In the largest recorded stranding of false killer whales in Florida history, at least 81 of the large black dolphins died after they became trapped over the weekend near a mangrove-filled shoreline in the Gulf of Mexico.
Officials are trying to determine why the pod of about 100 dolphins swam into the shallow waters on the western edge of Everglades National Park, where some became caught in mangroves tangled along the shore. Rescue crews are also searching for the dozen or more additional dolphins also believed to have become stranded, according to Blair Mase of the National Oceanic and Atmospheric Administration’s Marine Fisheries Service.
Little is known about false killer whales, the fourth-largest member of the dolphin family, which live in warm, deep waters in all three major oceans. Strandings of false killer whales have happened before, with the largest occurring in 1946 when an estimated 835 became stranded near an Argentinean beach.
As their name suggests, false killer whales resemble orcas at a distance, but they lack the characteristic white oval that encircles the eye of their larger cousin. The black-and-grey dolphin has a small conical head without a beak, a tall dorsal fin, and flippers (pectoral fins) with a distinctive bulge.
The pod of dolphins beached in Florida was first spotted on Saturday in a remote site near Hog Key, a stretch of the mainland that sits amid a dense network of islands off southwest Florida, according to the Miami Herald. After the Coast Guard confirmed the sighting of the black dolphins, efforts to herd the mammals into deeper waters failed on Saturday and Sunday, Ms. Mase of NOAA told reporters.
The dolphins – in a group which included adults, juveniles, and calves – were “deeply embedded in some of the mangroves, making response efforts extremely difficult,” Mase told the Herald. Rescuers ended up euthanizing nine dolphins too sick to survive, while 72 died on their own by Sunday, said Mase.
Because of insufficient data, it is unknown how many false killer whales there are worldwide, according to the IUCN Red List, one of the most comprehensive databases of the conservation status of animal and plant species. Pods in the northern Gulf of Mexico number 1,038, according to a 2004 study that IUCN cites.
IUCN also cites a 2006 study that found that false killer whales, like beaked whales, are “likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration.”
As NOAA plans to study samples of the dead dolphins to determine why they swam ashore, previous strandings offer different clues.
In 2013, 30 of the dolphins beached themselves in shallow sands in northeastern Brazil, halfway between the cities of Fortaleza and Natal. At the time, Brazilian newspaper O Globo reported it was not known why the animals stranded themselves, but biologists were considering whether the pod leader might have been incapacitated. Another hypothesis was that the dolphins were pursuing a school of fish when they became trapped on Upanema beach’s high sand banks.
The year before, more than 177 short-beaked common dolphins were stranded on Cape Cod in Massachusetts, of whom 53 survived. Scientists didn’t have an answer for those beachings either.
Strandings of false killer whales are rare in the US, with the last occurring in 1986 when a pod of 40 swam close to Cedar Key, Florida, according to Mase. But larger strandings, involving pods of more than 100 dolphins, have occurred in Australia and South America.
This weekend’s beaching occurred months after a federal court ruled against the US Navy testing certain low-frequency sonar because, the court found, it could affect dolphins, whales, and other marine mammals that rely on the sound generation.
Conservationists have fought the Navy’s use of sonar and explosive testing for years because, they argue, it interferes with marine mammals’ migration and communication patterns, as well as their ability to find feeding and breeding locations.
This report contains material from the Associated Press and Reuters.