Marine mammals, birds, and reptiles expend a significant amount of energy in their movements. For instance, humpback whales (Megaptera novaeangliae) can travel up to 5,000 miles annually, while Magellanic penguins (Spheniscus magellanicus) migrate along the coasts of Argentina and Chile in search of food. To conserve energy, migratory animals have adapted to swim at consistent depths while traveling, regardless of their size. This phenomenon is explored in a study published in the journal Proceedings of the National Academy of Sciences (PNAS).
Some semi-aquatic animals, like mink, tend to swim near the water’s surface. This surface-level swimming can lead to energy waste due to wave generation, especially for animals undertaking long-distance migrations. To minimize energy expenditure, these creatures adjust their swim depth to a level greater than three times their body diameter, reducing drag caused by wave production.
Tracking the actual swim depths of wild animals has been challenging, but in the recent study, researchers compared the swim depths of sea turtles and other species with data on whales. The findings revealed that many animals, including penguins, turtles, and whales, maintained a drag-reducing sweet spot by swimming at a depth approximately three times their body diameter, whether foraging or migrating long distances without feeding.
The study’s co-author, Kimberley Stokes, a sea turtle ecologist/conservationist at Swansea University, noted the significance of this pattern in animal behavior, particularly in optimizing energy efficiency during migrations. This behavior allows animals of various sizes to sustain their energy levels for feeding and survival.
“There are of course examples where animal swim depth is driven by other factors, such as searching for prey, but it was exciting to find that all published examples of non-foraging air-breathing marine animals followed the predicted pattern,” stated Kimberley Stokes. “This has rarely been recorded because of the difficulty in retrieving depth data from animals that migrate over large distances, so it was great to find enough examples to show a common relationship between swim depth and body size from animals across the size spectrum from 30 cm [11.8 inches] to about 20 m [65 feet] in length.”
This behavior allows animals, both large and small, to optimize their energy usage for survival and thriving.
Win the Holidays with PopSci’s Gift Guides
