Day 1 of Fat Bear Week pits a former champion against a young upstart

Welcome to Fat Bear Week at Mashable! Each fall, Katmai National Park holds a competition as Alaska’s brown bears finish fattening up for their long winter hibernation. This year, Mashable is getting in on the salmon-munching action. Check back with us all week as we follow the fat bear face-offs each day, and remember to get your votes in for each round. Happy fishing!

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Update Oct. 3, 2018 at 11 p.m. ET:Former champion Bear 409 "Beadnose" easily advanced past Bear 151 "Walker." Meanwhile, Bear 854 "Divot" outpaced the young, but growing, Bear 503.

Both winners advanced to the quarterfinals and will meet their next formidable opponents on Oct. 5.

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It borders on nearly inconceivable that any wild animal can grow so exceptionally plump over the course of just four months. But, it's happening.

The voting for Fat Bear Week in Katmai National Park -- where bears are blessed with a copious supply of sockeye salmon that allows them to fatten up tremendously before hibernating -- has opened up, and there are two matches in play on Wednesday.

Match 1 pits former Fat Bear Week champion Bear 409, known as "Beadnose," against the still-growing adult male Bear 151, called "Walker."

The second match of the day, posted at 4 p.m. ET, pits Bear 845, or "Divot," against Bear 503.

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Both these bears also have rich histories. Four years ago, divot survived a severe wire-trap that sliced an inch into her neck, while Bear 503 was adopted by Bear 435 ("Holly") after being abandoned by his biological mother.

Bear 409 Credit: bob al-greene/Mashable Bear 151 Credit: BOB AL-GREENE/MASHABLE

Voting is done through the Katmai National Park Facebook page, where the park presents images of each skinny bear in June, versus their enlarged fall appearance.

Bear 854 Credit: bob al-greene/Mashable Bear 503 Credit: Bob Al-greene/Mashable

Voting is easy.

To vote for your choice, click into the photos of each large brown bear. Click the "Like" button for whichever bear you think has grown the fattest over the course of the season.

The park will announce the winners at 10 p.m. ET each day.

Left:Skinny Beadnose Beadnose fishing. Credit: NPS Right:Fat Beadnose Beadnose sitting. Credit: NPS

Fat Bear Week is certainly entertaining for us far-off viewers. But for the wild animals, growing fat is essential.

Left:Skinny Walker Bear 151, Walker. Credit: NPS Right:Fat Walker Bear 151, Walker. Credit: NPs

The bears lower their metabolism to extreme degrees during winter hibernation.

Yet, the energy they do consume is believed to come almost entirely from their fat stores. Fatter, in short, isn't just better for bears -- it's a big-time adaptive advantage.

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