Genome study provides important insight into the endangered vaquita, native to the Mexican Gulf of California

The most comprehensive genetic assessment to date of the vaquita, the world’s rarest marine mammal, offers a glimmer of hope that this small tropical porpoise, native to the Mexican Gulf of California, can avoid extinction even though its population has dwindled to about 10.

Researchers said Thursday that genome data from 20 vaquitas showed that while the species possessed low levels of genetic diversity — differences in DNA between different individuals — the number of potentially harmful mutations that could threaten its survival through inbreeding was quite small.

First described by scientists in 1958 and now classified as critically endangered, the vaquita is the smallest of the group that includes cetaceans, dolphins and porpoises, reaching about 1.5 meters in length and 54 kg in weight . Its torpedo-shaped body is gray above and white below with a dark ring around the eyes.

Computer simulations conducted by the researchers to predict risk of extinction showed that vaquitas, whose population has declined by more than 99 percent since the early 20th century due to human activities, have a high probability of recovering once gillnets are completely removed from their habitat will. Gillnets, large curtains of netting hanging in the water, are used for catching fish and shrimp but have killed many vaquitas, becoming entangled and drowning.

“Our key findings are that the vaquita is not doomed to extinction by genetics, as some are beginning to believe,” said Christopher Kyriazis, a UCLA doctoral student in ecology and evolutionary biology and co-lead author of the study, published in the journal Science. “These results are important because they offer hope for a species that is on the brink of extinction and that many are now abandoning.”

A particular threat is gillnet poaching of an endangered fish called the totoaba. Totoaba swim bladders, said to improve fertility, are prized in China.

“Dried totoaba swim bladders are traded on the black market in China for traditional medicinal purposes and fetch a higher price than cocaine,” said study co-author Phillip Morin, a research geneticist at the US National Oceanic and Southwest Fisheries Science Center Atmospheric Administration.

Still actively breeding despite their small numbers, vaquitas inhabit the northern Gulf of California, also known as the Sea of ​​Cortez, between mainland Mexico and the Baja Peninsula.

“Gillnetting in the vaquita’s habitat has been banned, but the ban has not been enforced, and vaquitas continue to die in nets,” said Jacqueline Robinson, co-lead author of the study, a postdoctoral researcher at the University of California, San Francisco’s Institute for Human Genetics.

The first population estimate, conducted in 1997, indicated that there were approximately 570 vaquitas. Since then, the population has declined by up to 50 percent annually.

Researchers assessed the genetic health of the species, which diverged evolutionarily from its closest relatives about 2.5 million years ago, by examining samples from 20 individuals collected between 1985 and 2017, mostly archived from deceased vaquitas. One concern with such a small population is that the inevitable mating between closely related individuals could reinforce deleterious mutations that are detrimental to the species’ survival.

The genome data showed that the Vaquita population was already relatively small — about 5,000 individuals — hundreds of thousands of years before the crash caused by human activity, making low genetic diversity a natural trait of the species.

It also showed that there has been relatively little inbreeding among vaquitas, and very few deleterious recessive mutations that when inbred can lead to congenital malformations that could threaten the survival of the species – fewer than 11 other cetacean species assessed, including the blue whale.

One species of whale appears to have been driven to extinction by humans over the last few decades: the baiji, or Chinese river dolphin.

“Because of its shy nature, very little is known about the vaquita,” said Robinson. “The species is in danger of becoming extinct before we even know what we’re losing, and once it’s gone there’s no replacement.”

© Thomson Reuters 2022 Genome study provides important insight into the endangered vaquita, native to the Mexican Gulf of California

Ryan Sederquist

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