Study links physical activity to breath holding in whales
Like runners who improve their lung capacity as they exercise, young whales that are physically active improve their ability to hold their breath during dives, according to findings by a Maui-based whale research group.
The study was a collective effort of the research group Keiki Kohola and whale-stranding organizations across the country. Their work offers explanations for a topic scientists know little about – how young whales develop the ability to stay underwater for long periods of time.
“We’ve long had the idea that there may be a benefit to the high exercise that characterizes young calves, but we didn’t have the pieces to answer the question,” said Rachel Cartwright, the project’s lead researcher and a biology lecturer at California State University-Channel Islands.
Like humans, whales draw oxygen from a protein in the blood known as hemoglobin, as well as from a protein called myoglobin stored in the muscles, Cartwright explained.
Marine mammals have myoglobin levels 10 to 20 times greater than humans, according to the study, published last month in the Public Library of Science.
Once an adult whale dives below the ocean’s surface, it won’t need to resurface for nearly an hour, and some species for twice that long.
“Any whale has a lot of muscle . . . where it can bind oxygen and store it,” said Kristi West, a biology professor and member of Hawaii Pacific University’s whale stranding response group. “It allows them to do more in terms of depth and time. It’s like having a bank account of oxygen on board.”
Myoglobin isn’t alone in contributing to longer dives, but it is “a consistent hallmark of the ability,” according to the study.
Because whale tissue samples are hard to come by, the development of myoglobin has not been widely documented, Cartwright said. Not wanting to disturb live whales, the research team collected tissue from 18 deceased stranded whales over the course of a decade, according to West. Samples came from gray, humpback and minke whales of varying ages from Hawaii and the Mainland.
As researchers analyzed tissue samples, evidence showed connections between physical activity and high myoglobin levels.
According to the study, two major muscles play a role as a whale swims: the epaxial muscle, which is used for the upstroke, and the hypaxial, which is used for the downstroke. The study showed that for both young and adult whales, myoglobin levels were greater in the muscle that controls the upstroke, which takes more effort. Once researchers delved deeper into the epaxial, they found that myoglobin was even greater at the bottom of the muscle, which is under the most strain, Cartwright said.
In addition, the active humpback whale had more rapidly growing levels of myoglobin than the calmer gray whale.
“It’s a trade-off between developing breath-holding capacity and growth,” Cartwright explained. “If a calf is really active it doesn’t grow as fast.”
The different behaviors reveal the strategies whales use to deal with predators they face during their annual migration. Gray whales spend their time getting bigger in the hopes that predators will avoid them, while humpbacks improve their diving and breath-holding abilities to better withstand underwater attacks, she explained.
Based on the results, researchers also wondered whether young whales breach with the goal of improving their diving abilities. Breaching is a phenomenon that continues to muddle scientists.
“We don’t really know why whales breach,” Cartwright said. “It seems to have social meaning in breeding areas. However, for calves, they aren’t ready to mate, so the social context doesn’t apply.”
As for whether increasing myoglobin stores are the cause or the result of breaching, West acknowledged that it’s something of a “chicken or the egg” debate.
“We’re not sure which is driving which, but . . . we definitely think they’re highly inter-related,” she said.
West added that understanding whale diving habits can help researchers decide how to best protect the creatures’ habitats.
“We have a problem in Hawaii with vessels striking humpback whales,” West said. “How long whales can stay down, and what factors contribute to the ability to stay down, this is obviously valuable information as we look at conservation measures and how to best share the ocean.”
Maui residents will have the chance to learn more about whales at this weekend’s 10th annual Whale Tales convention today through Monday at The Ritz-Carlton, Kapalua. For more information on speakers and schedules, visit whaletrust.org.
* Colleen Uechi can be reached at firstname.lastname@example.org.