Welcome to Fat Bear Week 2019! Katmai National Park's bears spent the summer gorging on 4,500-calorie salmon, and they've transformed into rotund giants, some over 1,000 pounds. The park is holding its annual playoff-like competition for the fattest of the fat bears (you can vote onlinebetween Oct. 2 and Oct. 8), and Mashable will be following the ursine activity. 

After achieving viral fame on the internet last year, Bear 409 triumphed as the 2018 Fat Bear Week victor.

But this year, Bear 409, aka "Beadnose," isn't in Katmai National Park's Fat Bear Week bracket. In fact, the well-known champion and veteran explore.org bear cam bear hasn't been spotted this year, at all.

"When we last saw her, she appeared very fat and just as healthy as any other bear," said Mike Fitz, a former park ranger at Katmai National Park and currently a resident naturalist for explore.org.

"Yet, she wasn't seen at the river this summer and her absence remains unexplained."

And it may remain unexplained.

Although the fat bears spend their summer under the eye of the bear cams, often have nicknames, and have achieved global recognition, they are wild animals in a particularly wild realm. They aren't ever safe from the whims of the wilderness, the callousness of winter, or failing health. But by fattening up before the long winter famine, bears can give themselves a good shot at surviving another year.

"Bears rely on body fat for fuel and hydration during hibernation, so Beadnose appeared well-positioned to survive hibernation last winter," explained Fitz. "However, body fat isn't the only factor that affects a bear's overwinter survival. Like any large, long-lived mammal, they suffer from a variety of ailments."

Bear 409 is now over 20 years old, which means an aging bear. A brown bear's average life span is around 20 years. She's lived a rich life, having raised four litters of cubs.

Both younger and older bears that have been frequently observed by rangers at Katmai National Park's Brooks River (where the bear cams are situated) do fall off the radar. Some return, some never do.

One of the oldest known bear cam bears, Bear 410, vanished from the river last year. Rangers haven't spotted the roughly 30-year-old, legendary bear since. Her fate is a mystery. Though, 410 has well-surpassed a brown bear's life expectancy.

If 409 doesn't appear at the Brooks River next year, her disappearance will remain a mystery, too. Such are the rules in the remote Alaskan wilderness, where the wild world beyond the bear cams unfolds without the influence, eyes, or ears of humans.

Or, perhaps, Beadnose simply found richer fishing grounds this year away from the cameras. Katmai's bears do have their choice of salmon-clogged creeks, rivers, and streams.

"The possibility remains that she's making a living somewhere else in Katmai," mused Fitz.

But this seems less likely with Beadnose as she's been seen at Katmai National Park's Brooks River every year for the last two decades.

Except this year.