Genome study offers hope for vaquita, an endangered porpoise in Mexican waters

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The most comprehensive genetic evaluation to date of the vaquita, the world’s rarest marine mammal, offers a glimmer of hope that this small tropical porpoise native to Mexico’s Gulf of California could avoid extinction despite its dwindling population. population at about 10.

Researchers said this month that genomic data from 20 vaquitas showed that although the species has low genetic diversity – differences in DNA between different individuals – the number of potentially harmful mutations that could put danger his survival by inbreeding was quite low.

The vaquita, first described by scientists in 1958 and now considered critically endangered, is the smallest cetacean, the group including whales, dolphins and porpoises, reaching around 5 feet long and 120 books. Its torpedo-shaped body is gray above and white below with a dark ring around the eyes.

Computer simulations carried out by the researchers to predict the risk of extinction showed that vaquitas, whose population has fallen by more than 99% since the beginning of the 20th century due to human activities, have a strong chance of rebounding if the fishing gillnets are removed from their habitat. Gillnets, large curtains of nets that hang in the water, are used to catch fish and shrimp, but have killed many vaquitas who become entangled and drowned.

“Our key findings are that the vaquita is not genetically driven to extinction, as some have begun to assume,” said co-lead author Christopher Kyriazis, a UCLA doctoral student in ecology and evolutionary biology. of the study published in the journal Science. “These findings are important because they give hope for a species that is on the brink of extinction, a species that many are now abandoning.”

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

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

Vaquitas, which are still actively breeding despite their small numbers, inhabit the northern Gulf of California, also called the Sea of ​​Cortez, between mainland Mexico and the Baja Peninsula.

“Gillnet fishing in vaquita habitat has been banned, but the ban has not been enforced and vaquitas continue to perish in the nets,” said study co-lead author Jacqueline Robinson, a postdoctoral fellow at the University of California at the Institute for Human in San Francisco. Genetic.

The first population estimate, made in 1997, found that there were about 570 vaquitas. The population has since declined by up to about 50 percent per year.

The researchers assessed the genetic health of the species, which diverged evolutionarily from its closest relatives around 2.5 million years ago, by examining samples of 20 individuals obtained between 1985 and 2017, mostly archived from of deceased vaquitas. A concern with such a small population is that unavoidable mating between closely related individuals could increase deleterious mutations detrimental to the survival of the species.

Genomic data indicated that the vaquita population was already relatively small – around 5,000 individuals – for hundreds of thousands of years before the crash caused by human activities, making low genetic diversity a natural feature of the vaquita. species.

It also showed that there was relatively little inbreeding among vaquitas and few harmful recessive mutations that could lead to birth defects upon inbreeding that could jeopardize species survival – fewer than 11 other cetacean species assessed, including the blue whale.

A species of cetacean already seems to have been driven to extinction by humans in recent decades: the baiji, or Chinese river dolphin.

“Due to its shy nature, very little is known about the vaquita,” Robinson said. “The species is at risk of extinction before we even fully know what we are losing, and there is no way to replace it once it is gone.”

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