Endangered 800kg giant manta ray, worth ‘more alive than dead’

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https://www.sundaytimes.lk/220508/news/endangered-800kg-giant-manta-ray-worth-more-alive-than-dead-481968.html Published on SundayTimes on 08.05.2022

It is a difficult time for everyone, so the fishermen of the boat ‘Sehansa’ that left Mirissa harbour on May 1, prayed for a good catch. The ocean deity Poseidon would have heard their prayers. They hauled in a giant manta ray and sold it for Rs 170,000. To offload the 800 kilogram fish, they had to use a backhoe.

The fish was netted about 25 nautical miles offshore, so dragging it back to shore was a struggle. It took about 15 hours for the boat to reach Mirissa harbour, according to its skipper Ranjith Abeysundara.

The giant Manta Ray Pic by Tharanga Gunarathne

“But manta ray is a marvel of nature, and it would be worth more alive,” said Daniel Fernando of the Blue Resources Trust, an expert on rays and sharks.

He confirmed that what was caught by Mirissa fishermen was a giant manta ray, scientifically called mobula birostris. Manta rays are an important attraction in marine tourism because of their enormous size and they are easily drawn to humans.

In the Maldives, rays are a key tourist attraction and operators for manta ray watching are estimated to generate over US$73 million a year with a direct economic impact, including associated tourism earnings of US$140 million a year, according to a 2013 study on ‘The Global Economic Impact of Manta Ray Watching Tourism’.

Manta rays are a migratory species, so the one caught by the Mirissa fishermen could be one that was part of an attraction elsewhere. The creature could have a greater economic value alive than the Rs.170,000 it was sold for, according to experts.

Rays and skates are usually bottom dwellers, but the manta rays glide in open oceans, so it is also called oceanic manta ray, says Mr Fernando.

Forty-two species of rays are known to live in Sri Lankan waters both inshore and in the ocean and the giant manta ray is the largest of them all.

According to available literature, the giant manta ray can grow to a disc size of up to 7 m (23 ft) across. It can weigh about 3,000 kg, but the average size is 4.5m (15 ft). So in that sense, the one caught in Mirissa could have grown to be a bigger creature.

Research has found that manta rays feed on plankton, filtering them through the ocean waters as they swim with their mouths open, but they also feed on fish on occasions. Manta rays filter feed using gill plates, which are cartilage filaments. These are being used in traditional Chinese medicine, so there is a demand for the dry gill rakers, which also has led to them being purposely targeted. But they often become by catch in commercial fishing.

Manta ray, like most sharks, are slow breeders. The female usually gives birth to a single pup and it has about a 12-month gestation period, records show.

“So, when we catch manta ray unsustainably, their population quickly declines. This species is already categorised as ‘endangered’ in the global red list,” Mr Fernando told the Sunday Times. The fish was elevated to the ‘endangered’ list only in 2020. Overfishing has become the main threat.

In Sri Lanka, the elephant and leopard are categorised as ‘endangered’ and there is a big uproar when such animals get killed.

“But it is sad the same attention is not given to ocean creatures such as manta ray, even though they have the same threatened levels,” Mr Fernando noted.

A recent global assessment which was done over years found that a third of shark and ray species have been overfished to near extinction. Scientists points out that sharks and rays are the indicators that the fisheries reach unsustainable level and if no action is taken, more oceanic creatures would face extinction.

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