A team of international researchers has discovered that oceanic manta rays – the largest species of ray on the planet – may dive over 1,200 metres deep to find their way around the ocean, according to a new study published in Frontiers in Marine Science.
The scientists tagged 24 giant mantas in Raja Ampat (Indonesia), Tumbes (Peru), and close to Whangaroa (New Zealand) then reviewed the data that had been recorded.
They noticed that the rays were more likely to dive extremely deep off the coast of New Zealand: of the 2,705 tag-days of data recorded, mantas dived over 500 metres deep on 79 days; 71 of these dives were in the waters around New Zealand.
“Far offshore, oceanic manta rays are capable of diving to depths greater than 1,200 metres, far deeper than previously thought,” says the study’s author Dr Calvin Beale from Murdoch University and leader of the Manta Trust's Raja Ampat Manta Project.
The rays’ diving behaviour also offered a clue as to why they might be plummeting to the ocean floor. The mantas in New Zealand typically did a huge dive in the day after swimming into deeper waters off the continental shelf. They swam sharply down but didn’t spend time at these incredible depths, suggesting they weren’t feeding or hiding from predators. After returning to the surface, some swam over 120 miles in the following few days.
One reason for them to dip so far below the surface could be that they are picking up signals about where they are, such as changes in the Earth’s magnetic field, oxygen, temperature and light levels.
“These dives, which are linked with increased horizontal travel afterwards, may play an important role in helping mantas gather information about their environment and navigate across the open ocean,” says Beale. "By diving down and 'sampling’ these signals, they could build a mental map that helps them navigate across vast, featureless stretches of open ocean.”
In deeper waters, these oceanic clues can be more stable and predictable than at the surface, the scientists say.
Although more research is needed, the study "reminds us that the deep ocean – which regulates Earth’s climate and underpins global fisheries – remains poorly understood but vitally important,” says Beale.
Top image: Oceanic manta ray. Credit: Guy Stevens | Manta Trust
More wildlife stories from around the world
- Oldest living animal ever found suggests Atlantic Ocean is close to tipping point, say scientists
- Scientists resurrect 40,000-year-old organisms from Arctic ice – now they’re worried
- Giant deep-sea beasts aren’t just the stuff of legend – here’s how they got so massive
- Night divers capture rare images of fish carrying stinging anemones in their mouths
