About 50 mysterious baleen whales live in an underwater canyon off the Florida Panhandle, making them the only resident baleen whales, aka great whales, in the Gulf of Mexico. Several other baleen species visit the Gulf, but these 50 leviathans are the only ones known to live there year-round.

They've long been classified as Bryde's whales — pronounced Brooda's, thanks to 19th-century Norwegian whaler Johan Bryde. Bryde's whales are found in warm seas around the world, growing up to 55 feet long and 90,000 pounds as they feast on plankton, crustaceans and small fish.

But new genetic testing suggests the 50 Gulf whales might be a distinct subspecies of Bryde's — or a new species altogether. If so, they would be "the most endangered species of whale on the planet," says Michael Jasny, director of the marine mammal program at the Natural Resources Defense Council (NRDC), which recently petitioned the U.S. to list the whales as endangered. In April 2015, the National Marine Fisheries Service (NMFS) announced it is considering new protection for the whales.

"The genetics show that these whales are unlike any other of their species," Jasny says. "If anything, they're more related to Bryde's whales in the Pacific than Bryde's whales in the Atlantic. They're different enough to be considered a separate species or subspecies. Then you add to this their difference in size — which appears unique among all Bryde's whales that have been examined — plus their unique calls, and we think we have a very distinctive population in the Gulf."

One of the Gulf of Mexico's 50 "Bryde's whales" is spotted from overhead. (Photo: NOAA Southeast Fisheries Science Center)

Bryde's whales are already enigmatic. It's unclear how many exist, how long they live or whether they're endangered, and there's also confusion about their taxonomy. Scientists didn't distinguish them from Eden's whales until 2003, for example, the same year a "pygmy" Bryde's turned out to be a new species, named Omura's whale. And just last year, researchers identified two subspecies of Bryde's whale.

Not only do the Gulf Bryde's seem like another new species, but their DNA also reveals there used to be a lot more of them. "It's unclear based on the genetics exactly when [the decline] occurred," Jasny says. "It's possible humans were involved in the decline, through whaling or industrial activities. There's a suggestion in the published paper that oil and gas activity might have led to contraction of the range."

That range is now limited to DeSoto Canyon, a chasm off the coasts of Mississippi, Alabama and Florida. Being squeezed into a smaller habitat can hurt any species' genetic diversity, but as Jasny points out, these 50 whale are also still at risk from the region's oil and gas industry. DeSoto Canyon, for example, is adjacent to Mississippi Canyon, where the 2010 Deepwater Horizon oil spill occurred.

"There has been some toxicology work, mainly on sperm whales but also one Bryde's whale that was sampled," Jasny says. "Both showed very high levels of toxic metals that were found in the Deepwater Horizon spill. That study relies mostly on sperm whale tissue samples, but it shows a clear correlation between the toxic load and the proximity of the animal to the spill. And the area in which the Bryde's whales live is unfortunately close enough to be correlated with the high toxic load."

Yet the long-term effects of the BP oil spill, or future spills, are just one potential threat. The Gulf of Mexico has become a loud neighborhood by oceanic standards, thanks to shipping noise as well as the widespread use of seismic "airgun" surveys for oil and gas exploration. Although airguns have been banned in DeSoto Canyon to protect these whales, Jasny worries it can still affect them.

"Sound travels much farther in seawater than it does in air," he says. "We know noise from seismic surveys travels particularly far and can have a large environmental footprint. Great whales are especially vulnerable. We know that airguns can destroy the ability of whales to communicate, hundreds of miles or in some cases even thousands of miles from a single airgun array. We know it causes great whales to cease vocalizing, and that it can compromise their ability to feed. So the fact that airguns are not active within DeSoto Canyon is certainly important, but it hardly eliminates harm to the population."

While truly eliminating harm isn't possible, Jasny and other conservationists hope an endangered species listing could at least minimize it enough to help the whales hang on. The U.S. government already has a backlog of endangered species candidates, though, and these whales will likely need to endure a lengthy waiting period before they get any new protections.

The U.S. Endangered Species Act sets up a timeline for actions on petitions like these, starting with a 90-day review to determine whether the petition offers enough information to support federal protection. That's what prompted the April 2015 announcement by the NMFS, which said it has found "substantial scientific or commercial information indicating that the petitioned action may be warranted."

The next step is recruiting experts to figure out if the population is distinct and whether its problems qualify it as "threatened" or "endangered." After that, federal regulators have one year from the petition date to decide whether to propose the listing, then another year to decide whether to finalize it.

The entire process could take two years, but if regulators end up agreeing with the NRDC, it could yield a federal recovery plan and a protected "critical habitat" in DeSoto Canyon for these 50 whales. If that doesn't happen, though, Jasny warns the population could quietly disappear. "It's hard to imagine how this population — or possibly this species — would survive without protection," he says.