Eleven more pilot whales were found dead in the lower Florida Keys on Sunday, believed to be from a pod of 51 that became stranded there last week, and authorities said chances were slim of finding the remaining whales alive.
The pod of 51 short-finned pilot whales were first observed stranded on the edge of the Florida Everglades National Park on Tuesday. Despite frantic rescue efforts by scientists, ten of the whales died on Wednesday and another on Thursday.
With the 11 whales found dead on Sunday, about six miles north of Sugar Loaf Key, a total of 22 have been confirmed dead, the U.S. Coast Guard said in a written statement.
The Coast Guard said 29 whales remained missing, having last been seen alive on Friday.
"Given our knowledge of past mass pilot whales strandings, the outlook for finding the remaining whales alive is bleak," the Coast Guard said, adding that other whales may have already died and their bodies sunk under water.
Experts have so far not offered an explanation for why the whales were beaching themselves and dying in the Florida Keys.
Scientists were expected to take samples from the 11 whales found on Sunday to determine a cause of death, including possible biotoxins or "red tide."
The Coast Guard said there was no evidence of sonar trauma but that it had made inquiries with the U.S. Navy.
The dead whales have included both males and females and have had empty stomachs, suggested their health may have been compromised prior to the beaching.
Scientists have performed necropsies on the first 11 deceased whales to look for possible diseases and pathogens as well as environmental and human causes, but results may not be available for at least several weeks, the Coast Guard said.
Pilot whales are social, living in pods of 20 to 90, and typically will not leave ailing or dead members behind. They are a deep-water species that forages on squid, octopus and fish and cannot live long in shallow water.
The rescue team includes National Oceanic and Atmospheric Administration Marine Fisheries Service, U.S. National Park Service, Florida Fish and Wildlife Conservation Commission, Marine Mammal Conservancy, Marine Animal Rescue Society, and U.S. Coast Guard.