How fat are the bears of fat bear week?

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Welcome to the bear buffet at Brooks River in Katmai National Park, where brown bears bulk up on salmon for the long Alaskan winter and livecams stream their progress to viewers all around the world. In October, when the bears are at their fattest, hundreds of thousands of people vote in’s Fat Bear Week tournament to crown a champion.

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Bear #747

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The biggest of those bears, identification number 747, is one of the largest bears in the world. His weight has been estimated at 1,400 pounds. In fall, he gets so big that his belly hangs inches from the ground.

He started this season with a ripped ear and a hangdog expression. But after a summer of gorging on salmon, he has ballooned back to magnificent proportions. He is roughly the size of a side-by-side refrigerator, and would fill nearly a full row of airplane seats.

No. 747 has been a fat bear champion in the past, but he is just one of the many bears at Brooks River who has eaten their way to their biggest, best selves.


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These bears are not just getting fluffy. They are getting fat. Katmai bears can gain an additional 50 percent of body weight between midsummer and autumn. By October, large male bears can weigh over 1,000 pounds.

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“The big male bears are just balloons at this time of year,” said Mike Fitz, resident naturalist at and former National Park ranger.

Bear #32 “Chunk”

It is hard to imagine the sheer scale of these bears. Chunk, a big male with a scar across his muzzle, is estimated to weigh more than 1,200 pounds – roughly seven times the average American adult.

Chunk still scavenges leftovers from other bears’ salmon, despite measuring more than 6 and a half feet from nose to rump.

Smaller bears, like females and young adults, cannot pack on the pounds like Chunk because dominant male bears push them out of the best fishing spots. But young bears can elbow their way into the hierarchy as they grow. No. 151 Walker lost his fishing spots often as a playful young adult. Now, as an assertive 1,000-pound adult, he throws his weight around for the best positions on the river and is far less tolerant of other bears.

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Bear #151 “Walker”

It is a good thing Walker does not like company: He takes up nearly an entire king-size mattress by himself.

The bears don’t start the year this big. When they come to Brooks River in midsummer, they have run down their fat reserves from the previous year. Then sockeye salmon, fat from the ocean, begin their return migration up Brooks River, and the feasting season begins.

At this time of year, a dominant bear in a quality fishing spot can catch up to 30 sockeye salmon in a day. That’s roughly 150 pounds of fish – enough to make 600 sushi rolls.

For bear cams viewers, a big bear belly is a source of delight. But for the bears, it’s a matter of life and death. The food they eat across four months of summer and early autumn has to carry them through their winter hibernation and the lean months of spring, before salmon return.

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The bears bulk up not just to survive, but to reproduce. Mother bears must store enough fat to carry pregnancies to term during hibernation and then nurse their cubs until summer. Male bears need energy for the mating season, which gets underway before the salmon return.


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Many salmon populations are “hanging on by a thread,” notes Fitz. For the Katmai bears, they are lucky as the Brooks River sockeye population had three straight years of record breaking runs.

“Fat Bear Week is a celebration of success for these bears, and an opportunity to consider what they need in their environment,” said Fitz. “If we want bears in Katmai to remain healthy, we have to protect the salmon.”

— Bear weight, volume and dimension estimates provided by Joel Cusick of the National Park Service. Photographs courtesy of the National Park Service.

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