A functional response model fit to empirical consumption data

Abstract The anticipated empirical consumption level of a target (prey) species by its predators is an important variable when implementing the constant biomass escapement strategy in fisheries management. For a single predator, the projection of empirical consumption will depend, among others, on projected distribution in space–time of the predator, degree of predator overlap with prey, and considerations of fluctuating environmental variables (e.g., temperature) that may affect the consumption rate. Hence, the projected empirical consumption is usually uncertain, as it involves the integration of uncertain space-time data and high-throughput models and sub-models. The inclusion of such modeling frameworks into an overall assessment model is usually non-trivial. The goal of this paper is to approximate estimates of the empirical consumption rate of capelin by cod in the Barents Sea, using an analytical functional response (FR) model. The empirical consumption rate is estimated by integrating projected space-time (biotic and abiotic) data with a cod stomach evacuation model. We consider the time series of empirical consumption rates as observation data, and use an optimization procedure to estimate parameters of the FR model. We assess the model performance by the degree to which derived uncertainty envelopes encompass the input data, and evaluate its prediction ability using data that were excluded in the parameter estimation process. Our results show that the FR model provides good approximations to estimates of empirical consumption. A major advantage of the FR modeling framework is that it facilitates hypothesis testing, uncertainty quantification, and seamless integration of the FR model into an overall stock assessment model for capelin.