There are now just 10 vaquita porpoises remaining on the planet, yet new research demonstrates that this critically endangered marine mammal could still recover if gillnet fishing is immediately halted in the Gulf of California. Appearing in the journal Science, the new study suggests that despite dwindling numbers, this rare creature isn’t at risk of entering an “extinction vortex” due to inbreeding.
Native to the shallow waters off the coast of northwest Mexico, the vaquita is among the world’s most endangered animals, largely thanks to the illegal use of gillnets within its natural habitat. While the nets are often intended to catch a threatened fish called totoaba – valuable for their supposed medicinal properties – vaquitas often become trapped in the equipment as bycatch and drown.
The decimation of the population had led to fears that vaquitas may become genetically compromised due to inbreeding, thus hastening their decline and dooming them to extinction. However, the study authors found that this is not the case and that the removal of human pressures could enable numbers to rebound.
The researchers reached this conclusion after analyzing the genomes of 20 vaquitas that lived between 1985 and 2017. Results indicated that the species carries fewer harmful mutations than other marine mammals, which means that even if inbreeding occurs, offspring are unlikely to inherit negative traits that could compromise their health.
Usually, genetic variation ensures that a certain number of deleterious mutations lurk within a population, though these are typically expressed as traits only when two individuals carrying the same mutation mate. In large populations, this is rare but becomes increasingly likely as numbers decline and inbreeding occurs more frequently.
Vaquitas, however, have always existed in small numbers, thus ensuring a low amount of genetic variation. As a result, few of these potentially hazardous genetic variants exist within the species’ genome, thus decreasing the prospect of the phenomenon known as inbreeding depression.
“They’re essentially the marine equivalent of an island species,” said study lead author Jacqueline Robinson in a statement. “The vaquitas’ naturally low abundance has allowed them to gradually purge highly deleterious recessive gene variants that might negatively affect their health under inbreeding.”
Based on their genetic analysis, the researchers simulated future vaquita population changes under various fishing scenarios. They found that if gillnet fishing were to cease overnight, only 6 percent of vaquitas would die off due to inbreeding depression over the next 50 years, allowing numbers to rebound to 299 individuals by 2070.
However, if just 10 percent of gillnet bycatch mortality continues, vaquita populations would decline by 27 percent in the next half-century, while extinction rates would increase to 62 percent if 20 percent of gillnet killings are allowed to persist.
“The survival of the individuals, and the species, is in our hands,” said study author Phillip Morin. “There is a high probability genetically that they can recover, if we protect them from gillnets and allow the species to recover as soon as possible to historical numbers.”