Originally published 2018-09-14.
Dead olive ridley turtles floating together off the Oaxaca coast in late August 2018, still caught in the net that killed them.
In late August 2018, fishermen working off the Pacific coast of Oaxaca in southern Mexico came across a grim sight: roughly 300 dead olive ridley sea turtles floating in a tight cluster, tangled in a single abandoned fishing net. Mexico's federal environmental enforcement agency, PROFEPA, announced the find on Tuesday 28 August. The net was about 120 metres (393 feet) long, was not an approved type of gear, and the turtles had been dead for around eight days.
The discovery came only weeks after more than a hundred dead turtles washed up in neighbouring Chiapas. Together, the two events turned a spotlight on bycatch and “ghost” fishing gear, two of the biggest threats sea turtles face anywhere in the world.
What was found off Oaxaca
The turtles were spotted near Puerto Escondido, a stretch of coast close to some of the most important olive ridley nesting beaches on Earth. According to PROFEPA's account, reported by EcoWatch, the animals were badly decomposed when they were found, which fits the agency's estimate that they had died more than a week earlier.
The cluster drifted together in the water like a ring of buoys, because they were all still held by the same length of net. Photographs of the scene, like the one above, circulated widely, and international news outlets including the BBC shared the story within hours.
Fishermen in the southern Mexican state of Oaxaca have found about 300 dead sea turtles entangled in fishing nets.
— BBC (@BBC) August 29, 2018
👉 https://t.co/SHfG4F422s pic.twitter.com/G38icWCKIF
Some early coverage listed several possible causes side by side: drowning in nets, swallowing hooks, or poisoning from harmful algae. Those explanations were mostly being discussed for the earlier Chiapas deaths. In the Oaxaca case the evidence pointed much more clearly at the net itself.
A ghost net, not a mystery
Marine biologist Bryan Wallace, a senior scientist at Conservation Science Partners who has studied sea turtles for close to two decades, told National Geographic that the turtles were probably killed by a ghost net: fishing gear that has been lost or abandoned and keeps drifting.
A ghost net does not stop fishing when people stop using it. Fish and turtles become entangled; their bodies attract scavengers and predators, which become trapped in turn. Turtles are air-breathing reptiles, so an animal held underwater drowns. Judging by the different stages of decomposition, Wallace suggested this net had been catching animals for some time.
Wallace also cautioned against simply blaming local fishermen. Many coastal communities in Mexico, he said, are working hard to fish more responsibly under difficult economic conditions. The real problem is structural: gear gets lost, illegal nets go unchecked, and huge areas of ocean are hard to patrol.
The earlier deaths in Chiapas
Oaxaca was the second mass death in the region that summer. Between 24 July and 13 August 2018, 113 dead turtles, most of them olive ridleys, were found along the Puerto Arista sanctuary in Chiapas, about 160 kilometres (100 miles) east of the Oaxaca site.
The cause there was less clear. Some of the animals had injuries consistent with hooks and nets, and experts also raised the possibility of suffocation or toxic algae. Investigations were still open when the Oaxaca turtles were found. Two incidents so close together, both involving an endangered population near its nesting grounds, raised hard questions about enforcement along this coast.
Who the olive ridleys are
The olive ridley (Lepidochelys olivacea) is one of the smallest sea turtles, with a shell of about 60 centimetres and a weight rarely above 50 kilograms. It lives in warm waters of the Pacific, Indian and Atlantic oceans.
It is famous for the arribada, Spanish for “arrival”: a mass nesting event in which huge numbers of females come ashore together over a few nights. In Mexico, arribadas now happen at only a handful of beaches, including Playa Escobilla and Morro Ayuta in Oaxaca and Ixtapilla in Michoacán. The turtles found dead off Puerto Escondido may well have been heading toward these beaches.
Its status is a mix of good and bad news:
- Globally, the IUCN lists the olive ridley as Vulnerable, with a declining population, and it is on CITES Appendix I, which bans international commercial trade.
- In Mexico, the breeding population is classed as endangered (at risk of extinction).
- In the eastern Pacific, strict protections in Mexico and neighbouring countries since the 1980s have helped the olive ridley become the most abundant sea turtle in the region.
That is why Wallace described the Oaxaca deaths not as a population collapse but as an alarm bell: a sign that hard-won progress can be undone if gear and enforcement problems are ignored.
Bycatch and ghost gear: a global problem
It helps to separate two terms that are often blurred together:
- Bycatch is the accidental capture of animals that fishers were not targeting, such as turtles, dolphins, sharks and seabirds caught in nets or on hooks set for other species.
- Ghost gear is lost or discarded fishing equipment that keeps trapping wildlife with nobody attending it. The Oaxaca net appears to have been ghost gear.
The scale of bycatch is enormous. WWF estimates that more than 300,000 small whales, dolphins and porpoises die in fishing nets every year, making entanglement the biggest single cause of death for small cetaceans. For turtles, WWF says that capture in longlines, trawls and gillnets is the greatest threat to most populations, with hundreds of thousands of loggerheads and leatherbacks drowning on longlines set for tuna and swordfish.
Elsewhere, the numbers can be staggering too. In Odisha, India, more than 100,000 olive ridleys were reported dead from fishery-related causes between 1993 and 2003.
Mexico carries a special responsibility here. With long coastlines on both the Pacific and the Gulf of Mexico and Caribbean, its waters host six of the seven recognised sea turtle species (seven of eight if the eastern Pacific black turtle is counted separately). Many of them nest on Mexican beaches.
What actually helps
Stories like this can feel hopeless, but sea turtle conservation has real success stories, and the tools are well known:
- Enforcing gear rules. Nets that are banned in sensitive areas only protect turtles if patrols, inspections and penalties actually happen.
- Retrieving lost gear. Programmes that locate and remove ghost nets, and that make it easier for fishers to report and return lost gear, cut deaths long after a net is lost.
- Turtle-friendly fishing methods. Turtle excluder devices in shrimp trawls, circle hooks on longlines and seasonal closures near nesting beaches all reduce bycatch.
- Supporting fishing communities. As Wallace pointed out, lasting change comes from working with local fishers, not against them.
- Protecting nesting beaches. Guarding nests and limiting lights and development near arribada beaches helps more hatchlings reach the sea.
For readers far from Mexico, choosing seafood from fisheries with credible bycatch controls, supporting groups that remove ghost gear, and never leaving fishing line or nets on beaches all make a small difference. The 300 turtles off Oaxaca died in a single forgotten net; preventing the next one is a matter of making sure fewer nets are forgotten.
Sources: National Geographic, “Hundreds of Endangered Sea Turtles Found Dead Off Mexico” (29 August 2018); EcoWatch, “300 Endangered Sea Turtles Killed in Illegal Fishing Net Off Mexico’s Pacific Coast”; Global Citizen; WWF: Bycatch; Wikipedia: Olive ridley sea turtle; tweet embedded from the BBC.
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