Extreme tide changes may have doomed pilot whales stranded off the coast of Florida, a marine mammal expert suspects.

Nearly a week ago, 51 pilot whales were spotted in the waters off of Everglades National Park. Last week, 11 died and 5 were unaccounted for, but the rest were herded away from land by rescue teams in boats. As of today, however, the situation appears to be more bleak.

During a press conference Monday afternoon, NOAA spokesperson Blair Mase said 22 pilot whales have now died and the other 29 remain unaccounted for and could be dead as well. Necropsy results are forthcoming.

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Pilot whales can contract morbillivirus, a sometimes-fatal illness in other cetaceans. The virus is in the same genus as that which causes measles in humans.

Mase said there are reports of red tide happening along the southwest Florida coast. That’s when algal blooms produce toxins, deplete water of dissolved oxygen, and turn water a reddish hue. As of now, however, she doesn’t suspect that affected the whales.

Phillip Clapham, leader of the Cetacean Assessment and Ecology Program at the National Marine Mammal Laboratory, believes other factors are involved.

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“Pilot whales are an offshore species and are probably less experienced with shallow coastal waters,” Clapham told Discovery News. “These strandings are not uncommon, and they often occur in the same places. While we can’t explain every stranding, or even say exactly why a particular stranding happened, there are clearly a set of factors involved, and every time you throw one more factor into the pot you increase the chances of a stranding.”

He continued, “The general scenario is likely something along the following lines: Pilot whales come into one of these areas to feed on a high tide, then suddenly the tide drops and they find themselves trapped in a maze of shallows. That in itself is enough to cause a stranding, but if you also throw in bad weather then it makes things much worse… whales are in a maze of sand flats and shallows, with the wind and waves kicking up sediment into the water, making it even harder for them to orient themselves and sometimes with waves pushing them onto a beach.”

He added, “The social cohesion of the group is another factor; many pilot whale groups consist of relatives, and if one gets into trouble, the others probably follow.”

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Clapham suspects this particular pod became stranded on or close to December 3, during the extreme tidal changes associated with the new moon of that period.

If you find a beached or stranded marine mammal, please report it as soon as possible to local authorities. NOAA Fisheries has organized the Marine Mammal Stranding Network, which lists offices to contact.

Image credit: NOAA Fisheries