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!

For bears, getting fat is a matter of life and death.

It’s been about six months since the brown bears of Alaska’s Katmai National Park — the bears of bear cam fame — emerged from their well-dug winter dens.

They’ve been munching on copious amounts of 4,500-calorie salmon ever since, putting on hundreds of pounds while thousands of people watched the bears' fishing antics on the explore.org webcams over the summer.

To recognize the animals’ keen survivalist ability amid a harsh bear world, Katmai is kicking off its annual Fat Bear Week competition starting Monday.

The bears go head-to-head in a playoff bracket, while the public (that means you) votes on who has gotten the fattest on Facebook.

The 2018 Fat Bear Week bracket Image: Bob Al-Greene/Mashable

“While it may be entertaining for us to watch, for the bears it's a game of survival,” Andrew Lavalle, a Katmai ranger who has closely observed the bears throughout the summer, said over email.

“They have to have enough fat stored up to last through up to six months of hibernation,” said Lavalle.

“Over the winter, they could lose one-third of their total body mass. In short, the more fat you have, the more likely it is that you'll come out of the den next spring.”

Fat bear matches happen every day between Wednesday, Oct. 3 through Tuesday, Oct. 9, also known as “Fat Bear Tuesday.”

Some of Katmai’s legendary heavyweights await the victors of Round 1.

The likes of the elder Bear 480 (a three-time winner), Bear 856 (the most dominant bear of the river), and 747 (a truly colossal creature) provide stiff competition.

Katmai National Park and Preserve Image: google

That said, the competition isn't simply a measurement of who’s the biggest and baddest now. It’s all about who got fattest over the course of the season.

How to Vote

Mashable will be posting daily updates announcing both the victors of the previous day's matches and the bears that are going head-to-head that day. Voting however, — which will be linked on our updates — is done through the Katmai National Park Facebook page.

Beginning each day at 10 a.m. ET, voting will begin as the park shows "dueling" comparisons of each bear in the early summer versus their enlarged October state. “Liking” the picture of a bear is how you vote. The day's winner is announced twelve hours after voting begins, at 10 p.m. ET.

On Tuesday, keep an eye out for Mashable's fat bear bracket voting guide. We'll introduce the individual bear competitors before first round voting begins on Wednesday at 10 a.m. ET.

And as always, remember to vote wisely, and vote often.