Inbreeding won’t doom the last of the vaquitas, but fishing might: study

Washington - Vaquita porpoises are on the edge of extinction, with just 10 left in their sole habitat within Mexico’s Gulf of California. However, a new study published Thursday in the journal Science offers some hope: the world’s rarest marine mammals aren’t doomed by a lack of genetic diversity, and can recover if illegal “gillnet” fishing ceases immediately. “We’re trying to push back on this idea that there’s no hope, that nothing we do could save them at this point. It’s just not an accurate assumption,” lead author Jacqueline Robinson of the University of California San Francisco told AFP. Porpoises are closely related to dolphins, and share many things in common including great intelligence. The vaquita, whose name means “little cow” in Spanish, measures four to five feet (about 1.5 meters) in length, making it the smallest of all cetaceans. Shy and elusive, they are known for distinctive dark circles around their eyes, and relatively large dorsal fins, which are thought to help them dissipate heat in their warm habitat. Vaquita numbers were decimated in the 20th century as a result of being accidentally trapped and drowning in gillnets: long walls of nets hanging in open water that are used to catch fish and shrimp. Fishermen sought in particular the totoaba, a large fish about the size of the vaquita, whose swim-bladder is prized in traditional Chinese medicine. The totoaba itself is endangered and its fishing is illegal, but the ban isn’t always respected. The vaquita’s historical abundance was unknown, but by the time of the first survey, in 1997, only around 570 remained.There were fears that harmful mutations among the surviving vaquitas could seal the species’ fate due to inevitable inbreeding. To find out whether that was the case, the researchers analyzed the genomes of 20 vaquitas that lived between 1985 and 2017, and discovered that over the past 250,000 years their population had never exceeded a few thousand. They also learned that their genetic diversity had always been low, relative to other cetacean species such as dolphins, orcas, and other whales.

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