Scientists not afraid to speak of the devil
An iconic marine species is facing a perfect storm of threats to its survival. Gabrielle Ahern reports.
Devil rays (Mobula mobular) are a majestic presence in the oceans, and encounters in the wild are a once-in-a-lifetime experience for many divers. Soon, however, even these brief encounters may fade.
Already stressed and endangered from the effects of climate change and ocean pollution, the devil ray now risks being driven to extinction by unregulated fisheries because of its reputation among Asian consumers worldwide as a medicine.
Research led by Dirk Steinke from the University of Guelph in Canada reveals that fishing for the ray’s distinctive gill plates has caused its population to shrink by between 56 and 86% in places such as Indonesia and Mozambique over the past eight years. The notoriety attached to exclusive traditional medicines based on wildlife is believed to have turned dried gill plates into a much sought-after health product in Asia.
Steinke and colleagues estimate that the global catch for dried gill plates soared from 5000 rays in 2011 to 130,000 in 2013, with the products originating from China, India, Sri Lanka, Vietnam, Indonesia and Australia.
Nicholas Dulvy from Simon Fraser University in Canada and his team reported the resulting population decline of the rays ironically boosted demand. Rare commodities fetch a much higher price because of their exclusivity. The results from fish market surveys suggest that monitoring programs managed by the Convention on International Trade in Endangered Species of Flora and Fauna (CITES) are unsuccessful.
Both fishing operators and devil rays cross international boundaries, creating another factor that complicates conservation plans.
Rays, like their cousins, the sharks, are top predators and play an integral role in the ecosystem, but their status is perilous. Dulvy and his team found 107 of 539 recorded skate and ray species are threatened, with not enough data to assess the status of another 256.
Devil rays belong to a family known as mobulids, all of which migrate between tropical and temperate environments. Such movement only increases the pressures to which they are exposed, including mortality from entanglement in shark nets along beaches, and cruel measures to stop them damaging fishing nets and aquaculture farms.
With the gradual creep of climate change, mobulid rays are being impacted by alterations in surface water temperatures, and in future will be competing with other animals for habitat refuges containing the environmental conditions critical to their survival.
Estimating the number of devil rays caught each year is challenging, because most of the captures are underestimated, unregulated or illegal. The United Nations Food and Agriculture Organisation (FAO) reports that catch data collected by fisheries often generalises the identification of animals down to naming them as simply “sharks, rays or skates”, without specifying species.
Devil ray gill plates are usually removed before the seafood products hit the markets, making them difficult to identify after the fact. It can also be impossible at market level to tell the difference between legally and illegally caught specimens.
In some Asian countries, the rays are consumed for meat, skin and cartilage, but the main reason they are targeted is their gill plates.
Conservation efforts in Australia and other countries are providing some protective measures for the species and other mobulids. A few years ago, Brazil and Australia banned their capture. Despite this, Indonesian trawlers have admitted to fishing illegally for mobulid rays in north Australian waters, and gill plate products sourced from Australia have been sold in Asian markets.
Devil rays can live for a long time and their predators are few, but because they are slow to mature and take their time to reproduce, the species is vulnerable to negative impacts in the short term. It usually takes 12 to 13 months for one pup to develop before birth.
“There's a natural mortality, of course, through shark attacks, or whatever it happens to be, but basically it's fisheries,” says Mike Bennett, a University of Queensland marine scientist specialising in vertebrate biomechanics.
“There are so many endangered species that we should be looking after and not harvesting for ridiculous reasons,” says Roger Byard, Chair of Pathology at the University of Adelaide. In a paper exploring links between traditional Chinese medicine and species extinction, Byard reports there is no evidence to support claims traditional medicines based on wildlife products provide any health benefits or cures.
He compares traditional Chinese medicine to the great unknown, and would like every preparation containing an endangered species to be wiped off the face of the Earth. The contents of some traditional medicines, he says, are disguised with different names to intentionally avoid prosecution when imported into Australia.
“I think part of the problem is the rigour we apply to western pharmaceutical preparations is not being applied to the Chinese preparations. A lot is being sold in Australia but we don’t know what the contents are,” he adds.
The Asian traditional medicine market is, like any other, profit-driven. However, some research suggests that stronger regulations to protect devil rays might end up generating even larger cash flows.
Donald Croll from the Coastal Conservation Action Lab at the University of California led a study into fisheries impacts on the devil and manta rays, and reported the global return for mobulid rays as an ecotourism investment is $75 million per year, a vastly different sum compared to $11 million per year for the gill plate trade.