How do seals know when they run out of oxygen to rise to the surface?

A new study shows that marine mammals can sense the amount of oxygen in their blood and change their diving behavior according to this oxygen level. All animals take in oxygen from the air when they inhale, and release CO2 when they exhale. Most mammals cannot directly detect the amount of oxygen in the blood. Instead, they rely on increased levels of CO2 in the blood to signal the need to breathe. Scientists believe that even good divers like seals rely on these cues to regulate their diving behavior. But new tests on gray seals show that the animals respond flexibly to changes in oxygen levels while diving. This may explain why free divers often run out of breath before reaching the surface. To find out whether oxygen levels affect the seals' behavior, scientists created a special area in a swimming pool and kept the gray seal pups before returning them to the wild. In the corner of the swimming pool there is a breathing chamber, keeping the seals away from wind and rain. Very quickly, these seals switched from floating to the surface to breathe to breathing in the chamber. The breathing chamber is surrounded by panels that prevent it from floating above the water, but when swimming 60m below the water surface, these seals will find a feeding trough and can eat fish to their heart's content.

However, some critics believe that there are still many questions that need to be answered before reaching the above conclusion. It is agreed that the data obtained support the study's conclusions, but it is still not really certain. Apparently the seals changed their diving patterns as the amount of oxygen they inhaled changed. However, to understand why low-oxygen dives are shorter, more detailed physiological data are needed. Another opinion is that it is possible that both oxygen and CO2 affect diving time, and more experiments are needed to clarify. They do not think that the seal's response to hypoxia is any different from that of some other mammals, but may just be a stronger response by the same mechanism. In response to these comments, the study's authors suggest that seals do not simply react to extremely low oxygen levels, but can perceive and react to many different oxygen levels. For example, a seal was once observed diving nearly 600 meters. With a surface speed of about 1.2 m/s, if seals only react when oxygen is too low, they will not have time to rise to the surface to breathe. And they also believe that this ability to sense oxygen may exist in many other diving animals. There have been previous experiments on ducks, turtles and crocodiles that showed similar behavior to seals, but those experiments were not qualified to draw clear conclusions like the current study.