Illegal fishing and deadly poaching nets remain the biggest threat despite the limited population size.

We’ve known for some time that the vaquita – the world’s smallest marine mammal – dangles on the brink of extinction. There are currently only 10 copies alive. You would therefore say that the vaquita no longer stands a chance. Because normally such a small population size and limited genetic diversity would cause a species to become extinct. Yet it appears from a new study that inbreeding isn’t even the biggest problem for the vaquita. Because if we can prevent them from getting entangled in poaching nets, they have a remarkably good chance of survival.

inbred

In the study, the researchers analyzed the genomes of 20 vaquitas that lived between 1985 and 2017. They then ran computer simulations to predict the species’ extinction risk over the next 50 years. Remarkably, the analysis shows that limited genetic diversity and inbreeding do not really seem to get in the way of the species. “Compared to other species, the vaquita has a greater chance of recovering from an extreme population decline,” said study researcher Jacqueline Robinson. “The genetic diversity in vaquitas is not so low as to pose a threat to their health and survival. It just reflects their natural rarity.”

Small population

It’s an interesting discovery. Indeed, the prevailing view is that harmful mutations can accumulate in small populations. But the vaquita probably possesses fewer harmful mutations, meaning they are better able to survive future inbreeding. And that bodes well for their recovery.

What exactly protects the vaquita from the genetic dangers of inbreeding? This is mainly due to the fact that they have always existed in small populations. In addition, the critically endangered vaquita is only found in a small area, namely in shallow lagoons in and around the Colorado Delta in the northern Gulf of California. And here the harbor porpoise has been able to survive in small numbers for hundreds of thousands of years. Although their historical numbers are unknown, the first comprehensive survey in 1997 counted about 570 vaquitas—a number that has steadily declined over the past 25 years, but was not large at first.

“Vaquitas are essentially the marine equivalent of an island species,” Robinson sums up. “The species has survived for tens of thousands of years with low genetic diversity. The naturally small population size has subsequently allowed them to gradually purge highly harmful gene variants that could negatively affect their health through inbreeding.”

Illegal fishing

Although there are only 10 vaquitas alive worldwide, inbreeding is not the biggest problem that the species has to overcome. The vaquita is not doomed to extinction due to genetic factors. So what is their biggest threat? “Illegal fishing,” underlines researcher Christopher Kyriazis.

gillnets

The small porpoises, which are between 1.2 and 1.5 meters in length, unfortunately often become entangled in gill laws. These are nets in which a fish can put its head through a mesh of a net, but cannot get out because it then gets stuck behind the gill covers.

Gillnets are used by fishermen who hunt the totoaba, another endangered species. The Mexican government banned use of the nets in the northern Gulf of California in 2017, but poachers continue the practice illegally. Image: iStock.com/Damocean via UCLA

These nets are used by poachers to Totoaba macdonaldic to hunt, which occurs in the same habitat as the vaquita. Poachers prey on this species because of the swim bladder of this fish, which sells for tens of thousands of dollars on the black market in China. But at the same time, the same nets have entangled and killed thousands of vaquitas in recent years, probably leaving only a few animals swimming around. Although Mexico has banned the hunting of totoaba and the use of the nets in the vaquitas’ habitat has become illegal, many say the bans are not always enforced.

recovery

The researchers conclude that if illegal gillnet fishing stops immediately, the vaquita has a very high chance of recovery, even with the threat of inbreeding. If the fishery continues, however, the prospects for recovery are much less optimistic. If no further measures are taken to protect the porpoises, there is a good chance that they will become extinct. “The loss would be a great tragedy,” said researcher Robert Wayne. “The vaquita symbolizes the unique diversity we find in the Gulf of California. It represents a unique evolutionary lineage – there is no comparable species anywhere in the world – and its loss would rob the ecosystem of an important animal adapted to this unique ecosystem.”

While the number of vaquitas can be counted on two hands, the current study shows that it doesn’t necessarily mean their downfall. “The species’ ability to recover is not limited by their genetics,” concludes Kyriazis. “If they do go extinct, it would be the result of our human choices, not inherent genetic factors.”