September 23, 2016. Vancouver, British Columbia - A new study published in the journal Scientific Reports is sounding alarm bells about the extinction risk for devil rays, just as countries around the world gather to consider regulating international trade of these species. Scientists from Simon Fraser University and Mexican research institutions have collaborated to estimate devil ray population growth rates, demonstrating that these rays are inherently more vulnerable to overfishing than most other species of rays and sharks. This study highlights the urgent need for safeguards and controls on the global trade in devil ray gill plates, most of which are exported to China for use as a medicinal tonic. Such action has been proposed by Fiji and 22 other Parties to the Convention on International Trade in Endangered Species (CITES), which convene in Johannesburg tomorrow to begin deliberations on this and many other trade-related proposals.
“Devil rays grow very slowly and produce just one pup about every two years, making them intrinsically susceptible to overfishing, and at a much higher risk of extinction than most other slow-growing rays and sharks,” explained Sebastián Pardo, a PhD student in the Department of Biological Sciences at Simon Fraser University and lead author of the paper. “Our study demonstrates that the devil ray population growth rate is much lower than previously thought, making these species biologically ill-equipped to withstand current global fishing pressure and demand.”
The nine species of devil rays (genus Mobula) are distributed in warm and temperate oceans around the world. They are very closely related to manta rays, although smaller. The scientists took published devil ray data and available life history information and applied novel statistical techniques to estimate the population growth rate of the spinetail devil ray ( Mobula japanica). Mortality stemming from an artisanal fishery in western Mexico was estimated to be higher than the population’s growth rate, indicating overfishing. This finding aligns with evidence of population decline for other species of devil rays in other regions.
“The gill plate trade is supplied through a variety of fisheries, ranging from small artisanal vessels to large commercial operations, and yet, even low levels of devil ray catch are likely unsustainable,” said Dr. Nicholas Dulvy, co-author of the study and co-chair of the Shark Specialist Group for the International Union for the Conservation of Nature (IUCN). “The low productivity of devil rays is in line with that of mantas, which are sought for the same markets. But, by comparison, devil rays are seriously under-protected around the world.”
Both species of manta ray were listed under CITES Appendix II in 2013, thereby obligating member countries to issue permits for exports only if demonstrated as legally and sustainably sourced. There is anecdotal evidence that ensuing protections for manta rays have in some regions led to increased fishing of devil rays, in the face of persistent demand for gill plates and lack of associated controls.
“Devil rays are very similar to manta rays -- in terms of appearance, biology, and threats -- and warrant similarly stringent protection,” said Sonja Fordham, President of Shark Advocates International, who is attending the CITES meeting to promote the devil ray Appendix II listing proposal. “While news of devil rays’ heightened risk is troubling, CITES Parties have the opportunity in the coming days to take global action that will go a long way toward addressing the mounting threats to these vulnerable animals.”
Photo courtesy of Daniel van Duinkerken