Marine animals swim at the perfect depth to save energy

Tucked away in the vast expanse of our oceans, marine animals are capable of making remarkable journeys. Species like the green turtle and loggerhead turtle travel thousands of miles to return to the beaches where they were born to lay eggs.

Humpback whales migrate seasonally between cold, nutrient-rich waters where they feed and warm tropical waters where they breed and give birth.

Regardless of the species, marine animals use specific strategies to conserve energy. In a recent study, researchers have found a common theme among these animals – they all swim at similar relative depths when traveling and not feeding.

The research, led by experts from Swansea University and Deakin University, highlights how marine species minimize energy loss by swimming in a precise “sweet spot” below the surface.

Swimming patterns in marine animals

The study, led by Dr. Kimberley Stokes, Professor Graeme Hays, and Dr. Nicole Esteban, compared the swim depths of sea turtles, penguins, and whales across five countries.

The results showed that these animals consistently traveled at depths around three times their body size from the surface. This specific depth reduces the amount of energy that could be lost to wave formation and minimizes vertical travel distance – both of which contribute to efficient swimming.

Some semi-aquatic animals, like mink, swim closer to the surface, where wave generation causes significant energy waste. However, for air-breathing marine animals that travel vast distances during migrations or daily commutes, adaptations to reduce energy costs are essential.

Long-standing theory confirmed in wild animals

Physics has long predicted that drag from wave formation decreases significantly once an object travels at depths greater than three times its diameter.

Until now, proving this theory in wild animals posed a challenge due to limitations in tracking their movements.

The researchers overcame these challenges by using advanced tracking tools. They recorded near-surface swim depths within 1.5 centimeters for penguins and loggerhead turtles.

Motion data and video footage from animal-borne cameras were combined with satellite tracking data for long-distance green turtle migrations. Data from previous studies on penguins and whales further supported the findings.

Marine animals optimize swim depth

The study was focused on animals traveling for extended distances while not foraging. These patterns showed a clear alignment with the theoretical optimal depths predicted by physics.

“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,” said Dr. Kimberley Stokes, lead author of the study.

“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.”

Implications for marine travel and conservation

The discovery highlights the energy-efficient swimming strategies that marine animals have evolved over millions of years.

Penguins, whales, and turtles all utilize similar techniques, regardless of their size or species, to reduce energy costs during travel.

For animals covering thousands of kilometers in their lifetimes, such adaptations ensure survival and longevity.

Understanding these patterns could aid marine conservation efforts. Tracking swim depths could help identify migration routes, foraging patches, and key habitats for endangered species.

Conservationists may use this knowledge to create more effective strategies for protecting marine animals and their environments.

Relationship between swim depth and body size

The study’s findings provide a rare glimpse into the consistent relationship between body size and swim depth among marine animals.

From the smallest little penguin, measuring 30 centimeters, to massive whales reaching 20 meters, the same energy-efficient pattern emerges.

This highlights a universal principle of physics that governs the behavior of animals across vast size differences.

Future research directions

While the study focused on non-foraging travel of marine animals, future research may explore how swim depths change under different conditions, such as varying water temperatures, ocean currents, or predator avoidance behaviors.

Advancements in tracking technologies will continue to improve our understanding of marine animal movements and energy conservation strategies.

Marine mammals, birds, and reptiles have evolved to swim at precise depths that minimize energy loss. This new study confirms a long-held theory with real-world data, showing that species as different as turtles, penguins, and whales use the same strategy for efficient long-distance travel.

The work by Swansea and Deakin Universities opens new doors for understanding marine animal behavior and enhancing conservation efforts.

The study is published in the journal Proceedings of the National Academy of Sciences.

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