How whales lose their way: Toxins, tides and other troubles

Pilot whales move to deeper water 1:38

How did dozens of pilot whales get so seriously stranded in Florida's Everglades National Park? This week's marine mammal drama raises questions about the peculiar biology and sociology of short-finned pilot whales, as well as factors ranging from disease outbreaks to astronomy.

How common is it to have wayward whales?
"These sorts of strandings with pilot whales are not uncommon," said Phillip Clapham, who heads the Cetacean Assessment and Ecology Program at the National Marine Mammal Laboratory in Seattle. The most recent whale stranding in the Everglades was back in 1995, but about 20 whales were beached elsewhere on the Florida coast in 2011, and again last year.

This time around, 51 whales wound up stranded: As of Thursday afternoon, 11 whales were found dead or had to be euthanized. About 35 were alive and making their way offshore, said Blair Mase, a fisheries stranding coordinator for the National Oceanic and Atmospheric Administration. She said that left about five missing whales. At least some of those whales may have died and sunk beneath the surface. 

What causes the whales to lose their way?
Lots of factors can play a part. "Every time you throw in one more element, you increase the chance of stranding," Clapham said.

For example, researchers say parasites or infections can confuse the whales' sense of navigation. Pilot whales can suffer from morbillivirus, a strain that's related to the virus implicated in this year's dolphin die-off. Clapham doubts that virus caused this week's strandings. Nevertheless, biologists in Florida have taken tissue samples from the 11 dead whales, and they'll be studying those samples for signs of toxins over the weeks and months ahead.

Human activity has the potential to confuse whales as well — perhaps through sonar or seismic disruptions, or interaction with fisheries. Those causes also seem unlikely in the Everglades case. The most likely factors are environmental: shifts in currents, changes in the underwater terrain, a turnabout in the weather, or perhaps the influence of tides.

Tides? Really?
High moon tides, also known as "spring tides," are known to be problematic for pilot whales. And a spring tide occurred early Tuesday, on the day when the whale stranding was first observed. "Suddenly the tide goes out, and the whales find themselves trapped in a maze of shallows," Clapham said. He said he and his colleagues accurately predicted a couple of whale strandings in Massachusetts' Cape Cod, based merely on the tide tables and weather forecasts.

NOAA's Mase acknowledged that tides can play a part in whale strandings, particularly in the Northeast, but told NBC News that "we don't believe that tides are a factor in this event."

Why is it so hard for the whales to get out?
The Everglades situation is particularly tricky, because the whales have to make their way through a long stretch of sand flats and shallow water. "We're herding animals miles and miles, at least trying to give them a shot to go out into deeper water. ... There's literally 10 to 15 miles to get into significantly deeper water," Mase said.

Can't the whales just be scooped up and moved?
The logistics for moving the whales forcibly for such a long distance are unworkable — and even if it were workable, such an operation would put severe stress on the animals. Mase said the NOAA-led rescue team was relieved to see that the whales were heading farther offshore on Thursday afternoon, although they still have several miles to go. "We are encouraged and hopeful, but there's no guarantee that they will continue offshore," she said.

How can so many whales get into so much trouble together?
Pilot whales are an exceptionally social species, and they're reluctant to leave their podmates behind. "If one animal gets into trouble, they all get into trouble," Clapham said. That explains why it was so difficult for rescuers to herd the dozens of live whales away from the dead ones on Wednesday.

Clapham noted that short-finned pilot whales (and orcas, also known as killer whales) are among the relatively few species that experience menopause as humans do. "It's kind of like keeping Grandma around because she knows where the food is," he said. Other researchers have suggested that the granny whales also help mothers care for their offspring.

More about whales:

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding +Alan Boyle to your Google+ circles. To keep up with's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.