The elusive vaquita porpoises 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 them left in the wild.
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.
“Based on the uncertainty inherent in the models, the number could be as few as six,” said Prof Len Thomas, a statistician at the University of St Andrews and an author on the study.
The vaquita population lives in an area at the upper corner of the Gulf of California in Mexico. To estimate their numbers, the researchers recorded the vaquitas’ echolocation clicks using a large grid of acoustic sensors stationed over their habitat. Combined with visual sightings, the data shows a decline of 98.6% since monitoring started in 2011.
According to the study, published in the 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 critically endangered species get caught and drowned as a bycatch in gillnets. These nets are vertically suspended in water and the spacing of the mesh is supposed to allow only fish of certain size to be caught, but in practice marine mammals and sea turtles can quickly become entangled and drown.
The critically endangered species get caught in walls of netting (called gillnets) that 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.
Dr Peter Evans, an honorary senior lecturer at Bangor University who was not involved in the study, said: “This paper by a group of very reputable scientists graphically demonstrates the precarious situation for [vaquita], with less than 20 estimated to remain on this planet.
“It is just possible that some individuals may have escaped notice in areas outside the core study area, and there are challenges in determining numbers from porpoise echolocation detection’s. However, the authors have done their very best to try to overcome these in the analyses conducted in the paper. The only way to save the species would be to ban fishing of this type in the Gulf of California.”
Thomas added: “We only have about a year left to save [the vaquita] from going extinct. The good news is that it’s a simple solution. With enough resources the Mexican government could protect them by cracking down on illegal fishing nets. We’re talking about an area less than the size of Greater London.
“The Mexican navy is perfectly capable of excluding those boats from the area. My hope is that through publicity we will inspire the Mexican government to undertake effective enforcement.”
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.