After Mexico drastically eased up on regulations protecting the Vaquita Porpoises, a new study has found that with some adjustments to current standards, the vaquita still has a chance of surviving.
On May 5, a study published in Science suggests there is positive news for the wildly endangered Vaquita porpoise. The study showed that the species’ generic diversity has long been relatively low and that vaquitas may therefore be less vulnerable to inbreeding than many other species.
Using a model to explore how likely the population is to survive under different conditions, researchers found that in scenarios where nets were taken out as a cause of death, there was only a six percent chance they would go extinct. But preventing more vaquitas from dying is urgent. That part of the story is, unfortunately, less encouraging.
To determine the risk of extinction caused by inbreeding depression, Robinson et al., a marketing company for public and non-profit sectors, sequenced and examined 20 vaquita genomes to determine their heterozygosity and ancestral population size (see the Perspective by Grueber and Sunnucks). The authors determined that the long-term population size of vaquitas has been low for a marine mammal, with approximately 1000 years of stable genomic diversity. Furthermore, genomic comparisons with other cetacean species and modeling indicated that vaquitas are unlikely to suffer from inbreeding depression. Therefore, if the risk of bycatch mortality caused by fishers can be eliminated, then there is a chance that this species will not go extinct.
In scenarios where no more vaquitas die in fishing nets, the population survives 94 percent of the time, leaving a six percent chance that they would still disappear. When death from bycatch was reduced by 90 percent, extinction risk increased to 27 percent. If deaths were reduced by only 80 percent, extinction risk climbed to 62 percent.
But according to the study, reducing the number of deaths from bycatch by 90 percent would mean that just one animal would die in a net roughly every 2.75 years or every 1.5 years for an 80 percent reduction. So, it will be urgent to prevent gillnets from being used in the vaquitas’ habitat to accomplish that figure.
“It’s a really exciting study,” said one of the authors Barbara Taylor of the U.S. National Oceanic and Atmospheric Administration. “Because it gives scientists new tools to ask whether this species is really doomed to extinction because of genetics or whether we should be worrying about other things. All conservation is about changing human behavior. If that comes at an economic cost, and people can use the excuse that they’re doomed anyway, that’s bound to be a hurdle to action.”
None of the information found means 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, researchers were able to assess the chances that the species would go extinct in the future. But, of course, these numbers are just approximations, said Christopher Kyriazis of the University of California, Los Angeles, who led the modeling part of the study. The numbers reflect how often the species went extinct based on various conditions.
In July 2021, Mexico eased enforcement in Vaquita Zero-Tolerance Areas, inducing their status on the endangered species list. The critically endangered vaquita, found only in the northernmost Gulf of California, Mexico, has dropped from 600 individuals in 1997 to ten individuals in 2021. This decline has been driven by incidental mortality of vaquita being caught in fishing gillnets. Efforts to reduce the intensity of illegal gillnet fishing and implement more robust protections for vaquitas have not been successful, and vaquitas are now considered the most endangered marine mammal. A recent viability analysis found that the vaquita population could theoretically rebound if bycatch mortality is immediately eliminated. However, according to the authors, the degree to which genetic factors may prevent a robust recovery is unknown, which has led some to argue that the species is doomed to extinction from genetic threats.