Variability in Daily Ration Estimates of Age-0 Striped Bass in the Chesapeake Bay

Abstract

Previous studies have developed and applied bioenergetics models to estimate trophic demand for prey by striped bass Morone saxatilis in Chesapeake Bay. Although these models were validated with laboratory studies, no field estimates of daily ration of striped bass were available in Chesapeake Bay for comparison with bioenergetics model estimates. This study estimated growth and daily ration of age-0 striped bass in the upper Chesapeake Bay for two dates (6 and 19 October 1993) using the Eggers model. Experiments on the gastric evacuation rate of captive striped bass at 17°C found that stomach contents were evacuated at a rate of e ^−0.12h , where h is time in hours since feeding. Daily ration estimates only 14 d apart varied by 66% (0.0326 g · g⁻¹ · d⁻¹ on 6 October and 0.0542 g · g⁻¹ · d⁻¹ on 19 October). Bioenergetics model estimates of consumption over this period averaged 0.0559 g · g⁻¹ · d⁻¹. Based on the variability in Eggers estimates, it would require more than two estimates (2.4) of daily ration over this period to estimate consumption to within 25% of the parameter with 95% confidence. However, the bioenergetics model estimate of consumption was within 25% of the average of the Eggers estimates and required significantly less effort to obtain. This study suggests that if bioenergetics models are reasonably corroborated in the field or laboratory, they can provide reasonable estimates of consumption by fish from data commonly collected during fisheries surveys (weight at age, diet), with little additional information (energy content, temperature) and much less effort than daily ration estimates of consumption.