Theoretical model of migration energetics in the blue whale, Balaenoptera musculus

Abstract

Blue whales ( B. musculus ) of the southern hemisphere migrate from high latitudes (Antarctic region, feeding grounds) to low latitudes (Tropical region, breeding areas). The possible energy saving of living in warm waters during non-feeding days, relative to the energy cost of swimming to them, is assessed using thermal and hydromechanical models. The thermal model equates size-dependent metabolic cost as a function of ambient temperature with the temperature at which the animal first becomes thermoneutral with respect to its environment (lower critical temperature). By incorporating an expression describing the relationship between latitude and sea temperature, size-dependent metabolic rate and lower critical temperature are expressed in terms of range. Likewise, the hydrodynamic model equates swimming cost as a function of size, swimming speed and range. It turns out that within a myriad of possible strategies concerning distance and swimming speed, there is one that is optimal for minimizing the total energy cost associated with the non-feeding days for an animal of a given size. Literature values for migration distance and swimming speed in relation to size support the results of the model. A basic result predicted is that regardless of size, the animals should migrate to where they are thermoneutral, rather than stay in the Antarctic waters. However, the relative energetic advantage is greater for smaller whales. Similar results are given by an energy input/output model.