This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Sea lions, marine mammals belonging to the eared seal family, have to dive to search for food and other resources. Between dives, however, they return to the surface to breathe and recover.
For decades, marine biologists assumed that time spent above water allowed the animals to replenish the oxygen they used while diving, clear carbon dioxide and, in some cases, process accumulated lactate. If this were the case, longer periods of underwater foraging would typically be expected to require extended recovery periods. Researchers at the University of California, Santa Cruz, Bielefeld University and other institutions worldwide recently tested this hypothesis by analyzing the diving patterns of five different sea lion species.
Their findings, published in Proceedings of the Royal Society B: Biological Sciences, indicate that longer recovery periods were not driven by longer dive durations, but rather depended on how deep the sea lions dove. "Interestingly, we hadn't originally set out to investigate what shapes the recovery time of sea lions," Jonas F. Schwarz, first author of the paper, told Phys.org.
"We were comparing the diving behavior of different sea lion species to better understand how the environment and physiology influence foraging strategies. While exploring the data, I noticed that beyond a certain dive duration, the time animals spent at the surface suddenly increased." Initially, the researchers interpreted the results of their analyses as an indication of the so-called aerobic dive limit. This is, simply put, the duration of dives beyond which an increased reliance on energy production without oxygen would cause blood lactate levels to rise in the animals' bodies.
After passing this limit, sea lions would, in principle, require longer recovery periods above water. However, when he looked at it more closely, Schwarz realized that the data did not align with this initial prediction. "The more I looked into it, the less sense the numbers made," he said.
"Eventually, I realized that this apparent threshold was simply the point where shallow dives became increasingly rare, as longer dives tended to be deeper. That made it clear that we need to distinguish between the effects of dive depth and dive duration on the recovery time, and we ended up finding something much more interesting than what we had originally been looking for." To conduct their analyses, Schwarz and his colleagues combined sea lion dive records collected in different countries worldwide over the past 22 years. These records included 374 sea lions belonging to five different species and living in 18 colonies.
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