The Population of Vaquita Porpoises Has Dwindled to Ten, but a Rebound Isn’t Out of the Question

If protected from illegal fishing, scientists say the critically endangered species has enough genetic diversity to recover

An image of a vaquita porpoise underwater.
Over the past decade, vaquita numbers plummeted from 576 to just ten individuals because of a rise in the illegal totoaba trade. Alfokrads via Wikimedia Commons under CC BY-SA 4.0

The vaquita (Phocoena sinus) is the world's most endangered marine mammal species. Considered a national treasure in Mexico, where it's found in the upper part of the Gulf of California, the porpoise is known for its small size, at four to five feet long and 100 pounds, and the grey and black markings on its eyes and snouts. The mammals were first declared "vulnerable" by the International Union for Conservation of Nature (IUCN) red list in 1978, but are now on the brink of extinction as only ten individuals remain.

An international team of researchers argues, however, that it's not too late to save the rare species. Their study published this month in Science found that, despite its small population size, the vaquita stands minimal risk of harmful mutations caused by inbreeding. 

Over the past decade, vaquita numbers plummeted from 576 to just ten individuals because of the rise in the illegal totoaba trade, reports the Guardian's Karen McVeigh. The "little sea cows" are ensnared in gillnets set up by poachers in pursuit of totoaba—an endangered fish that fetches thousands of dollars on China's black market for its swim bladder, which is considered a delicacy.

To get a better picture of how the vaquita porpoise could rebound, the researchers sequenced and analyzed 20 vaquita genomes taken from archived tissue samples, Kendal Blust reports for NPR. From the analysis, the team found slight genetic variation between the vaquitas because the population numbers have historically been low. Vaquita porpoises were first discovered in 1958, and the cetaceans are endemic to the northern end of the Gulf of California. The species' population remained under 5,000 individuals for tens of thousands of years due to its small habitat range.

"The fact that they've had low population sizes and low genetic diversity for a very long time in their evolutionary history kind of gives them an edge for rebounding from this current extreme population decline," Jacqueline Robinson, an evolutionary geneticist at the University of California, San Francisco and study co-author tells NPR. "They have less hidden, harmful genetic variation that could become a problem with future inbreeding."

The team used the genetic analysis and what is known about the porpoise's life span and reproductive behavior to model and simulate population growth and decline depending on the number of gillnet deaths. If the vaquita is protected and the gillnet deaths stop completely, the team estimated that there would only be a 6 percent chance that the porpoise would go extinct in half a century, NPR reports. But if the mammals continue to be trapped in the nets, even at small levels, the likelihood of extinction increases. Chris Kyriazis, an ecologist at UCLA and study co-author, tells NPR that even with an 80 percent reduction in gillnet deaths, the chances for the vaquita's survival still drop considerably.

The vaquita's habitat in the Gulf of California is protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) signed by Mexico in 1991. Other protection efforts included a program announced by former Mexican President Enrique Peña Nieto in 2015 that banned gillnet fishing for two years in the vaquita's known habitat. Some areas have a zero-tolerance policy for gillnet fishing, though it is not always enforced, per the Guardian. Totoaba fishing was banned in Mexico in 1975, but illegal fishing still occurs because dried totoaba swim bladders can fetch prices of $46,000 per kilogram.

Still, researchers hope the vaquita can recover if the fishing completely stops. "This [study] adds to the argument that the species can be saved, they can recover, even though there are only a few individuals left," Alex Olivera, a senior scientist and Mexico's representative of the Center for Biological Diversity, tells NPR.

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