Production of bay anchovy Anchoa mitchilli in Chesapeake Bay: Application of size-based theory

Abstract

To evaluate and quantify productivity of abundant bay anchovy Anchoa mitchilli in the Chesapeake Bay ecosystem, daily stock biomass, production, and contribution to predators of young-of-the-year (YOY) bay anchovy were estimated from May 1995 to October 2000, based on tri-annual midwater trawl collections. Empirical allometric relationships were applied to develop size-dependent growth and mortality estimates. Estimated annual mean stock biomass of YOY bay anchovy was lowest in 1996 (17 × 10-3 metric tons [t] wet weight) and highest in 2000 (64 × 103 t). Estimated YOY production varied inter-annually by a factor of 4, ranging from 167 × 103 t in 1996 to 697 × 103 t in 2000. Daily stock biomass levels usually peaked in mid September, while daily production and contribution to predators peaked from mid July to late September. The annual production to mean biomass (P/B̄) ratio, which included the very productive larval stage, was high and ranged from 9.02 to 13.23. Analysis of environmental factors indicated that water temperature and dissolved oxygen were important controllers of growth rate. Inter-annual variability in length-specific mortality was inversely related to mean salinity in the summer and fall, suggesting that salinity controls abundances and spatial distributions of predators on bay anchovy. Results imply that annually variable hydrological conditions and secondary productivity may drive observed variability in recruitment and production of YOY bay anchovy by inducing small but decisive differences in growth and predation mortality on early-life stages.