Physiologically based limits to food consumption, and individual-based modeling of foraging and growth of larval fishes

Abstract

Larval fish individual-based models (IBMs) that include foraging subroutines to depict prey encounter, capture and ingestion often include static parameters (e.g. a maximum feeding rate, CMAX) to prevent ‘overfeeding’ and unrealistically high growth rates. We formulated 2 physiologically based approaches to limit food consumption rate (C) based on gut capacity and evacuation rate (GER) and feeding rate-dependent changes in assimilation efficiency (AE ). Parameterizations were based on data reported for a variety of marine and freshwater teleost larvae. The effects of the 3 approaches (CMAX, GER and AE ) on feeding and growth were compared in IBM simulations of 12 mm larval sprat Sprattus sprattus L. foraging within homogenous and patchy prey fields. Prey concentrations for maximum growth were between 5 and 10 copepodites l–1, similar to thresholds determined for successful foraging by larvae of other marine fish species in laboratory studies. The AE limit allowed larvae to exploit prey patches (to consume prey at higher rates but at lower AEs). In simulations using prey concentrations observed in productive areas of the southern North Sea (e.g. 21.0 copepodites l–1), larvae benefited little (benefited much) from adopting this patch feeding strategy when patch prey concentrations were ≤2-fold (≥5-fold) those outside of the patches. At ≤10 copepodites l–1, foraging model predictions of C were close to limits imposed by CMAX, GER and AE methods. In patches (20 to 40 copepodites l–1), foraging model estimates of C were 2to 4-fold greater than the highest (AEbased) limit. Physiological-based limits to C are recommended for larval fish IBMs and will be necessary to adequately assess the impacts of prey patchiness on survival and growth of marine fish larvae.