There are only 10 Pacific porpoises left. But saving species is still possible

Posted on Thursday May 5, 2022 at 9:02 PM

They were thought to be doomed: Pacific porpoises are today the most endangered species of marine mammals. And for good reason, scientists estimate that there are only about a dozen left in the waters of the Gulf of California.

Faced with this observation, many believed that this animal could never recover. In question, the forced kinship of future offspring.

But that theory is now contradicted by a new study published Thursday in the prestigious journal Science. She stresses that despite their low numbers, porpoises do not disappear due to genetic reasons.

On at least one condition: that the fishing practices responsible for their deterioration cease once and for all.

“We try to counter this idea that there is no hope, that there is nothing we can do to save them,” author Jacqueline Robinson told AFP, study director and researcher at the University of California, San Francisco.

The campaign for the survival of the genre especially mobilized the actor Leonardo DiCaprio, and it became a diplomatic issue, the United States putting pressure on Mexico.

– Low genetic diversity –

Of the same family as dolphins, this porpoise measures on average just over one meter long, making it the smallest of all cetaceans. Called the “Vaquita Marina” (small sea cow) in Mexico, this animal lives only in a very limited area, in the northern Gulf of California.

In the twentieth century, it was destroyed by the large gillnets used for fishing, especially the threatened fish itself, and the tuaba, which were in great demand in some countries. Although fishing for this fish is declared illegal, the ban is not always respected.

However, porpoises get caught in these nets, causing them to die.

At the time of their first census, in 1997, they were already only 570.

Today, the species is on the verge of extinction, and some felt its fate was now sealed, due to the inevitable inbreeding.

To confirm this, the researchers analyzed the genomes of 20 porpoises, from samples taken between 1985 and 2017 (mostly from deceased individuals) and preserved since then.

This allowed them to determine that Pacific porpoises have always been a rare species, with a population of only a few thousand over the past 250,000 years.

Therefore its genetic diversity is very low. The result was confirmed by comparing its genome with the genome of eleven other species (dolphins, killer whales, whales, etc.).

“In general, low genetic diversity is a bad thing,” explains Jacqueline Robinson. “But in this case, it’s an advantage for the survival potential of Pacific porpoises.”

– stop the window –

To understand the cause, it is necessary to understand the mechanism that makes inbreeding a problem.

It is caused by a type of harmful genetic mutation. Having one copy of this mutation in an individual’s genetic code is not a problem. On the other hand, inheriting two copies becomes a problem for one’s health.

However, the inheritance of two replicas is more likely when the parents are from the same family.

But today’s porpoises have very few of these harmful mutations in their genetic code.

why? “Because its population has always been very small,” explains the researcher. “So these mutations have historically been eliminated much more efficiently than large populations, where they can persist and remain immune to natural selection.”

Based on this observation, the researchers then ran simulations to estimate the survival chances of Pacific porpoises.

If net fishing stops completely, the risk of species extinction is only 6%.

But if only the catch is reduced, the risk of extinction increases dramatically: even with an 80% reduction in catch, porpoises have a 62% chance of extinction.

If they can still be saved, there is an emergency situation, alert the researchers. “If we lose it, it will be the result of human choices, not genes,” study co-author Christopher Kyriazis from the University of California, Los Angeles, said in a statement.

The scientists believe that their simulations can be applied to other rare species, such as the tiger, the Florida tiger and the Tasmanian devil… which they also hope will bring some hope.

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