All other oceans are known to contain "hotspots" where predators including seabirds feast on prey.

But the new study -- by a team including Exeter, Heriot-Watt and Réunion universities, and ZSL -- found no such concentrations in the Indian Ocean.

With seabirds facing numerous threats due to human activity, their survival depends on protecting the open ocean.

"Efforts are being made to protect key breeding colonies, but until now little was known about where Indian Ocean seabirds go when they're not breeding," said Dr Alice Trevail, from the Environment and Sustainability Institute at Exeter's Penryn Campus in Cornwall.

"We found that seabirds are extremely mobile outside of breeding times, with no focussed hotspots.

"Marine Protected Areas (MPAs) exist in the Indian Ocean, but the birds in our study spent an average of no more than four days in any of the five largest MPAs per year."

The study collected tracking data on nine seabird species during non-breeding periods.

"These birds mostly prey on small fish, so they are affected by human activities including overfishing and pollution," Dr Trevail said.

"As the birds roam widely and spend much of their time outside national waters, we need international action -- like the recent High Seas Treaty -- to protect them.

"No country can act in isolation to protect these birds."

The study was funded by the Bertarelli Foundation.