Our research revealed that many marine animals, from little penguins (about 30cm long) to pygmy blue whales (nearly 20m long), travel at depths of around three body thicknesses under the surface.

News Release 16-Dec-2024 New study finds marine animals save energy by swimming in a depth ‘sweet spot’ Peer-Reviewed Publication Swansea University image: ...

The waves were rough on the morning of April 11, but Jorge didn’t hesitate. With steady strokes, the 220-pound sea turtle dove into the Atlantic Ocean—his first swim in open water in 40 years.

Stokes et al. 2024, Author provided (no reuse) Of course, not all swim depths are determined by energy efficiency alone. Animals may dive deeper to hunt for prey or avoid predators.