Genetic analysis and a close examination of the skulls from a group of baleen whales in the north-eastern Gulf of Mexico have revealed that they are a new species. “I was surprised that there could be an unrecognized species of whale out there, especially in our backyard,” says Lynsey Wilcox, a geneticist with the US National Oceanic and Atmospheric Administration who helped uncover the new species. “I never imagined I would be describing a new species in my career, so it is a very exciting discovery.” The newly described whales weren’t exactly hiding in plain sight. With a population estimated at fewer than 100, the new whales – which researchers have dubbed Rice’s whales after American biologist Dale Rice – aren’t commonly seen even in the corner of the Gulf of Mexico they call home. It doesn’t help that the whales, previously believed to be a population of Bryde’s whales, have a feeding strategy that takes them deep under the water around DeSoto Canyon, about 100km south of Mobile, Alabama. Researchers have long known that this group of Bryde’s-like whales in the Gulf of Mexico was different. They seemed to mostly stay put in the north-eastern corner of the gulf, and didn’t mingle with Bryde’s whales, which are found in the Indian, Atlantic and Pacific Oceans. They also feed near the seafloor, while most Bryde’s whales typically forage near the surface. But it’s difficult even for experts to tell large baleen whales apart in the field – so much so that Bryde’s whales sometimes get confused with fin whales, says John Hildebrand, a biological oceanographer at Scripps Institution of Oceanography at the University of California San Diego who was not involved in the recent study. To definitively tell similar-looking species apart, scientists need genetic evidence and a close examination of the animal’s morphology, Wilcox says. Wilcox’s colleagues first began collecting tissue samples from Rice’s whales in 2000, eventually collecting samples from 36 different individuals. Comparing their genes with Bryde’s whales, Wilcox says she and her colleagues “noticed that they weren’t quite what was expected”. To compare their morphologies, the scientists inspected skeletons held in museums. Then, in January 2019, an 11-meter-long Rice’s whale washed up on a key in the Florida Everglades. Examining the whales’ skulls revealed some differences in the shape and size of the bone material around the blowhole compared with Bryde’s whales and Eden’s whales, another close cousin. The genetic and skeletal differences together were enough to warrant a new species designation, Wilcox says. Hildebrand agrees that this “uniquely American whale” should be recognized as a new species. While normally some researchers might want to see the genes of more individuals than the three dozen examined by Wilcox and her colleagues, Hildebrand says that isn’t practical considering how few Rice’s whales there are. “This paper is the best we can do right now to demonstrate that they are different – it’s perfectly adequate,” he says. Rice’s whales are already considered endangered by the United States. They were listed under the Endangered Species Act as a population of Bryde’s whales in April 2019, and the discovery that they are a distinct species is unlikely to change much – other than requiring an update of their name. Living in the Gulf of Mexico, the whales face threats from oil spills, ship strikes, ocean noise and entanglement in fishing gear. Hildebrand says the whales are particularly vulnerable to ship strikes because they have the “unfortunate habit” of sleeping at night just under the sea’s surface. “At night you wouldn’t see them,” he says. “A ship traveling past could come right up and hit them.” Hildebrand speculates that the whales might once have been more widespread in areas with deeper water, but they are now holing up in an area that sees less ship traffic. “They are the most endangered, or nearly the most endangered, baleen whales in US waters,” Hildebrand says. “In terms of the responsibility for the health of the whale, it really does fall on us.”