Estimation of Surplus Biomass of Clupeids in Smith Mountain Lake, Virginia

Abstract

Mean annual estimates of the surplus biomass of alewives Alosa pseudoharengus and gizzard shad Dorosoma cepedianum in Smith Mountain Lake, Virginia, were calculated from data on the biomass, growth, and mortality of each clupeid species. Surplus biomass, defined as production over a given time period minus the difference in biomass at the end and beginning of the time period, was determined for each cohort of both prey species. Mean total alewife biomass estimated from hydroacoustic surveys during 1993–1998 was 37 kg/ha. Mean total gizzard shad cove rotenone biomass from 1990 to 1997 was 89 kg/ha. When biomass was coupled with estimated growth and mortality rates, mean annual surplus biomass summed across all cohorts was 74 kg/ha for alewives and 116 kg/ha for gizzard shad. The surplus biomass of alewives barely meets piscivore demand (primarily that of largemouth bass Micropterus salmoides and striped bass Morone saxatilis), whereas predator demand might exceed gizzard shad surplus biomass when prey availability is taken into account.