The optimal allocation of time over the dive cycle: An approach based on aerobic and anaerobic respiration

Houston and Carbone (1992, Behav. Ecol., 3, 233-262) developed models that predict the optimal allocation of time during the dive cycle motivated by the assumption that the diver uses aerobic respiration. In this paper this approach is extended using a model based on maximizing the proportion of time spent foraging to allow for the additional use of anaerobic respiration. Two models are presented. One, the 'switch' model, assumes the diver uses only one of the two metabolic pathways during a dive. This model predicts the travel time (or water depth) at which the diver switches from aerobic to anaerobic dives. Another, the 'mixed metabolism' model, assumes a simultaneous mix of the two metabolic pathways and predicts a shift in the proportional use of aerobic and anaerobic respiration with increasing water depth. In the mixed metabolism model, the predicted time in the food patch can change from a pattern qualitatively similar to the previous models, first increasing and then decreasing with depth, to a novel pattern with two peaks. The second peak in foraging time appears to be largely fuelled by anaerobic respiration. The corresponding time on the surface changes from a pattern similar to the former models with one region with an abrupt upturn to a pattern with two such regions. These models provide insights into issues currently debated among diving physiologists concerning the degree to which and when divers should rely on anaerobic respiration.