Protected areas could help world's biggest ray to bounce back

Crowdsourced photographs are helping to demonstrate the value of nature reserves to the world's largest ray.

With wingspans measuring longer than a London bus, giant manta rays are among the biggest fish in the world. However, demand for their gill plates in traditional medicine has pushed their populations into decline.

New research in Indonesia has found that protecting their feeding grounds and courtship areas can help the species thrive, with over 1,000 animals found within the waters of Komodo National Park. The researchers behind the study have called for extra protections to help populations of giant manta rays and their close relatives recover.

Ande Kefi, a co-author of the study published in the journal PeerJ, says, 'This study shows that the places where tourists commonly observe manta rays are important for the animals to feed, clean and mate. 

'This means that the Komodo National Park should create measures to limit the disturbance at these sites. I hope that this study will encourage tourism operators to understand the need for the regulations already imposed and increase compliance.' 

What are manta rays?

There are two species of manta ray, the giant manta ray and the reef manta ray. Like the sharks, rays are elasmobranchs, and possess skeletons that are mostly made of cartilage rather than bone.

Their name is derived from the Spanish word for large blanket, reflecting their shape as very wide, thin fish which glide through their water. The wing-like movement of their large fins is reflected in the name for a group of manta rays, known as a squadron.

The rays can be found all across the tropical oceans of the world, and migrate large distances underwater at speeds of up to 24 kilometres per hour. Their shape and speed means that their only natural predators are large sharks.

Though they can move relatively fast, their reproduction is comparatively slow, giving birth to one pup every four to five years. This has hindered the ability of the species to recover as the impact of fishing has increased in recent decades.

While the manta rays are accidentally caught, there are also fisheries that specifically target the animals due to the demand for its gill plates in traditional medicine in southern China, where prices can reach up to £281 per kilogram.

Unfortunately, this trade is believed to be expanding, putting pressure on populations of manta rays. In 2020, this saw giant manta rays classed as Endangered, moving them one step closer to extinction. 

In Indonesia, where ray fisheries were formerly widespread, concerns over the health of the species saw ray fishing banned in 2014. While some illegal fisheries persist, the country has sought to encourage manta ray tourism instead, which is estimated to be worth over £12 million a year to its economy.

One manta ray tourist hotspot is Komodo National Park, a world heritage site famed for the Komodo dragon. The researchers behind the latest study wanted to assess if the conservation area was helping rays.

They found that the site is essential not just for local manta rays, but for these fish across the waters of southeast Asia and beyond. 

How does Komodo National Park help manta rays?

The researchers behind the study made use of photographs taken by the public to estimate the number of manta rays in Komodo National Park. Manta rays have a random pattern of spots on their underside, which can be used to identify them in a way similar to fingerprints for humans.

Co-author Dr Andrea Marshall says, 'People love manta rays - they are one of the most iconic animals in our oceans. The rise of the number of people engaging in scuba diving, snorkelling and the advent of affordable underwater cameras meant that photos and videos taken by the public during their holidays could be used to quickly and affordably scale data collection.'

From photographs taken between 2013 and 2018, researchers were able to identify 1,085 manta rays were across 14 sites within the national park. Some of these sites were cleaning stations, where manta rays gather to have dead skin and parasites eaten by small scavenging fish. 

These cleaning stations were closely linked by the study to courtship behaviour and lekking, where males gather to compete for females. The team even think that one site may be a ray nursery, but this could not be fully confirmed. 

The scientists found that rays tended to stay closer to certain sites, with some general mixing. This suggests that rays could have preferences for certain regions and that preventing interference in these areas could help preserve the species.

Lead author Dr Elitza Germanov says, 'I found it very interesting how some manta rays appear to prefer spending their time in some sites more than others, even when sites are five kilometres apart, which are short distances for manta rays.'

'This means that manta rays which prefer sites where fishing activities continue to occur or that are more popular with tourism will endure greater impacts.'

The researchers suggest that manta rays in Komodo National Park could be spreading into adjacent areas and helping to repopulate other sites in Indonesia and the wider oceans. They recommend further protections for the rays in national parks to ensure populations stabilise and thrive.