World’s most endangered marine mammal ‘not doomed to extinction’

If all illegal gillnets were removed immediately, numbers of rare vaquita porpoises could recover, say scientists

Vaquitas are being killed off by fishermen’s gillnets (Paula Olson)

The world’s rarest marine mammal can retreat from the path to extinction if fishermen stop setting illegal gillnets to catch fish, scientists say.

The conclusion contradicts a general assumption that inbreeding among the ocean’s few remaining vaquita porpoises would lead to their extinction regardless of whether gillnetting ended.

It’s thought there are only about 10 vaquitas left on the planet, but the new research suggests their numbers could recover.

Gillnets, which stretch down vertically through the sea like giant tennis nets, are set to catch fish in the Gulf of California in Mexico but they also entangle vaquitas, causing them to drown when they are unable to surface.

But new genetic analysis has found the species has enough genetic resiliency to recover if unchecked gillnetting does not wipe them out first.

"Genomics gives us clues into the species’ past but also lets us peer into the future. Despite the small numbers, the species could recover if we stopped killing them," said Lorenzo Rojas-Bracho, a co-author of the study.

The vaquita, the world’s smallest porpoise, was discovered in 1958, but since then has been rapidly driven towards extinction due to the use of gillnets.

Mexican fishermen set the nets for shrimp and finfish, including totoaba, an IUCN Red List threatened species. The totoaba’s swim bladders are valued as financial investments and for traditional Chinese medicine.

The new research, published in Science, examined the genetic patterns of vaquitas from tissue samples collected by Mexican researchers since the 1980s.

The scientists found that gillnets killed vaquitas too quickly for inbreeding to develop, and those left still reflect the broader genetic diversity of the larger population they came from.

Earlier analysis revealed the species’ abundance fluctuated from a few thousand to around 5,000 for at least 250,000 years, making it naturally rare compared with other marine mammals.

Demonstrators outside the Mexican Embassy in Washington (AFP via Getty Images)

The researchers, from America, Mexico, France and the Netherlands, ran computer simulations on how the population would fare under different scenarios, finding that immediate and complete elimination of gillnets led to a high probability the species would recover.

But even low levels of continuing gillnet-related deaths among the species would rapidly reduced its chances of survival.

A few of the elusive remaining mammals spotted in recent surveys looked healthy, and some had calves, the researchers said.

Phillip Morin, a co-author of the research, said: “The survival of the individuals, and the species, is in our hands.

“There is a high probability genetically that they can recover, if we protect them from gillnets and allow the species to recover as soon as possible to historical numbers.”

Christopher Kyriazis, co-lead of the new findings, added: “If we lose them, it would be the result of our human choices, not inherent genetic factors.”