Scientists have confirmed what native Alaskans have observed for centuries - winds influence the travel patterns of northern fur seal pups. New research shows that strong winds can displace seal pups by hundreds of kilometres during their first winter migration.

Native American fishermen in Alaska have known that seal pups go with the wind rather than struggle against it. A new research study confirms that. Migrating northern fur seal pups travel hundreds of kilometres farther in blustery years than in calmer years. (Credit: Eric Boerner, Alaska Fisheries Science Center, NOAA Fisheries Service)
Native American fishermen in Alaska have known that seal pups go with the wind rather than struggle against it. A new research study confirms that. Migrating northern fur seal pups travel hundreds of kilometres farther in blustery years than in calmer years. (Credit: Eric Boerner, Alaska Fisheries Science Center, NOAA Fisheries Service)

Most northern fur seals breed on islands in the Bering Sea during the summer and embark on an eight-month-long journey to the North Pacific Ocean to forage for food in November and December of each year. For unexplained reasons, seal births have been declining there since the late 1970s, prompting increased research into the animals' behaviour. Researchers found many pups die during their initial migration from the Bering Sea to the North Pacific Ocean, but the rate at which this happens varies from year to year and scientists were unsure why.

Now new research compared the movements of individual seal pups during their migration with reconstructions of ocean surface winds. The results showed that as wind speed increased, seal pups moved downwind and to the right, most likely following wind-driven ocean currents.  The scientists found that surface winds could displace individual seal pups by hundreds of kilometres during their first winter migration. It is unclear whether being blown downwind is helpful or harmful to the seal pups, but the results offer a new insight into environmental effects on seal survival, according to the researchers. "They're at the whims of what's happening in the environment of the North Pacific Ocean," said Noel Pelland, a physical oceanographer and lead author of the study.

Northern fur seals are among the most long-studied marine mammals because of their historical importance to the fur trade. They have been hunted by native Alaskans for thousands of years and have been commercially harvested for their fur since Europeans arrived in Alaska in the 18th and 19th centuries.

A male Northern fur seal (Callorhinus ursinus) basks on the rocks with his harem in the Alaska Maritime National Wildlife Refuge. Northern fur seals have been a staple food of native Alaskans for thousands of years and have been commercially hunted for their fur since the 18th and 19th century. (Credit: M. Boylan [Public domain], Wikimedia Commons)
A male Northern fur seal (Callorhinus ursinus) basks on the rocks with his harem in the Alaska Maritime National Wildlife Refuge. Northern fur seals have been a staple food of native Alaskans for thousands of years and have been commercially hunted for their fur since the 18th and 19th century. (Credit: M. Boylan [Public domain], Wikimedia Commons)

For their research Pelland and his colleagues analysed data from more than 150 seal pups equipped with tags that allow satellites to track their movements. The researchers compared the pups' movements to models of wind speed and intensity in the North Pacific from 1997 to 2015. They found that during years when strong winds blew from the west, the pups ended up farther east, in the Gulf of Alaska. But in years when winds were weaker and came from the north, the pups ended up farther south, closer to the Aleutian Islands. It is not clear which scenario is better for seal pup survival. However, Pelland said, the results confirm anecdotal evidence of seal migration behaviour observed by native inhabitants of the Aleutian Islands that seals always travel with a fair wind and dislike traveling against the wind. "What's cool is that with this project, we have this sophisticated technology that allows us this unprecedented look at the lives of individual animals, and what it allows us to do is quantify things that may have been known for millennia," Pelland said.

Populations of northern fur seals are considered “depleted” under the Marine Mammal Protection Act. Unfortunately, they have not rebounded in recent decades despite a hunting ban. Lengthier, more physically challenging journeys in some years may explain this. (Picture: U.S. Fish and Wildlife Service [Public domain], via Wikimedia Commons)
Populations of northern fur seals are considered “depleted” under the Marine Mammal Protection Act. Unfortunately, they have not rebounded in recent decades despite a hunting ban. Lengthier, more physically challenging journeys in some years may explain this. (Picture: U.S. Fish and Wildlife Service [Public domain], via Wikimedia Commons)

Source: American Geophysical Union / ScienceDaily / NOAA