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NATURE: Fortress Of The Bears

Airs Wednesday, June 11, 2014 at 8 p.m. & Sunday, June 15 at 4 p.m. on KPBS TV

Brown bears on Alaska's Admiralty Island, which supports the largest concentr...

Credit: Courtesy of MacKenzie Moore

Above: Brown bears on Alaska's Admiralty Island, which supports the largest concentration of bears anywhere in the world.

Part of the massive Tongass National Forest, Alaska’s Admiralty Island is home to an estimated 1800 brown bears, the largest concentration of bears in the world. Nearly 100 miles long and 20 miles wide, it is half the size of Yellowstone National Park, yet it sustains four times more grizzlies. The native Tlingít people call this island “Kootznoowoo,” meaning “Fortress of the Bears.”

Brown Bear Fact Sheet

Is it a brown bear or a grizzly? The answer is that all grizzlies are brown bears, but not all brown bears are grizzlies. Read the fact sheet to learn more about brown bears.

It is a place where bears depend on fish, fish depend on trees, and the trees depend on fish-eating bears to spread the nitrogen rich bodies of salmon throughout the forest. Everything depends on the annual salmon run. When a change in the weather keeps the salmon from arriving, the entire ecosystem is affected.

A La Niña winter has cooled the water to two degrees below normal, keeping the salmon out of the streams and delaying the run. It’s the worst salmon season in the last 40 years.

As the bears wait for the salmon, they hunt and scavenge for anything they can find to supplement their unsatisfying diet of grass. The receding tide offers unique opportunities, and one young bear demonstrates a remarkable talent for clamming. But the feast is short-lived.

With the passing season showing no sign of fish, the bears become increasingly gaunt and desperate. Will the salmon finally make their way up the streams of Admiralty Island? And will the bears survive until they do? "Fortress Of The Bears" enters a world shaped by bears, trees, and salmon, and explores the delicate balance of their interconnected lives.

NATURE is on Facebook, Tumblr and you can follow @PBSNature on Twitter. Past episodes of NATURE are available for online viewing.

NATURE: Inside the Fortress

Part of the massive Tongass National Forest, Admiralty Island in southeast Alaska supports the largest concentration of bears anywhere in the world. Sustained by a wealth of salmon streams, isolated and protected by their environment, some 1,700 Alaskan brown bears are part of a unique circle of life that has played out here for centuries. But this year, the salmon fail to arrive for the first time, and the bears get a bitter taste of what the future may hold.

Fortress Of The Bears: A Desperate Mother

After a spring and summer with no sign of salmon, a mother bear is desperate to catch fish to feed her famished cub.

Fortress Of The Bears: A Heroic Return

It’s taken all spring and summer, but salmon finally return to Admiralty Island to spawn.

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