Researchers from multiple universities have uncovered that marine animals swim at optimal depths to minimize energy expenditure, following a common pattern across species. This significant finding could impact conservation strategies and our understanding of marine life behavior.
Researchers led by Swansea and Deakin Universities have made a groundbreaking discovery revealing that marine animals, including sea turtles, penguins and whales, save energy by swimming at a specific depth relative to their body size during migrations. This energy-efficient swim depth helps these animals avoid creating surface waves, therefore minimizing the drag they encounter.
Kimberley Stokes, a research officer in biosciences at Swansea University, led the research alongside Graeme Hays, a professor in marine science at Deakin University, and Nicole Esteban, an associate professor of marine biology at Swansea.
The team’s findings, published in the Proceedings of the National Academy of Sciences (PNAS), show that many marine species swim at depths around three times their body diameter. This “sweet spot” minimizes energy loss by reducing wave formation at the surface and the vertical distance the animals need to travel.
“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,” Stokes said in a news release. “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 to about 20 m in length.”
The study involved highly accurate tracking of near-surface swim depths within 1.5 centimeters for species like the little penguin and loggerhead turtles, complemented by motion data and footage from animal-borne cameras. Satellite tracking data for long-distance migrations of green turtles and other studies on penguins and whales were also analyzed. The combined data revealed that migrating and commuting marine animals consistently swim at depths that are energy efficient.
This discovery aligns with the concept that additional drag from surface waves minimizes once an animal swims at depths greater than three times its diameter. However, the challenge of tracking wild animals over vast distances had previously limited the ability to confirm this with confidence.
This significant finding offers new insights into the adaptive strategies of marine life and enhances our understanding of how these animals conserve energy over their long migratory journeys. The knowledge could inform conservation efforts by highlighting the importance of swim depth optimization in maintaining the well-being and efficiency of marine megafauna during migration.
The implications of this study extend beyond academic interest; they highlight the intricate balance marine animals maintain to survive and thrive in their environments. Understanding these behaviors is crucial, especially as human activities continue to impact marine ecosystems globally.