The vaquita, first described by scientists in 1958 and now considered critically endangered, is the smallest of whales, the group that includes whales, dolphins and porpoises, reaching a length of about 5 feet and 120 pounds. Its torpedo-shaped body is gray above and white below, with a dark ring around the eyes.
Computational simulations conducted by the researchers to predict the risk of extinction showed that the vaquita, whose population has declined by more than 99 percent since the beginning of the 20th century due to human activities, has a high chance of rebounding if gillnets are wiped out from their habitat. Gill nets, large curtains of nets that hang in the water, are used to catch fish and shrimp but have killed many vaquitas that get tangled and drown.
“Our main finding is that the vaquita is not doomed to extinction due to genes, as some are beginning to assume,” said Christopher Kyriazis, a doctoral student in ecology and evolutionary biology at the University of California and a co-author of the study published in Science. “These findings are important because they provide hope for a species on the verge of extinction, and one that many are now abandoning.”
A particular threat is the overfishing with the gillnets of the endangered fish called the touba. Totoaba swim bladders, which are claimed to be a fertility enhancer, are highly valued in China.
“Dried swimming pool tutuaba is traded on the black market in China for traditional medicinal purposes, and sells for a higher price than cocaine,” said study co-author Philip Morin, a research geneticist at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center.
The vaquita, which is still actively breeding despite its small numbers, inhabits the northern Gulf of California, also known as the Sea of Cortez, between mainland Mexico and the Baja Peninsula.
Study co-author Jacqueline Robinson, a UCSD postdoctoral researcher at the San Francisco Institute for Human Genetics, said.
The first population estimate, made in 1997, found that there were approximately 570 vaquitas. Since then, the population has decreased by up to about 50 percent annually.
The researchers measured 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 obtained between 1985 and 2017, most of them archived from the vaquita that died. One concern with such a small number is that inevitable mating between closely related individuals could increase harmful mutations that are harmful to the survival of the species.
Genome data indicated that the vaquita population was already relatively small – about 5,000 individuals – for hundreds of thousands of years before the collapse caused by human activities, making low genetic diversity a natural feature of the species.
It also showed that there were relatively few inbreeding among the vaquita and few deleterious recessive mutations that may lead to birth defects in inbreeding and that can jeopardize species survival – fewer than the 11 other whale species evaluated, including the blue whale.
One species of cetacean appears to have been driven to extinction by humans in recent decades: the baiji, or Chinese river dolphin.
“Because of her shy nature, not much is known about the vaquita,” Robinson said. “Species are at risk of extinction before we know exactly what we’re losing, and there is no alternative once it’s gone.”