Strong winds send migrating seal pups on lengthier trips

PORTLAND, Ore. — Native American fishermen in Alaska have long said that seal pups go with the wind rather than struggle against it. Now, a new study confirms that wisdom. Migrating northern fur seal pups travel hundreds of kilometers farther in blustery years than in milder years, researchers reported February 14 at the American Geophysical Union’s Ocean Sciences meeting. Those epic journeys may be linked to pup deaths.

At 4 months old, the pups are weaned and begin a voyage from the Pribilof Islands of Alaska through the Bering Sea and North Pacific Ocean that can last for 20 months before they return to the islands. Physical oceanographer Noel Pelland and colleagues compared the migrations of 168 seal pups tagged in five different years from 1996 to 2015 with winds matching the pups’ first migration years. Winds were simulated using data from the U.S. National Centers for Environmental Prediction.

On average, the pups moved farther downwind when wind speeds were higher, and tended to move to the right of the wind direction — likely following wind-driven ocean currents. Tagging data lasted 130 days on average, but whether the pups died or the tags fell off is unknown. That makes it difficult to draw a definitive link to mortality, says Pelland of the National Oceanographic and Atmospheric Administration’s Alaska Fisheries Science Center in Seattle.

Still, the lengthier, more physically challenging journeys in some years may explain why populations of these northern fur seals — considered “depleted” under the Marine Mammal Protection Act — have not rebounded in recent decades despite a hunting ban.

Next the team plans to simulate seal pup migrations and compare those modeled journeys with decades of wind records. Hunting records from the mid-20th century include data on seal mortality, Pelland says; comparing these data might help identify a direct link between winds and pup deaths.