They move like ghosts along the shorelines of Canada's Vancouver Island, so elusive that people rarely see them lurking in the mossy forests.

British filmmaker Bertie Gregory was one of the lucky ones: He saw coastal wolves—also known as sea wolves—in 2011.

"There is something about being in the presence of a coastal wolf—they just have this magic and aura around them," he says.

That experience inspired him to return and document the animals for National Geographic’s first YouTube series, wild_life with bertie gregory, which launches August 3.

“Coastal wolves are such a unique predator, and they are hunting in this absolutely epic landscape,” says Gregory. Roughly the size of Maryland, the island and its remote western fringes are still a wild frontier in the Pacific Northwest. (Read "In Search of the Elusive Sea Wolf Along Canada's Rugged Coast.")

Chris Darimont, science director at the Raincoast Conservation Foundation, has studied the carnivores' unusual lifestyle for nearly two decades. He shared some intriguing facts about this little-seen population of gray wolf.

There are two types of coastal wolves.

There are two populations: mainland coastal wolves and coastal island wolves, the latter being the focus of Gregory’s quest. “The mainland coastal wolves are every bit as 'coastal,' though they do eat less seafood compared to those on islands," Darimont says.

Their lives revolve around the ocean.

Unlike their inland cousins, coastal island wolves are entirely dedicated to the sea. Their genes prove it; collectively, coastal island wolves have distinct DNA that sets them apart from interior wolves, according to a 2014 study published in BMC Ecology.

Though such genetic differences within wolves is not uncommon, discovering it in an area as small as the west coast of Vancouver Island is, says co-author Erin Navid, a research grants officer at the University of Calgary.

"Wolves are highly mobile animals; they have home ranges that are hundreds of kilometers in area and they are capable of crossing many types of natural barriers, including small bodies of water," she says.

"When we think about genetic differentiation, we imagine animal species that are separated by large distances will be genetically different from one another."

Up to 90 percent of their diet is seafood.

People usually associate wolf meals with elk or deer, but these guys are practically pescatarians, with salmon accounting for nearly a quarter of their diet. Beyond that, they forage on barnacles, clams, herring eggs, seals, river otters, and whale carcasses. (See more photos of coastal wolves.)

They’re excellent swimmers.

Coastal wolves live with two paws in the ocean and two paws on land, Darimont says. When hunting for food, sea wolves can swim miles between islands and rocky outcrops to feast on seals and animal carcasses found on the rocks. “Our farthest record [of their swimming abilities] is to an archipelago 7.5 miles [12 kilometers] from the nearest landmass,” he says. (See 12 of our favorite wolf pictures.)

They're about the size of a German shepherd.

They’re smaller in stature than gray wolves in other parts of the country, another effect of their diet. “Interior wolves are about 20 percent bigger, maybe like a [Great] Pyrenees,” Darimont says. Additionally, they're often reddish brown in color.

Vancouver Island isn’t the only place they call home.

More populations reside in southeastern Alaska, though overall sea wolves have declined in number over time. “They once roamed all the way down to California in its former temperate rain forests. Now they only go down to just north of Vancouver," he says.

"This should remind us to take good care of them."