Deep-diving marine mammals, like baleen whales and some seals and sea lions, have elevated levels of the oxygen-carrying protein myoglobin within their muscles. This allows them to collect oxygen at the surface to store in the muscles for supporting their long, extended dives. Young baleen whales develop high myoglobin levels as they mature, and according to a new PLOS ONE study, exercising helps drive the development of these myoglobin stores.

By not having to come up for air that much, marine mammals can exploit deeper food sources. Their myoglobin levels are between 10 and 20 times greater than their terrestrial counterparts. Previous work revealed that levels of muscular myoglobin can vary a lot during the development of sea lions, seals, dolphins, and porpoises, but little is known about myoglobin levels in baleen whales. 

To investigate, a team led by Rachel Cartwright of California State University Channel Islands examined samples of muscle tissue collected from 18 stranded whales. These included calves, juveniles, and adults from three different species: minke (Balaenoptera acutorostrata), humpback (Megaptera novaeangliae), and gray (Eschrichtius robustus) whales. The team also compared myoglobin levels between and within the muscles, and they studied the differences in myoglobin accumulation rate in the young whales. 

^{Sampling sites used for the provision of muscle tissue samples. Yvette Hansen}

The development of elevated myoglobin levels is prolonged over the course of their extended maturation. The calves have between 17 and 22.8 percent of the muscular myoglobin stores of adults, and juvenile myoglobin levels ranged between 28 and 60 percent of adult levels.  

The team also found that levels of exercise may influence the rate of development of myoglobin stores in some young whales. While gray whale calves are quiescent and aerial behaviors are rare, bouts of energetically expensive exercises – such as breaching (pictured above) – occur frequently during the early development of humpbacks. In fact, it’s common to see 30 or more consecutive breaches. 

"Young humpback whale calves frequently engage in extended sequences of breaching, even at a very young age. These high levels of exercise have always been something of a paradox, given the limitations on maternal energy resources during the breeding season," Cartwright explains in a statement. "This intense exercise drives development of oxygen stores in the muscle tissue, allowing young whales to build their breath-holding capacity and make sustained, extended dives."