The gray seal (scientific name Halichoerus grypus) is also known for its excellent diving ability. It usually dives easily for about 20 minutes and can dive for up to one hour. While the ability to dive for a long time is impressive, what is even more surprising is its capability to maintain sufficient blood oxygen levels while diving.
Professor Joanna Kershaw and her research team from the Department of Biology at the University of St. Andrews in Scotland noted on the 21st, "It has been confirmed that the gray seal can determine its dive time by itself assessing its blood oxygen levels." The research findings were published in the international journal Science that day. The seal has oxygen sensors in its body that help prevent drowning.
Mammals need oxygen to survive. However, most mammals cannot detect how much oxygen is in their blood. Instead, they detect a lack of oxygen through increased carbon dioxide levels.
In humans, when carbon dioxide levels increase in the body, sensory organs in the carotid artery detect this, resulting in a response such as shortness of breath. If oxygen is not inhaled at this time, consciousness will eventually be lost.
How do marine mammals, which spend most of their time diving in the water, check their oxygen levels? Professor Kershaw conducted experiments with six wild gray seals. The research team had the seals swim back and forth in a 30-meter-long pool. Before diving, the seals were made to inhale air in a chamber above the water.
There were four types of chambers. One was a chamber containing 21% oxygen and 0.04% carbon dioxide like regular air, while the other two chambers had either half or double the oxygen concentration compared to regular air. The last chamber had standard oxygen levels but with carbon dioxide levels 200 times higher.
The gray seals dived 510 times across all four types of chambers. The average dive time after inhaling once was 4 minutes. The experiment results showed that after being fed in the chamber with high oxygen levels, the seals dove for a longer time, while lower oxygen levels shortened the dive time. In contrast, carbon dioxide levels did not affect the dive time at all.
Dr. Chris McKnight, the first author of the paper, explained, "The seals were aware of their blood oxygen levels and adjusted their dive times underwater accordingly," adding, "The function of detecting carbon dioxide in humans and other mammals can be used in gray seals to detect oxygen levels."
The research team estimated that seals have evolved to have a dulled response to carbon dioxide because they dive more often than humans. Therefore, they can directly sense oxygen levels to regulate their dive times.
References
Science (2025), DOI: https://www.science.org/doi/10.1126/science.adq4921