Gray whales stop off to feast on shrimp during high tide on the mudflats.

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More gray whales are risking their lives for shrimp cocktail

HALIFAX, CANADA—Among cetaceans, gray whales are the curmudgeons: They’re often reclusive and set in their ways, spending much of their time nosing alone along the Arctic Ocean bottom for tasty invertebrates. But a dozen gray whales along the coast of Washington state are showing that even loners can get social. Using special suction cup tags with cameras and sensors—plus high-resolution satellite images from Google Earth—marine biologists have found that a small party of whales has started detouring 200 kilometers to feast on ghost shrimp during their annual northward migration—and that the party is getting bigger all the time. That behavior reveals that even gray whales can learn new tricks from their companions, the scientists say.

Perhaps the biggest surprise was that the whales are spending “a lot” of time together, said John Calambokidis, a marine mammal researcher at the Cascadia Research Collective in Olympia, here at this week’s biennial meeting of the Society for Marine Mammalogy.

Calambokidis and others have been logging the whales’ visits since two showed up in 1991 in the delta of the Snohomish River that feeds into Puget Sound; by 2015 there were a dozen. At least one—a female they’ve dubbed Earhart after the famous aviator—has been coming year after year. These whales spend about 3 months hanging out in the delta, Calambokidis explained, despite the risk of being stranded. Over time, they have attracted whale watchers and ignited the concerns of local fishermen, who also harvest the 7-centimeter, whitish ghost shrimp for live bait. The shrimp spend most of their lives in complex burrows that require just the right mix of sand and mud.

To find out exactly what was going on, the team outfitted 11 whales with suction cup tags that included a camera, a motion detector, and a depth sounder. They collected 130 hours of video, with one tag lasting 67 hours before falling off. One video showed that as three so-called “sounders” (named after a local soccer team) came into the delta on the rising tide, they jostled one another and tailed Earhart so closely that they knocked her video camera around to face backward. Once they reached the mudflats, they put their heads down in about 2 meters of water and stirred up the sediment, sucking in both grit and thousands of ghost shrimp in one great, easy gulp. Hours later, they escaped back to the deeper water as the tide ebbed. There, the whales—not known for such collegiality—hang out together on the bottom, waiting for the next high tide.

While working on another project, Cascadia marine biologist Nathan Harrison realized he could see where the whales excavated food in the mudflats—thanks to satellite images from Google Earth, in which their feeding pits appear as dark blotches. He scoured Google archives and found 10 days in which the tide was low enough to make out the 2-meter-by-1-meter depressions left by the whales. He counted up to 19,447 such pits. “To be able to use satellite images that were not collected for that purpose for scientific research is amazing,” says Allison Henry, a marine biologist at the National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center in Woods Hole, Massachusetts, who was not involved in the work.

In the mudflats, the prey are 10 times more concentrated than in deeper water, Calambokidis reported, letting the whales consume up to 300 metric tons of shrimp while feeding in the delta. “These whales are really important ecologically,” says co-author David Cade, a marine biologist at Stanford University’s Hopkins Marine Station in Pacific Grove, California. That’s because they turn over a lot of sediment and cycle the shrimp back into the food web.

The whales first appeared more than 25 years ago when there seemed to be a food shortage, and more showed up in 1999, during similar conditions, Calambokidis explained. Hunger may have driven Earhart to try something new, and she gradually showed others the way to this jackpot, revealing unexpected social connections in the process.