Marine Animals Save Energy by Swimming at Optimal Depths, Study Finds
Researchers from Swansea and Deakin Universities have discovered that air-breathing marine animals—including mammals, birds, and reptiles—consistently swim at similar relative depths to conserve energy during long-distance travel.
The study, published in Proceedings of the National Academy of Sciences (PNAS), examined swim depths across species such as sea turtles, penguins, and whales. The research team, led by Dr. Kimberley Stokes, Professor Graeme Hays, and Dr. Nicole Esteban, found that these animals travel at depths of around three body diameters below the water’s surface, a “sweet spot” that reduces wave formation and energy expenditure.
Why Depth Matters
When swimming at the surface, animals experience increased drag due to wave generation, a significant energy cost. However, once an animal dives to depths greater than three times its body diameter, wave formation drag minimizes, creating a more efficient travel path. This principle has long been known in physics but was difficult to confirm in wild animals due to technological limitations.
New Insights Through Advanced Tracking
To overcome these limitations, the team utilized a combination of:
- Animal-borne cameras and motion data to measure swim depths with precision (to within 1.5 cm) in little penguins and loggerhead turtles,
- Satellite tracking data for green turtles during long migrations,
- Additional published datasets on other penguin and whale species.
These methods revealed that marine animals swim at these optimal depths when commuting to foraging areas or migrating long distances, both energy-intensive activities where feeding does not occur.
A Universal Adaptation for Energy Efficiency
The findings are particularly exciting because they highlight a consistent energy-saving strategy across diverse species and body sizes—ranging from 30 cm penguins to 20 m whales.
Dr. Kimberley Stokes, lead author, explained:
“There are, of course, cases where swim depth is influenced by factors like searching for prey, but it was exciting to discover a common pattern across non-foraging marine animals. This relationship between swim depth and body size, predicted by physics, is rarely observed due to the challenges of collecting data over large migration routes.”
Implications for Marine Conservation and Research
The study not only provides a deeper understanding of energy conservation in marine species but also offers a framework for future research on animal behavior during migration. Tracking these energy-efficient depths may help scientists:
- Monitor migration patterns under changing environmental conditions,
- Develop strategies for protecting critical migration corridors,
- Understand how human activity, such as shipping or underwater noise, affects marine travel behavior.
By aligning animal behavior with physical principles, this research sheds light on how marine animals optimize their energy use—a key adaptation for species that traverse vast oceanic distances.