According to a new study by Rachel Cartwright and colleagues from California State University, Channel Islands, baleen whale calves develop oxygen-carrying myoglobin as they mature, with exercise driving the vital component of early development.

The ability to suspend external breathing and make extended dives is a defining adaptive trait that allows marine mammals access to deeper food sources. Deep-diving marine mammals have elevated levels of oxygen-carrying myoglobin within their muscles, allowing oxygen collected at the surface to be stored in the muscles to support extended dives.

With little known about myoglobin levels in baleen whales, the study authors used muscle tissue samples from 18 stranded baleen whales to determine muscular myoglobin stores in both young and adult specimens. Samples from three different age cohorts and three species of baleen whales were evaluated.

Myoglobin stores

The researchers discovered calves possessed only 20% of the muscle myoglobin stores of adult whales. They also learned baleen whales develop elevated myoglobin levels over the course of maturation.

Comparisons of myoglobin levels between and within muscles, along with differences in myoglobin accumulation rate in very young whales, suggest levels of exercise may influence the rate of development of myoglobin stores in young baleen whales. This provides a potential explanation for bouts of energetically expensive exercise, such as breaching, during early development in some species. The authors believe the vulnerability of specific age cohorts to impending changes in the availability of foraging habitat and marine resources.

"Young humpback whale calves frequently engage in extended sequences of breaching, even at a very young age”, said Dr Cartwright. “These high levels of exercise have always been something of a paradox, given the limitations on maternal energy resources during the breeding season.

This study provides a functional explanation for these high activity levels; this intense exercise drives the development of oxygen stores in the muscle tissue, allowing young whales to build their breath-holding capacity and make sustained, extended dives", she added.