BAY ANCHOVY ANCHOA-MITCHILLI PRODUCTION AND CONSUMPTION IN MID-CHESAPEAKE BAY BASED ON A BIOENERGETICS MODEL AND ACOUSTIC MEASURES OF FISH ABUNDANCE

A growth model of bay anchovy Anchoa mitchilli was developed based on weight and temperature-specific physiological data taken from laboratory and field experiments. The model was adjusted for Chesapeake Bay (USA) conditions to estimate bay anchovy population production and consumption as a function of bay anchovy hatch date, annual mortality, and acoustic measures of fish abundance. Spatially explicit models of bay anchovy consumption were developed to demonstrate how changes in spatial patterning and absolute scaling of the biological and physical environment might affect prey consumption in May and July. In model simulations, bay anchovy grew 3 to 6 % d-1 during summer and fall, and young-of-the-year (YOY) bay anchovy biomass peaked in November (16 270 kg km-2). Weight-specific consumption rate of juvenile bay anchovy was about 60 % d-1 during summer, and population consumption peaked in September (3350 kg km-2 d-1). Population production rate of YOY also peaked in September at 290 kg km-2 d-1, and annual production was 30 770 kg km-2. If all mortality was due to predation, bay anchovy could provide 133 kg food km-2 d-1 for piscivores in November, which could support the maximum daily consumption of 13 300 age-2 striped bass Morone saxatilis per km2. The average trophic efficiency of bay anchovy was 10.7 % with a large seasonal variation (0 to 18 %). Sensitivity analyses identified that weight and temperature-specific consumption and respiration parameters were most sensitive in model simulations of fish growth. Compared with the estimated zooplankton production, the average bay anchovy consumption only accounted for a small portion of daily zooplankton production. But our spatially-explicit model indicated that local depletions of zooplankton were possible due to spatial patchiness of predator and habitat heterogeneity, particularly in July.