Vaquitas are among the most endangered animals on the planet, with only 10 individuals still alive. Related to harbor porpoises, the mammals are about five feet long, small enough to be threatened by fishermen using gillnets in Mexico’s northern Gulf of California, the only place in the world where they occur. These finely woven massive nets are used to catch shrimp and fish, but all too often they also entangle vaquitas.
With so few vaquitas remaining, many researchers fear that the population may not recover genetically, even if gillnet fishing, which is illegal in the area where vaquitas still occur, stops. A study published on May 5 in the journal Science does, however, contain some positive news: it suggests that the genetic diversity of the species has long been quite low and therefore vaquitas may be less vulnerable to inbreeding than many other species.
Using a model to explore the probability of the population surviving under different conditions, the researchers show that in scenarios where no more vaquitas die in the nets, there is only a 6% chance that they will disappear. But preventing more vaquitas from dying is urgent. This part of the story is unfortunately less encouraging.
“This is a really exciting study,” says Barbara Taylor of the US National Oceanic and Atmospheric Administration, one of the authors, “because it gives scientists new tools to ask themselves if this species is really doomed. extinction because of genetics, or whether we should care about other things.
“All conservation is about changing human behavior,” she adds. “If it has an economic cost and people can use the excuse that they are doomed anyway, that is bound to be a barrier to action.”
Change speed
Today, vaquitas only live in a very small area, about 15 miles long and 7.5 miles wide, in the far northern Gulf of California, says Taylor, who surveyed the area in 2019. and 2021. Gillnets have long been illegal there, but bans are not enforced, she says.
“People were still setting and retrieving their gillnets, and no one tried to hide it.” The only legal way to catch blue shrimp from small boats at the moment is to use small trawlers instead of gillnets, but Taylor says no such gear has been seen in northern gulf and that all the prawns were still caught by gillnets. These shrimp would be sold to industrial shrimpers so that they could still be exported, mainly to the United States.
An earlier effort to convince local fishermen to switch to vaquita-safe fishing gear began to show promise about 10 years ago, Taylor says. “Everything came to an abrupt halt when people started fishing for totoaba,” a large rare fish considered endangered in Mexico and illegal to harvest. Some people in China believe that swim bladders of this species have medicinal benefits, despite a complete lack of scientific evidence. But the astronomical prices that bladders command have led to the involvement of organized crime in regional fisheries, making the use of gillnets even more difficult to control.
As a result, the vaquita population has now shrunk to around 10 individuals, down from around 600 in 1997. To better understand the genetic diversity of the remaining vaquitas, an international team of researchers decided to sequence the entire genome of 20 animals from which samples of body tissues were collected between 1985 and 2017. Like humans, vaquitas have two versions of most genes, one inherited from each of their parents. By looking at how often the two versions were identical in animals sampled in different years, scientists were able to estimate how much genetic diversity has changed and how much remains.
Analysis suggests that vaquitas have long been rare. The study estimates that their population size had already fallen below 3,000 individuals more than 25,000 years ago. This means that genetic diversity has been relatively low for a long time, says Jacqueline Robinson of the University of California, San Francisco, one of the study’s lead authors, and the data does not indicate that it has declined significantly. over the past three decades. But is it really encouraging?
Extinction modeling
The fact that the vaquita population has long been low is actually good news, Robinson argues. Over time, many of the worst-performing variants of important genes were likely lost whenever individuals who ended up with two copies of them died prematurely or had no offspring.
“If a much larger population had dropped to 10 individuals over the same period of time,” she explains, “their genetic problems would have been more severe and their chances of extinction much higher.”
Obviously, none of this means that the vaquitas are off the hook. Using the same model that allowed them to estimate past population numbers to predict what might happen in the future, the researchers estimated the likelihood of the species becoming extinct. These figures are of course only approximations, explains Christopher Kyriazis of the University of California, Los Angeles, who led the modeling part of the study. They reflect how often the population disappeared in the model, which was run multiple times.
In scenarios where no more vaquita die in fishing nets, the population survives 94% of the time, leaving a 6% chance that they will still die out. When bycatch mortality was reduced by 90%, the risk of extinction increased to 27%. If deaths were only reduced by 80%, the risk of extinction jumped to 62%.
But reducing the number of bycatch deaths by 90% would mean that a single animal would die in a net roughly every 2.75 years, or every 1.5 years for an 80% reduction, Kyriazis says. To achieve this, there will be an urgent need to prevent the use of gillnets in vaquita habitat, which is long overdue.
A better scenario
So how can this be done?
“Two things have to happen together,” Taylor says. “The first thing has to be: no fishing where the vaquitas are, and then, as quickly as possible, a transition to new gear. It will take government support for that to happen, and in Mexico that hasn’t happened. not been granted to date.
Prohibiting the import of blue shrimp until illegal fishing is eradicated could be another action. “There are ongoing discussions with Mexico about the US-Mexico-Canada trade deal, and I think it’s really important to get honest and authentic information.”
Mexican government officials did not respond to several emails seeking comment from National geographic.
Taylor points out that there is no evidence that the vaquitas are recovering, and it would be a very dangerous time to claim otherwise. But Taylor thinks the new study is good news and the species could still be saved.
“There are other examples of wild populations that have come back from very small numbers. Northern elephant seals were down to around 30, and now they are over 300,000.” vaquitas are more modest, however, with a best-case scenario of 300 individuals by 2070 if no more animals were to die from illegal fishing.
Providing local communities with alternatives to gillnets will be crucial, says Píndaro Díaz-Jaimes of the Universidad Nacional Autónoma de Mexico. He points out that other measures, such as ending the export of totoaba to China, will require international cooperation. In a letter to Science in August 2021, he called the government’s then-recent decision to scale back efforts to control illegal fishing “Mexico’s latest deathblow to the vaquita”. Still, he thinks the new study gives reason for hope.
“I’m a bit more pessimistic,” says marine biologist Mads Peter Heide-Jørgensen of the Greenland Institute of Natural Resources, who studies whale populations in the Arctic. He cites concerns that there may be other issues for very small populations that the model may not fully account for, such as the fact that it may become very difficult for vaquitas to find mates. when only a few individuals remain.
He agrees with the authors that the most pressing issue would be to stop deaths from bycatch, “through the rigorous enforcement of a gillnet ban on primary vaquita habitat. This should have been implemented by the Mexican government long before the vaquita was driven to the brink of extinction.
“These survivors give us a little respite,” says Lorenzo Rojas-Bracho, another co-author, with the United Nations Development Programme, “to change our course towards sustainable fishing.”
This may be the last chance for the vaquitas to catch their breath before becoming entangled in the nets of extinction.
