INDIVIDUAL-BASED MODELING OF RECRUITMENT VARIABILITY AND BIOMASS PRODUCTION OF BAY ANCHOVY IN MID-CHESAPEAKE BAY

Production of bay anchovy Anchovy mitchilli is highest in the larval a nd juvenile stages. The interplay between vital rates, stage durations , prey resources, and anchovy abundance ultimately determines the rela tive magnitude of recruitment (which in the model varies by about thre e-fold) and of stage-specific production. Changes in adult seasonal sp awning patterns that increase the number of larval survivors result in only a slight increase in overall production due to density-dependent decreases in growth rates of later life stages. Bay anchovy in the mi d-Chesapeake Bay may reach a compensatory threshold during late summer -autumn as fish growth is affected by competition for food resources. Density dependence in the population is evident in the relationships b etween spawner-recruit, size-recruit, and production of larval or juve nile to young-of-the-year life stages. Density-dependent growth acts d ifferentially upon the early life stage that exceeds the compensatory threshold in any given year, due either to environmental variability o r population size, or both. This could explain partially the relativel y low recruitment variability observed for this anchovy. (C) 1997 The Fisheries Society of the British Isles.