Grey seal's travels hint at animal's unknown habits

May 30, 2013 by Ashley Yeager
This juvenile male grey seal swam up onto a North Carolina beach recently, surprising locals. Credit: StarNews Online.

On May 23, visitors to Carolina Beach met an unexpected guest—a male grey seal.

The 300-plus-pound juvenile was somewhat of a surprise to North Carolinians, since his typical habitat ranges from the coastal waters of Canada and extend south to about New Jersey. It is the first time a has been seen as far south as the Carolinas.

But the seal's southern swim wasn't too surprising to Duke Dave Johnston.

"Things have been weird with for the last ten years or so. We've been seeing more harp, hooded and grey seals much farther south, usually the males," he says.

To track seals' travel patterns, Johnston and his colleagues have started attaching cell-phone enabled GPS tags to the animals in the region. They tagged their first grey seal, Bronx, last summer and from his transmissions alone have learned where the creatures like to hang out, how deep they can dive and just how far they can swim.

Bronx has covered the equivalent of the land area of Massachusetts and Connecticut combined during his swims. He's explored below the ocean depths nearly 900 feet—a little more than a tenth of a mile, and he's even made an international trip, crossing into Canadian waters.

But Bronx swims mostly in the waters near Cape Cod and Nantucket Islands, Johnston says.

This map shows where a GPS tagged seal, Bronx, has swum since last summer. Credit: Dave Johnston, Duke

Grey seals like Bronx have had a rough history in the region. In the 1800s, humans hunted and killed the entire population living in the . For a long time, there were few or no sightings of the animals. But since 1972, grey seals have been protected under the Marine Mammal Protection Act and are now returning in larger numbers to the shores of what was once their native habitat.

Some Cape Cod locals aren't too happy about that. The seals come ashore in large groups, disrupting beach access in certain areas, and they leave behind their waste. They get caught up with fishermen's gear and try to steal their catch, and the seals aren't the friendliest marine mammals.

"People like dolphins. They tend not to like seals as much," Johnston says, explaining that grey seals are smart, excellent predators and can be aggressive towards humans. "They can be loud and obnoxious, and they will bite," he says.

That's a challenge for both the seals and residents of the Cape Cod.

Part of the tagging effort is to increase people's understanding of how grey seals interact with the ocean environment surrounding Cape Cod, and it could possibly explain why some of the animals are swimming as far south as the Carolinas.

The team is heading to the Cape Cod in early June to attach tags to seven more grey seals. The goal is ultimately to use the tracking data to improve the relationship between humans and seals there, Johnston says.

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