The vaquita has the unenviable distinction of being the rarest marine animal on the planet – and a new study estimates there could be fewer than 19 of the elusive porpoises left.
Scientists have been tracking vaquita activity since 2011 to estimate population numbers, using sightings and clicks to make their calculations. Because the cetaceans use clicks to echolocate and communicate on an almost constant basis, the number of clicks collected by the team's underwater sensors over a 62-day period (June 19 to August 19) can be used to work out year-on-year fluctuations in population numbers.
According to the study, published today in Royal Society Open Science, the average number of clicks detected each day fell by 62.3 percent from 2016 to 2017 and a further 70.1 percent from 2017 to 2018. What's more, the researchers say there is 99 percent certainty that vaquita numbers have declined 98.6 percent since tracking began in 2011.
The study backs up previous reports highlighting dramatic population decline – even if the exact numbers vary. In 2014, it was announced that vaquita numbers had dropped below 100 for the first time. By 2017, there were thought to be just 30 of the porpoises left. That figure fell to 12 in 2018 and a report earlier this year found there were only 10 vaquitas remaining.
The study authors suggest that some of these figures may be influenced by sampling error or some negative statistical bias. They estimate that there were around 100 vaquitas in 2015, higher than the 60 previously reported.
Regardless, the numbers suggest that if nothing is done soon, the smallest cetacean in the world could soon go the way of the Yangtze river dolphin, or baiji, which is thought to have gone extinct sometime around 2006 despite some unconfirmed sightings more recently.
Vaquita distribution is thought to be limited to a small strip in the Gulf of California's northern tip, near Mexico. Despite the Mexican government's efforts to enforce a Vaquita Refuge Area, the animal continues to face threats from illegal fishing practice – not because they themselves are prized, but because they just so happen to share a habitat with a fish that is.
The (also critically endangered) totoaba fish is a valuable commodity in China where they are appreciated for their supposed "medicinal" properties and can fetch upwards of thousands of dollars on the black market.
Walls of netting (called gillnets) have been declared illegal in the Gulf of California since March 2015 but fishers regularly flout the ban and install the nets to catch totoaba fish. These nets are indiscriminate and vaquitas are collateral damage. According to the study, eight of the 10 dead vaquitas found since 2016 died as a result of these gillnets. Cause of death could not be determined for the remaining two.
While the study estimates there were fewer than 19 vaquitas left as of August 2018 – and admits this number could be as low as six, if we consider sightings alone – the authors are not without hope. Research carried out in September 2018 found the remaining individuals in good health and with two calves, suggesting there is evidence vaquitas could calve annually.
"This finding gives optimism for recovery if the killing could be halted immediately," the authors write.