From the ABC 7 Weather team

Manta rays facing extinction threat: Study

November 18, 2011 - 05:00 AM
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Conservationists say that manta rays are being fished out of existence, mostly because of the questionable belief that their gills cure disease.

Photo re Manta Ray of Hope

Scuba divers know that there is rarely a bigger thrill than meeting a giant manta ray face to mouth lobes. These sprawling carpets of fish flesh can weigh more than a ton and measure 25 feet between the wingtips, yet they are exceedingly gentle, content to munch on plankton and perform somersaults for the amusement of humans. Ecotourists spend more than $100 million yearly to observe these Heavy Ds of the deep, whose habitat ranges all over the world wherever coral reefs are abundant.

That's why it's so disappointing to see that both species of manta, the huge M. birostris and the smaller M. alfredi, have been placed on the "Red List" of threatened species maintained by the International Union for Conservation of Nature. Previously considered "Near Threatened," a new biological study by the IUCN has determined that the mantas have become "Vulnerable" and now face a "high risk of extinction in the wild." It seems that their slow reproductive cycles – it takes about a year for a mom manta to birth a pup – can't keep up with the pace of the modern fishing industry.

Manta Ray of Hope - Teaser 1080p from Blue Sphere Media on Vimeo.

Manta rays are the train bums of the ocean, wandering over vast distances in their 20-year life span. That makes it hard for scientists to track them and develop strategies to maintain their numbers. But fishermen don't have much trouble finding mantas. According to one estimate, the worldwide manta population has declined by as much as 30 percent in the past few decades.

David Shiffman of Southern Fried Science identifies a big part of the problem: Asian medicine. He writes:

Although their biology cannot support a large-scale fishery and their behavior makes any fishery inherently difficult to manage, manta rays are very much in demand. At least part of them is: their gill rakers. According to Lucy Harrison, program officer for the IUCN Shark Specialist group, “Increasing demand for these fishes’ filter-feeding system for traditional Chinese medicinal purposes, especially in Hong Kong, is rapidly driving down their population everywhere.”

Manta Ray of Hope gets into the gritty details of this strange antidote:

Although we have not identified scientific evidence that support any claims, Chinese practitioners believe the consumption of gill rakers – called peng yu sai - help reduce toxins in the blood by purifying and cooling it, reducing body temperature and aiding blood circulation. A belief that these gills boost the body's immune system, especially when swine and bird flu make daily headlines, has further boosted demand. One kilogram of gill-rakers from a mature Indonesian manta sells for up to USD200 in the dried seafood markets of China. Its surge in popularity is making dried and ground gill rakers even more valuable than shark fin.

The world is still waiting on a peer-reviewed study on the benefits of manta gills. In the meantime, what can you do to help protect the species? Adopting one is a good start, as is donating to the IUCN.

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