Thermoregulation and energetics

Based on several lines of evidence, bowhead whales appear to have metabolic rates that are lower than other similar-sized baleen whales. Low metabolic rates offer some disadvantages, such as slow growth rates, delayed maturation, and long intercalf intervals; however, they also offer some advantages. When food is limited, as in winter, or years with low prey densities, it may be possible for a bowhead to persist for long periods at a relatively low metabolic cost. Selection may have modified the bowhead to store large amounts of lipid in the form of thick blubber, to survive the high variability in the arctic and seasons when “food is virtually lacking” (Chapter 7). That is, a large bowhead whale (with its thick blubber) can likely survive a year or years on its lipid reserves. In nature, however, given the stresses associated with migration, reproduction, and predation, it is unclear how long a bowhead could actually persist on limited nutrition. Kraus and Rolland nicely summarized a strategy for the closely related North Atlantic right whale which applies to bowheads as well, “survive the lean years, and reproduce in the good ones.”