Sound Recordist Dave Ruddick goes through his set-up and explains how he records surround sound in Tongass National Forest. A behind-the-scenes look at what goes into the making of a nature documentary.

After the tides have proven a challenge during a shoot on Admiralty Island, the Fortress of the Bears film crew has to get creative in order to keep their boat from getting stranded. A look at the challenges that can pop up when filming nature documentaries.

Filmmaker Shane Moore and Assistant Cameraman Michael Mauntler recap on the time they spent on Alaska’s Admiralty Island and discuss the challenges and dangers that come with filming bears in their natural environment. A behind-the-scenes look at what goes into the making of a nature documentary.

Fortress of the Bears filmmaker Shane Moore reveals some of the filming techniques he used during his shoot on Alaska’s Admiralty Island. A behind-the-scenes look at what goes into the making of a nature documentary.

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. Beginning in August, millions of salmon — pink and chum, coho and sockeye — return to the island to spawn, providing a feast for the bears, eagles, orcas, sea lions and even the trees. As long as the salmon continue to arrive, all is well. 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.Buy the DVD. This film premiered on January 25, 2012. (Video limited to U.S. & Territories.)

Admiralty Island hosts the largest concentration of brown bears in the world. Watch video.

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

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

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.” 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. Fortress of the Bears premieres Wednesday, January 25 at 8/7 c.