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There are only 10 vaquitas left in the world, but a genetic analysis suggests the small porpoises aren’t necessarily doomed to extinction – so long as they stop getting ensnared in fishing nets, that is.

As the planet’s smallest marine mammals, vaquitas are especially vulnerable to entanglement in gill nets used in illegal fishing operations in Mexico’s Gulf of California, where they live. The metre-and-a-half-long porpoises weren’t known to science until the 1950s. Since then, they have become one of the world’s most endangered animals.

Marine biologists estimate that even at their most populous, vaquitas never numbered more than a few thousand individuals. By the 1990s, there were just hundreds left. Vaquitas’ naturally small population size reduced their genetic diversity, which researchers worried could lead to offspring that are less healthy than their parents.

“It’s cemented in people’s minds that low genetic diversity is a bad thing,” says at the University of California, San Francisco. “But our study is showing that reality is more nuanced than that.”

To find out if the few remaining vaquitas could rebuild their population, Robinson and her colleagues conducted an analysis of 20 vaquita genomes. The genome samples were primarily collected from deceased animals between 1985 and 2017. Because the samples were collected close in time from an evolutionary standpoint, Robinson says they are probably “extremely similar” to those of the surviving vaquitas.

The researchers then used a computer model to simulate future vaquita populations under different scenarios. They found that when vaquita deaths were reduced by 80 per cent, the species went extinct in more than half of the simulations. But when by-catch deaths completely halted, the species recovered in more than 90 per cent of the simulations.

“I was pleasantly surprised that the model showed that vaquitas have a good capacity to rebound if they are adequately protected,” says Robinson. “I didn’t expect [the results] to be that optimistic.”

While the model found moderate consequences from inbreeding, Robinson says “they’re very moderate and have far less of an impact compared to other factors, like the amount of gill-net fishing pressure”.

at the Center for Biological Diversity in Mexico agrees that the results are “very good news”. Now that there is evidence that vaquitas’ small population size isn’t a certain death sentence, Olivera says this work could spur even more stringent protections for the marine mammals. “Now it’s hard science, it cannot be denied.”

The results give Robinson some hope, but not without pause. “There’s a chance that vaquitas could survive,” she says, “but it’s just contingent on human actions and decisions.”

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