Wildlife Week 2019: Just 19 of the most endangered mammal, the vaquita porpoise, still swim in the wild

There are fewer than 19 vaquita porpoises, the most endangered mammal, to still exist in the wild, according to a new survey by a university in Scotland. The threat to their survival continues to come from illegal use of fishing nets in the Gulf of California, Mexico.

The upper Gulf of California is now the only remaining home of the vaquita porpoises, whose numbers have dropped to fewer than 10, according to the new research by the University of St Andrews. The study is published in the Royal Society Open Science.

A pair of vaquita porpoises swimming in the Gulf of California, Mexico. Image: Geographic NZ

Using a technique called echolocation, which uses large grids of sound sensors spread out over the water's surface, the vaquita's "clicks" were recorded by researchers, identified and used to estimate the number of individuals still inhabiting the Gulf. Their numbers have seen a sharp declined – nearly 99 percent – since the monitoring study began in 2011, and by almost 50 percent every subsequent year since 2016, the statement claims.

One of the biological disadvantages of the vaquitas is their long reproduction cycle, which means they can't reproduce quickly. They reach sexual maturity at three to five years of age, and have a gestation period (a pregnancy, carried to term) lasting 11 months on average. Scientists believe that the vaquita could soon go extinct because its genetic pool – the mix of genes and variations in genes that exist in a population – is far too small for them to reproduce in a healthy manner. Much like in human populations, mating with blood relatives can result in children that are more prone to disabilities and unfit in the context of survival. This is true not just for humans and vaquitas, but all mammals, and doesn't bode well for the dozen or so vaquita porpoises still in the wild.

A vaquita, which translates to "small cow" in Spanish, looks a lot like a dolphin. These animals are the world's smallest cetaceans, have gray or white bodies, long flippers and a tall dorsal fin. Globally, their population was estimated at 30 in 2016. The use of gillnets for fishing, which hang vertically and catch fish by their gills, have wiped out half the vaquita population as a bycatch. Mexico has long since banned the use of gillnets, and yet the illegal fishing practice appears to be continuing.

"The ongoing presence of illegal gillnets despite the emergency ban continues to drive the vaquita towards extinction. Immediate management action is required if the species is to be saved," Professor Len Thomas, director of the University's Ecological and Environmental Modelling division, said in a statement.

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