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Welcome to Fat Bear Week at Mashable! Each fall,Watch Secret Sessions Online 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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The Fat Bear Week finals showdown is nearly set: Profoundly plump Bear 409 (also known as Beadnose) awaits the winner of Monday's semifinal showdown.

The match pits two of the largest and most dominant Brooks River bears against one another: Bear 32 "Chunk" and Bear 747.

Voting opened at 10 a.m. ET on the Katmai Facebook page and the winner will be announced at 10 p.m. ET. You can vote simply by clicking on the image of bear you wish to vote for, and then "Liking" that image.

To help you make an informed vote, view the bears' dramatic summer to fall transitions below:

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Left:Skinny Bear 32 Original image has been replaced. Credit: Mashable Right:Fat Bear 32 Original image has been replaced. Credit: Mashable Left:Skinny 747 Original image has been replaced. Credit: Mashable Right:Fat 747 Original image has been replaced. Credit: Mashable

Each bear that regularly visits the Brooks River in Katmai National Park is given a number by park biologists. The massive Bear 747 just happened to "grow into" his given number.

Both bears are large enough to demand the best fishing spots along Alaska's Brooks River, where thousands of daily viewers watched bears snatch fish from the frigid stream on the explore.org webcams this summer.

SEE ALSO: Bear hibernation is a superpower, but it comes with a cost

Last year, Bear 32, nicknamed "Chunk" years ago by park rangers, proved to be the most dominant bear of the river, capitalizing upon an enfeebled Bear 856 (who had previously commanded the river's bear hierarchy since 2011).

Original image has been replaced. Credit: Mashable

But this year, a rejuvenated Bear 856 returned to form and has stood unopposed for the best fishing spots -- even from the likes of Bear 747 and Chunk.

Unlike Bear 856, however, Bear 747 focused most of his attention this summer on eating copious amounts of salmon. Some dominant males -- like Bear 856 -- will sacrifice valuable fishing time to seek and mate with females.

This might be a good strategy for passing along one's genes and propagating offspring, but it puts a bear like 856 -- who was taken out earlier in the week by Chunk -- at a clear disadvantage in the Fat Bear Week contest.

Bear 747's girth serves as ample evidence.

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