COLOMBO — When fishermen in southern Sri Lanka recently caught a giant oceanic manta ray, they needed a backhoe to haul it out of the water once they reached land. Weighing 800 kilograms, or nearly 1,800 pounds, the catch drew much local attention. It sold for 170,000 rupees, or about $470, and soon this endangered animal, Mobula birostris, was cut up into a pile of meat.
This isn’t an unusual occurrence in Sri Lanka, where artisanal fishers catch and kill a large number of manta and devil rays, known collectively as mobulid rays, every year.
A study published last year calculated that this annual catch far exceeds the estimated annual capture of mobulid rays by all global industrial purse seine fisheries combined, indicating a far more serious situation than previously thought.
The nine-year study, by researchers from the Blue Resources Trust in Sri Lanka and the Manta Trust in the U.K., shows how the spinetail devil ray (Mobula mobular) is being fished at rates that are much higher than the species’ natural population growth rate. It also highlights that the average sizes of all mobulids, except for the oceanic manta ray, are shrinking.
But there’s plenty of concern over the fate of the latter: notwithstanding the recent 800-kg catch, landings of oceanic manta rays are predominantly those of juvenile individuals, indicating that fishers are exploiting a potential nursery ground for the species in the waters off Sri Lanka.
Declining populations
Other than the oceanic manta ray, five species of mobulid rays are recorded in Sri Lankan waters: the spinetail devil ray, sicklefin devil ray (M. tarapacana), bentfin devil ray (M. thurstoni), shortfin devil ray (M. kuhlii), and longhorned pygmy devil ray (M. eregoodoo), all of them categorized as endangered on the IUCN Red List.
Mobulid rays, closely related to sharks, mature late and have slow reproductive rates and long gestation periods. This means that even low to moderate levels of fishing can lead to a decline in their population very quickly, said study co-author Daniel Fernando, a marine biologist and co-founder of the Blue Resources Trust. The study provides valuable insights into the various species’ life history, population trends and fisheries in Sri Lanka, highlighting the urgent need to protect them to prevent population collapse, Fernando told Mongabay.
The study was conducted from 2011 to 2020 across 38 fish landing sites around Sri Lanka. The field surveying team first gathered data on catch numbers, body size, sex and maturity status for the five mobulid species. They recorded mobulid rays at 21 of the 38 landing sites, totaling 6,516 individuals.
Of these, the spinetail devil ray was the most frequent species, accounting for 75% of the catches, with 4,898 individuals. The sicklefin devil ray was next (17.1%, or 1,114 individuals), followed by the oceanic manta ray (4.6%, or 299 individuals), bentfin devil ray (1.4%, or 93 individuals), and shortfin devil ray (0.9%, or 59 individuals).
High rates of catch
“What is greatly concerning is that our models estimate that over 1,000 oceanic manta rays, 11,000 spinetail devil rays, 5,000 sicklefin devil rays, and 500 shortfin devil rays have landed at these 38 monitored sites annually,” Fernando said. “When we also consider that Sri Lanka has an additional 883 fishery landing sites, the total annual catch estimates for manta and devil rays is extremely high.”
Another worrying finding from the research is that the individuals being caught are increasingly smaller, “decreasing by 1-2% [in body size] each year, indicating that they may be experiencing unsustainable levels of capture.”
Nearly half of the individuals that the researchers recorded were immature, including some pups. The researchers also documented the first, and to date only, record of the longhorned pygmy devil ray in Sri Lanka.
Mobulid rays are filter feeders, running large volumes of water through their gill plates to catch plankton. Dried gill plates are popular in traditional Chinese medicine, and demand for them has fueled an increase in fishing effort and retention of these species in bycatch fisheries.
“Through interviews with fishers, we found that before the demand for gill plates came about somewhere between 2000 and 2010, fishers often released the large rays entangled in their nets and also avoided putting their gill nets in the ocean if a mobulid ray was seen,” Fernando said. “But now things have changed and they bring them back to shore. The value as fresh meat, or dried meat, is extremely low compared to other fish. The gill plates are the primary driver of the fishery.”
No incentive to stop fishing
Mobulid rays are often landed as bycatch by the gill net fisheries that primarily target skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares) and billfish, according to the study. In Sri Lanka, the most-used gear type in small-scale fisheries is the gill net (56%), which are responsible for an even higher proportion of incidental bycatch.
Many fishers also use gill nets in combination with long lines or ring nets to target yellowfin and skipjack tuna. Getting fishers to give up these highly effective methods will be extremely difficult, especially now, as Sri Lanka experiences the worst economic crisis in its history, said Arjan Rajasuriya, a marine ecologist and a former research officer at the National Aquatic Resources Research and Development Agency (NARA).
Operating a fishing boat is expensive, and fishers have been hit by skyrocketing fuel costs and runaway inflation that impacts on equipment costs, worker salaries and other operating expenses. At the same time, fishery resources are declining, meaning more fishing effort is needed to haul in the same catch as before. So even if mobulid rays in Sri Lankan waters are protected, it would be an uphill task to enforce the law on the struggling fishers, Rajasuriya told Mongabay.
Not a conservation priority
Historically, marine species have often been overlooked for conservation, which has instead tended to focus on the more visible terrestrial wildlife, Fernando said.
“The Asian elephant inhabiting the Sri Lankan wildernesses is also categorized as endangered and there is generally a big uproar when they get killed, but it is sad the same attention is not given to the endangered marine animals such as manta and devil rays, or other similarly threatened sharks and rays including the sawfishes and rhino rays, especially considering that some of them have even much higher threat levels,” he told Mongabay.
“It is not an easy situation in Sri Lanka where we rely heavily on marine resources for both food and income. What will be the future of fisher communities if we allow overfishing and directly cause population collapses? We must transition toward sustainable fisheries management, which would allow us to increase our product value while catching less,” Fernando added.
Rima Jabado, founder of the Elasmo Project that works on shark and ray conservation and chair of the IUCN SSC Shark Specialist Group, welcomed the findings from the recent study as key to guiding mobulid conservation measures in Sri Lanka.
“The recently updated IUCN Red List indicates that the mobulid ray species found in Sri Lanka are threatened, so the work being undertaken to research and monitor shark and ray fisheries like this is critical to gather data that can inform management,” she said. She called on Sri Lanka and other countries to introduce national regulations to effectively protect these species.
Sri Lanka is obliged to do so under regional and international commitments that it has signed up to. This includes the Indian Ocean Tuna Commission, which calls for conservation and management measures for mobulid rays (Resolution 19/03). The Convention of Migratory Species (CMS) also extends protection to mobulid rays from capture under Appendix I, while any international trade of their gill plates requires export permits due to their listing on Appendix II on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, CITES clearly prohibits the issuing of permits if the specimens are obtained in violation of other national commitments such as CMS and IOTC.
Number one mobuild killer
Jagath Gunawardana, a veteran environmental law expert in Sri Lanka, said it’s sad that the country is the number one mobulid killer in the world.
“We should take the Maldives as an example, for they took timely action to protect these magnificent creatures as far back as 1995 and even declared marine protection zones with the intention to protect these magnificent species,” Gunawardana told Mongabay.
He added it’s possible for Sri Lanka to legally protect mobulid rays through either the Fauna and Flora Protection Ordinance (FFPO) or the Fisheries and Aquatic Resources Act by including these species in the respective annexes of protected species. This order can be given by the relevant ministers through a gazette notification, Gunawardana said.
Citation:
Fernando, D., & Stewart, J. D. (2021). High bycatch rates of manta and devil rays in the “small-scale” artisanal fisheries of Sri Lanka. PeerJ, 9. doi:10.7717/peerj.11994
This article by Malaka Rodrigo was first published by Mongabay.com on 9 June 2022. Lead Image: A pile of pectoral fins of mobulid rays courtesy of Daniel Fernando/Blue Resources Trust.
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