Mobulas, a Wonder of the Gulf of California, Are Disappearing

WIRED

18-02-2025

Feb 18, 2025 7:30 AM Whether by tracking them with acoustic tags or flying drones, or through exposing the black market for their meat and parts, conservationists are determined to protect the magnificent rays of the Pacific. Photograph:In the eastern Pacific Ocean, mobulas alternate between silent undulation underwater and acrobatic leaps out of it. These magnificent rays are at risk of disappearing due to targeted fishing, being caught as bycatch, and climate change. Scientists at the research collaboration Mobula Conservation are teaming up with artisanal and industrial fishermen to protect them.
Also known as 'Devil Rays,' mobulas are elasmobranchs: a subclass of fish—including sharks, skates, and sawfish—that are distinguished by having skeletons primarily made from cartilage. More than a third of the species in this group are threatened with extinction. Of the nine species of mobulas, seven are endangered and two are vulnerable according to the International Union for Conservation of Nature.
Researchers Marta Palacios, Melissa Cronin, and Nerea Lezama-Ochoa founded Mobula Conservation in 2020 with support from the international charity organization the Manta Trust. 'We do science for action, everything contains a conservation objective,' says Palacios. The marine biologists met years ago on El Pardito Island, in the Gulf of California, whose waters are home to five mobula species. The smallest, Mobula munkiana , has a 1.10-meter wingspan; the largest, Mobula birostris , reaches 7 meters across with its fins extended.
The scientists at Mobula Conservation do everything they can to protect these rays: implanting acoustic transmitters and flying drones over their groups to trace their movements, chasing them to film them underwater, sailing at night to record the impact of fishing bycatch, or uncovering the black market for mobula meat and parts around the world. Lezama has worked for years modeling the critical habitats of mobulas in the Pacific Ocean, and Cronin collaborates with geneticists at the University of California, Santa Cruz to uncover the dynamics of their populations.
A recent study led by Palacios revealed that mobulas are caught in 43 countries and consumed in 35. In Latin America, the rays are fished for food, while in African and Asian countries the demand is for their meat and gill plates because of their popularity in the Asian medicinal market. Tonics made from mobulas are said to treat multiple ailments, although there's no scientific evidence to support their efficacy.
Even when mobulas are not targeted, they can end up in fishing nets as bycatch. Instances of up to 200 rays being caught in a single net have been reported. Between 1993 and 2014, more than 58,000 mobulas were reported caught in the eastern Pacific across the five species that inhabit the region. About 13,000 individuals are caught as bycatch each year by the tuna industry.
It's not known how many mobulas ply the seas, but landings of them suggest severe and rapid declines across species and in various regions. To better understand the situation, Cronin and Lezama study industrial fishing in Ecuador, while Palacios focuses on artisanal fisheries in the Gulf of California. All of these researchers are seeking to unravel the life histories of these animals and to involve fishermen in their conservation. From Research to Action
For 11 years, Palacios has made the Baja California Sur desert his home and mobulas his cause. In 2014, while sailing the Gulf of California, he came across Mobula munkiana for the first time. During five days at sea, hundreds of the rays jumped alongside his boat. 'They were everywhere, jumping all over the place, and no one knew what they were doing or where they were going,' he recalls. The lack of answers ignited the Spanish biologist's curiosity.
Mobula munkiana can form massive aggregations in the sea, with thousands of individuals sometimes grouping together across hundreds of kilometers of ocean. These rays can be found in the eastern Pacific, from Peru to Mexico, where they are nicknamed 'tortillas' because of the sound they make when they return to the sea after jumping out of the water, which is similar to making tortillas by hand.
Of all the mobula species, Mobula munkiana is among those that like to jump out of the water the most. Photograph: wildestanimal/Getty Images
These rays are not the only elasmobranchs that jumps out of the water. Many species do so to remove parasites, clean their gills, or as part of courtship. However, while sharks and manta rays jump alone, M. munkiana jump in groups. They jump year-round, regardless of whether they are newborns, adults, females, or males. 'It probably has different functions within their communication, but we don't understand what they are communicating,' Palacios explains.
In coastal areas, aggregating can be a death sentence for these rays if they coincide with artisanal tuna fisheries that use gillnets and purse seines. And if that were not enough of an existential risk, their biology also conspires against them too: their reproduction rate is slow. Depending on the species, it takes between five and 10 years for mobulas to acquire the capacity to reproduce, and they have long gestation periods of more than 12 months, producing only one offspring at a time. They can go between two and seven years between pregnancies.
Furthermore, in the Tropical Eastern Pacific, 23 percent of the 132 species of chondrichthyans—the class to which elasmobranchs belong—have been found to be highly vulnerable to climate change; the worst affected are species that use the coasts as nurseries, such as M. munkiana . Sea warming encourages ocean waters to separate into layers of different densities, a process known as stratification, which makes it difficult for cold, nutrient-rich bottom water to rise to the top of the sea, which can affect food production.
An aggregation of M. munkiana off the coast at Cabo San Lucas, Baja California Sur, Mexico. Photograph: wildestanimal/Getty Images
Years ago, on the Gulf of California, Palacios began implanting small acoustic devices in rays that transform them into data messengers. Fishermen, hired for the task, capture the animals and then return them to the water. This strategy is known as passive acoustic telemetry, and although seemingly invasive, is carried out with extreme care. Once released, the animals resume their swim.
Each time a tagged animal passes near an underwater receiver, the date and duration of its visit is recorded. With this data, in 2021 Palacio was able to describe for the first time a breeding area of M. munkiana in a bay in the Gulf of California. To further reconstruct the life history of these creatures, the scientist collects testimonies from fishermen and observes their monumental groups using drones.
Palacios sleeps little these days. He spends his nights watching the fishermen of bottom-spotted stingrays, a commercial and legally fished species in Mexico, as they cast their nets into the sea. In those nets, mobulas are caught incidentally. One experiment of his consisted of more than 40 nights documenting the situation and assessing whether the use of lighter nets could reduce bycatch. A Lack of Strict Protection
Because of their supposed medicinal properties, the meat and gill plates of mobulas are increasingly in demand in Asia. Palacios recently led a study to try to understand the magnitude of the problem, which involved 100 surveys and interviews in 19 countries. The research team analyzed data from 75 nations, including photos and records of seizures in Palestine, Somalia, Vietnam, and Hong Kong.
Selling gill plates in a dried seafood store. Photograph: Jonathan Wong for South ChinaThe study revealed that meat is exported from countries such as Bangladesh (to mainland China, India, and Myanmar), Ecuador (to Peru), India, Madagascar, Madagascar, Mauritania, Myanmar (to Thailand), Oman (to United Arab Emirates), Senegal, United Arab Emirates, and Yemen. The highest prices for dried meat—up to $10/kg—were found in Bangladesh and Myanmar, while fresh meat reached $8/kg in Benin, Mexico, Brazil, and the Republic of Congo, with M. mobular and M. alfredi being the most hunted species.
Gill plates are harvested in 14 countries across Africa and Asia, and are imported mainly to mainland China and Hong Kong, where a kilogram can cost $1,260. They also reach Singapore, South Korea, and Thailand.
The researchers also found that although international mobula trade involves 20 countries, only five reported it to CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Since 2013, CITES has allowed regulated trade of mobulas in an effort to prevent their extinction, but trafficking of these animals' meat and parts has not decreased. Some researchers therefore recommend moving to a full prohibition of trade.
Habitat care is also weak. UN biodiversity targets have called for nations to designate 30 percent of their waters as marine protected areas (MPAs) by 2030. While MPAs have increased dramatically in size over the past 15 years, currently only 16 percent of marine habitats critical to sharks and rays fall inside an MPA, and only 7 percent of these habitats are 'no take' zones, where fishing is completely banned.
This story originally appeared on WIRED en Español and has been translated from Spanish.