It was believed that they were doomed to extinction: Pacific porpoises are today the most endangered species of marine mammals.
And not in vain, according to scientists, there are only about ten of them left in the waters of the Gulf of California.
Faced with this observation, many believed that this animal could never recover. The forced kinship of future offspring is questionable.
But that theory is debunked by a new study published Thursday in the prestigious journal Science.
She assures that, despite their small numbers, porpoises are not destined to disappear for genetic reasons.
On at least one condition: to completely stop the fishing methods responsible for their reduction.
“We’re trying to disprove the idea that there’s no hope, that there’s nothing we can do to save them,” author Jacqueline Robinson, study leader and research fellow at the University of California, San Francisco, told AFP.
The campaign for the species’ survival is mobilizing actor Leonardo DiCaprio in particular and has become a diplomatic issue as the United States puts pressure on Mexico.
– Low genetic diversity –
From the same family as dolphins, these porpoises average just over a meter in size, making them the smallest species of cetacean. Called “vaquita marina” (little sea cow) in Mexico, the animal lives only in a very limited area, in the northern part of the Gulf of California.
In the 20th century, it was destroyed by large gillnets that were used to catch fish, in particular totoaba, which itself was endangered, in great demand in some countries. Although fishing for this fish has been declared illegal, the ban is not always enforced.
However, guinea pigs get caught in these nets, which leads to their death.
At the time of their first census, in 1997, there were only 570 of them.
Today, the species is on the brink of extinction and some believed their fate was sealed due to inevitable inbreeding.
To find out for sure, the researchers analyzed the genomes of 20 porpoises from samples taken between 1985 and 2017 (most of them were dead) and preserved since then.
This allowed them to determine that the Pacific porpoise has always been a rare species, and their population has never exceeded a few thousand over the past 250,000 years.
Therefore, their genetic diversity is very low. The result was confirmed by comparing their genome with that of eleven other species (dolphins, killer whales, whales, etc.).
“In general, low genetic diversity is considered a bad thing. But in this case, it represents an advantage to the survival potential of Pacific porpoises,” explained Jacqueline Robinson.
– Stop networks –
To understand why, it is necessary to understand the mechanism that makes inbreeding problematic.
The reason is due to some type of harmful genetic mutation. Having a single copy of this mutation in the genetic code is not a problem. On the other hand, the inheritance of two copies becomes problematic for human health.
However, inheritance of two identical copies is more likely when two parents come from the same family.
But today, porpoises have very few of these harmful mutations in their genetic code.
Why? “Because their population has always been very small,” explains the researcher. “Thus, these mutations have historically been suppressed much more effectively than in 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, then the risk of extinction of the species will be only 6%.
But if only to reduce fishing, the risk of extinction increases dramatically: even with an 80% reduction in fishing, the probability of extinction of harbor porpoises is 62%.
Therefore, if they can still be saved, then an emergency has arisen, warn the researchers. “If we lose them, it will be the result of human choice, not genetics,” said study co-author Christopher Kyriazis of the University of California, Los Angeles.
The scientists believe their simulations can be applied to other rare species such as tigers, the Florida panther, the Tasmanian devil… For which they also hope to offer some hope.