Researchers have discovered that marine creatures, including mammals, birds, and reptiles, tend to swim at similar depths relative to their body size when they are traveling without feeding, as a way to conserve energy.
Researchers from Swansea and Deakin Universities have discovered that marine creatures, encompassing mammals, birds, and reptiles, swim at comparable relative depths when they are moving without feeding to conserve energy.
Dr. Kimberley Stokes, Professor Graeme Hays, and Dr. Nicole Esteban from these universities spearheaded a study involving six institutions across five countries, examining the swimming depths of various species including sea turtles, penguins, and whales. They found that these animals typically swim at depths of about three body lengths from the water’s surface, which helps them find the ‘sweet spot’ that reduces wave formation above and limits the vertical distance they travel.
In contrast, some semi-aquatic animals, like minks, often swim at the surface, where wave generation causes significant energy loss. However, for marine birds, mammals, and reptiles that journey long distances over their lives, it is expected that they will evolve to minimize energy costs associated with transport, especially during extended migrations.
It has been understood for some time that the drag caused by wave formation decreases once an object moves deeper than three times its diameter, but tracking the swimming depths of wild animals has been challenging due to technological limitations.
The recent study, published in the Proceedings of the National Academy of Sciences (PNAS), recorded the near-surface swimming depths to within 1.5 centimeters for little penguins and loggerhead turtles. They also collected motion data and video footage from cameras attached to the animals. This new information was matched with satellite tracking data for the long-distance migrations of green turtles and research findings from other studies on penguins and whales. It showed that these animals swim at ideal depths predicted by physics, whether they are ‘commuting’ to find food or migrating over long distances without feeding.
Dr. Kimberley Stokes from Swansea University, the lead author of the study, stated:
“Certainly, there are instances where an animal’s swimming depth is influenced by other factors, such as hunting for food, but it was thrilling to see that all documented instances of non-feeding, air-breathing marine animals adhered to the expected pattern. This is something that has rarely been documented due to the challenges of collecting depth data from animals that cover extensive distances. Thus, it was wonderful to find sufficient examples that demonstrated a consistent relationship between swim depth and body size across a wide range of species, from 30 cm to approximately 20 m in length.”
