines

Aquaculture and Fisheries | Biology | Environmental Monitoring | Fresh Water Studies | Natural Resources Management and Policy | Terrestrial and Aquatic Ecology | Water Resource Management

Language

English