But according to a new study, this does not yet mean the death of vaquita porpoises.
Vaquitas are on the brink of extinction due to illegal gillnet fishing, which is used to catch shrimp and totoaba fish that share the same habitat as porpoises. Vaquitas 4 to 5 feet (1.2 to 1.5 meters) long become “bycatch” as they are not the intended target of the nets.
The totoaba fish, whose status is Vulnerable on the International Union for Conservation of Nature’s Red List of Threatened Species, has a swim bladder that is prized in China and used in traditional medicine – and even seen as a financial investment. In Mexico, totoaba fishing is outlawed and gillnet fishing is banned where the vaquita live, but the practice continues unabated.
With such a small population, the researchers wondered if vaquitas were at greater risk of extinction due to inbreeding.
Now a team of scientists including Taylor and Rojas-Bracho have studied the genetic patterns of vaquita tissue samples collected between 1985 and 2017 by Mexican researchers. Taylor is a Senior Scientist at the Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center in La Jolla, California, and Rojas-Bracho is a conservation biologist and member of the National Commission on Protected Areas in Mexico.
“Who would have thought that a few decades later, the same samples could tell us so much,” study co-author Rojas-Bracho said in a statement. “Genomics gives us clues to the past species, but also allows us to look into the future.”
“If we let these animals survive, they can do the rest,” said study co-author Jacqueline Robinson, a postdoctoral fellow at the University of California, San Francisco. “Genetically, they still have the diversity that allowed them to thrive for hundreds of thousands of years before gillnets evolved.”
Small but thriving
Genetic information from vaquitas shows that they appeared about 2.5 million years ago and adapted to life in the shallow waters of the northern Gulf of California.
Over the past 250,000 years, the population has ranged from a few thousand to about 5,000 vaquita, which is rare compared to other marine mammals. The fact that they have maintained a small population for so long has helped reduce the risk of inbreeding because there are fewer genetic differences between them. A comprehensive survey of the population in 1997 showed that there were 570 porpoises, but this number has decreased significantly over the past 25 years.
Vaquitas also experience less dangerous genetic mutations associated with small populations. When animals with negative genetic traits mate, their offspring are more likely to die.
In the case of this population, it actually helped eliminate harmful traits from spreading through the vaquita population.
“It’s basically the marine equivalent of an island species,” Robinson said. “The vaquita’s naturally low abundance has allowed them to progressively shed very detrimental recessive gene variants that can negatively impact their health when inbreeding.”
Variants rarely appear in large animal populations because it is unlikely that two animals with such traits will find each other and mate. But when the population declines rapidly, those chances increase and their offspring experience “inbreeding depression”. This weakens their health and can lead to the extinction of the species.
“The prevailing view in conservation biology and population genetics is that small populations can accumulate deleterious mutations,” senior study author Kirk Lohmuller, assistant professor of ecology, evolutionary biology, and human genetics at the University of California, Los Angeles, said in a statement. .
“However, our finding that vaquitas likely have fewer highly detrimental mutations latent in the population means they are better prepared for future inbreeding, which bodes well for their overall recovery.”
How to save them
Gillnets pose the greatest threat because they drown porpoises.
The researchers ran simulations based on genetic information from vaquitas to see which scenario would best protect them and calculate their risk of extinction over the next 50 years.
Immediate removal of gillnets from their habitat was the best option for vaquita survival. Unfortunately, even modest use of gillnets can reduce their chances of rebounding. According to the study, if vaquita mortality as bycatch is reduced by 80%, 62% of the population could still go extinct.
“The survival of individuals and species is in our hands. Genetically, there is a high probability that they can recover if we protect them from gillnets and allow the species to recover to historical abundance as soon as possible, ”the study says. co-author Philip Morin, molecular research geneticist at NOAA’s Southwest Fisheries Science Center, in a statement.
Studies have also been done to monitor some of the few remaining vaquitas, and the researchers were happy to see that they look healthy and even have young swimming with them, which means they are actively breeding.
“We have very little time left,” study co-author Christopher Kyriazis, a doctoral student in ecology and evolutionary biology at the University of California, Los Angeles, said in a statement. “If we lose them, it will be the result of our human choices, not innate genetic factors.”
Scientists continue to actively monitor vaquitas. The researchers believe their approach to this study could be used to predict the extinction risk of other endangered species based on their genetics.