Welcome to Fat Bear Week 2021!Katmai National Park and lucah streamPreserve’s brown bears spent the summer gorging on 4,500-calorie salmon, and they've transformed into rotund giants, some over 1,000 pounds. The Alaskan park is holding its annual playoff-like competition for the fattest of the fat bears (you canvote onlinebetween Sept. 29 through Oct. 5). Mashable will be following all the ursine activity.

Among the fat bear titans stands a fearless bear mama.

The fat bears of Katmai National Park and Preserve live in a world defined by an intense hierarchy. And in this pecking order the biggest bears, typically males, earn access to the best fishing spots.

But some female bears, particularly bear 128 (aka "Grazer") have bucked the hierarchy. This summer, Grazer, an aggressive bear, established her presence among the big boys in Katmai's salmon-filled Brooks River. When bears would move into her territory, she would often hold her ground, and sometimes attack.

"Grazer has been a force this year," said Mike Fitz, a former Katmai park ranger and currently a resident naturalist for explore.org, the foundation that runs the livestreamed bear cams. "There's an argument to be made that she is as dominant as the biggest adult males at the river."

Grazer has been especially forceful the last two summers. In the first clip below, she charges at two bears, quickly scaring one off. The remaining bear, which Grazer proceeds to aggressively approach, is the largest and perhaps most consistently dominant of the fat bears: That's bear 747, voted as the 2020 Fat Bear Week champion.

Grazer displayed dominance last year, too. The second clip, from 2020, shows Grazer atop the Brooks River waterfall with her two cubs. She charges a large bear, perhaps because she felt it threatened her family or fishing opportunities.

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At times this summer, Grazer wasn't simply aggressive; she was outright violent (at least from the human perspective). In July, a younger bear tried to steal a fish from Grazer and her nearby cubs. Grazer, perhaps recognizing that she needs bounties of fish for both herself and her offspring, grabbed the other bear in her jaws. She mauled the hapless bear.

"Grazer will feel very defensive when she feels her cubs are threatened," explained Naomi Boak, the media ranger at Katmai National Park and Preserve. Boak observed Grazer's behavior from a bear-viewing platform in Katmai this summer.

Unlike some dominant males, who at times put on assertive displays for the sole purpose of showing how dominant they are (like pushing another bear out of the river), Grazer is "situationally dominant," explained Boak. This means she displays robust bursts of power and aggressiveness when she must (like telling another bear to back off from her cubs). It works. These extremely powerful displays intimidate other bears.

"This makes her one of the most dominant bears on the river," said Boak.

Yet Grazer isn't the only dominant female of Katmai's fat bears. Another veteran mama bear, bear 854 "Divot," is also a tough, intimidating force on the river. Divot, once a victim of a hunter's wire trap that snapped around her neck, fishes near the Brooks waterfall with other dominant bears. Boak has observed Divot commanding space for herself and her cub, at times intimidating some of the largest males.

"She is one fierce mama," noted Boak.

These mothers have profoundly challenging jobs. First-year cubs are often largely helpless; mom must catch enough food for herself and two or three other bears. She must ensure her cubs aren't threatened by any aggressive male bears, and watch for a slue of environmental risks, like fast-moving water.

And to boost the odds of her cubs' survival by scoring the most fish, she might choose to directly compete with Katmai's largest, most imposing male bears.

"All hail the females of the Brooks River," said Boak.