Researchers discover Raja Ampat's reef manta rays prefer staying close to home—which could help save more of them

The reef manta ray (Mobula alfredi) is a tough swimmer. They can travel hundreds of kilometers to feed themselves. The longest recorded movement for an individual reef manta ray was 1,150km, observed in eastern Australia.

But even though they are able to swim long distances, our study on reef manta rays in Raja Ampat, Southwest Papua, discovered they are more likely to swim short distances. They appear to prefer staying close to their local habitats, strengthening their social bonds and forming distinct populations.

Our research—involving researchers from Indonesia, New Zealand and Australia and published in the Royal Society Open Science journal in April—increases our understanding of this globally vulnerable species.

Policymakers can use our findings to enhance conservation efforts for the species in Raja Ampat waters, which currently are facing challenges due to fishing and tourism.

Why don't reef manta rays roam far?

Our study found reef manta rays occupy three distinct habitats within Raja Ampat. As of February 2024, we recorded 1,250 individual manta rays around Waigeo Island's extensive coral reef ecosystem in the northwest of Raja Ampat; 640 manta rays around the coral reef ecosystem in the southeast of Misool, southern Raja Ampat; and no more than 50 manta rays in the Ayau atoll ecosystem up north.

Within their own habitat, the manta rays tend to move around from one area to another, sticking to relatively short distances within 12 kilometers. They only occasionally make longer trips to similar areas in other habitats across Raja Ampat.

We believe there are a few reasons why reef manta rays in Raja Ampat do not often venture far. The first reason is the presence of natural barriers, such as deep waters—over 1,000 meters below sea level—between Ayau Atoll and Waigeo Island, as well as the sea between Misool and Kofiau, which is 800-900 meters deep.

Traveling through deep waters poses increased risks to reef manta rays due to potential encounters with natural predators, such as killer whales (Orcinus orca) and large sharks, which frequently inhabit deep open water.

The second reason is that each habitat is well-equipped with sufficient resources, such as food and cleaning stations, reducing the need for the reef manta rays to travel extensively.

Our previous research has identified dozens of feeding areas and cleaning stations in each habitat occupied by local populations of reef manta rays in Raja Ampat.

Raja Ampat's 'small town' of reef manta rays

The habits of reef manta rays in Raja Ampat are gradually forming a unique population.