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!

Over the course of just three hours in late June, ecologist Mike Fitz stood atop a bear viewing platform in Alaska's Katmai National Park and watched Bear 747, a dominant male, consume 15 whole salmon.

"That's about 67,000 calories," Fitz, a former Katmai ranger, said over email.

Fitz has now endorsed Bear 747 as Fat Bear Week's fattest bear and believes the titanic animal — whose belly is nearly dragging on the ground — is likely to prove victorious in the Fat Bear Week bracket over such formidable contenders as Bear 480, a three-time champion.

We're entering the last few weeks of weight gain before Fat Bear Week commences. Here's a look at 747 (foreground) and 480 (background). Which bear seems to have gained the most weight so far this season? pic.twitter.com/OPNvS6VvB6 — Katmai National Park (@KatmaiNPS) September 8, 2018

Even nearly a month ago, 747 looked incredibly hefty.

It's normal for bears to exhibit hyperphagia, or excessive hunger, during the summer months.

This is almost certainly an advantageous adaption as brown bears must live off their stored body fat during the long winter famine.

But 747 has taken it to the extreme.

According to Fitz, who spent the summer in Katmai documenting bear activity, 747 arrived at the salmon-rich Brooks River on June 25, "and he never left for very long."

Bear 747 Image: Bob Al-greene/Mashable

Most years, bears leave the Brooks River in August when the salmon run declines. But this year was starkly different. Many bears stayed to capitalize upon a consistently rich run of salmon — 747 included.

"Bear 747 is an adult male in the prime of his life," noted Fitz on his blog. "First identified as a subadult bear in 2004, he’s matured into the largest bear I’ve ever seen."

"The belly clearance with the ground is the thing that really stands out to me about 747," said Andrew Lavalle, a park ranger at Katmai. "It almost drags."

"He seems to be more hippopotamus than bear at times," added Lavalle.

Bear 747 — who was given that bear ID number by park biologists long before "growing" into it — has found success by expelling little energy while fishing.

The 2018 Fat Bear bracket. Image: bob al-Greene/mashable

"He, like many of our more dominant bears, has learned that patience is key and to simply let the fish come to you," said Lavelle. "Do not expend calories trying to chase after them."

These fat bears, while an entertaining natural phenomenon, are illustrating their impressive survivalist abilities. And, it should be noted, they're able to accomplish this in a protected wild land — a national park nearly untrammeled by development.

The forthcoming Fat Bear Week champion, however, is still far from decided. Watch for Mashable's daily face-off announcements and results as the contest unfolds.

Details about voting, which begins Wednesday, Oct. 3 on Katmai's Facebook page, can be found here.