Development and Sensitivity Analysis of Bioenergetics Models for Skipjack Tuna and Albacore: A Comparison of Alternative Life Histories

Abstract

This study aims to develop bioenergetics models for two pelagic predators, skipjack tuna Katsuwonus pelamis and albacore Thunnus alalunga by synthesizing existing data on metabolic rate, growth rate, and reproduction. My estimates were contrasted with those calculated from a previously developed bioenergetics model for yellowfin tuna T. albacares and with those from an empirical regression model based on fish morphometrics. Based on observed growth rates and metabolic costs and calculated population size structure, the models predict annual consumption: biomass (Q:B) ratios of 32.4, 19.8, and 13.4 for skipjack tuna, yellowfin tuna, and albacore, respectively. The models predict that skipjack and yellowfin tuna populations allocate 20–24% of consumed energy to somatic and gonad growth, compared with only 6% for albacore. The skipjack tuna model was fairly robust with respect to most parameter estimates, but the albacore model was sensitive to parameters describing swimming speed. Empirical regression models commonly used to predict Q:B ratios produced substantially lower estimates than those given above, possibly because those models are for ectothermic fishes and cannot predict the high metabolic demands of the active, endothermic fishes that I studied. The model results indicate that the different life history strategies of these fishes are manifest in their energy budgets and that contrasts in the population consumption rates are largely due to differences in the size structure of the populations.