Mantas Go to Great Depths

When you are lucky enough to see giant oceanic manta rays glide past you, you may not give much thought to where they're heading next, but it could be down to 4000 feet. Scientists believe they travel to such depth to pick up signals about their location by sensing changes in the Earth's magnetic field, and data about the oxygen, temperature, and light levels. In deeper waters, these clues can be more stable and predictable than at the surface.

Scientists from Murdoch University tagged 24 giant mantas in Raja Ampat (Indonesia), Tumbes (Peru), and close to Whangaroa (New Zealand), and tracked them diving as deep as 4000 feet. The New Zealand mantas made the long journey down, typically the day after swimming into deeper waters off the continental shelf. They swam sharply down but spent little or no time at these incredible depths, suggesting they weren't feeding or hiding from predators. Call it a bounce dive.

After returning to the surface, some swam over 120 miles in the following few days, guided by information, scientists believe, gained from their dive. (BBC Wildlife Magazine)