Experiments show gray seals can monitor their own blood oxygen levels to prevent drowning

A team of scientists with the Sea Mammal Research Unit, School of Biology, University of St Andrews, in the U.K. has found that gray seals are able to monitor their blood oxygen levels as a means to prevent drowning. In their paper published in the journal Science, the group describes experiments they conducted at a pool with captured gray seals involving changes to oxygen and carbon dioxide levels in the air.

Lucy Hawkes and Jessica Kendall-Bar with the University of Exeter and the University of California, San Diego, respectively, have published a Perspective piece in the same journal issue that outlines the work done by the team on this new effort.

All mammals need air to breathe. Prior research has shown that most land mammals have sensors that respond to the build-up of carbon dioxide in the blood, a sign that fresh air is needed. In humans, the increase in carbon dioxide is sensed by chemoreceptors located near the carotid arteries, triggering symptoms including light-headedness, hunger for air, and panic.

Many marine mammals can stay underwater for much longer than land animals, so the research team wondered if they use other mechanisms to alert them when it is time to come up for air. To find out, they captured six adult gray seals and brought them to a pool for testing.

The experiments in the test pool consisted of coaxing the seals to swim back and forth between a feeding station and a breathing chamber where the mix of oxygen and carbon dioxide could be adjusted. Because the pool was covered, the seals were only able to come up for air in the breathing chamber.

The researchers tested various air mixtures—one where the air was ambient, another with double the normal amount of oxygen, one with half the normal oxygen and the third with normal amounts of oxygen but with carbon dioxide 200 times normal levels.

To measure the response to the changes in air they were breathing, the researchers timed how long the seals remained underwater. They found that the more oxygen in the air, the longer the seals remained underwater; less oxygen conversely led to them staying underwater for shorter periods. They also found that the elevated levels of carbon dioxide had no impact on how long the seals stayed underwater.

The research team suggest their findings indicate that the gray seals have a mechanism that allows them to monitor their blood oxygen levels, and use that as an alarm of sorts, alerting them when it is time to come up for air.

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