Our favourite annual event, Fat Bear Week, just kicked off

...  right after an attack killed one contestant.

Let the chunk-off begin.

Voting started today in the annual Fat Bear Week contest at Alaska’s Katmai National Park and Preserve, with viewers picking their favourite among a dozen brown bears fattened up to survive the winter.

The contest, which is in its 10th year, celebrates the resilience of the 2,200 brown bears that live in the preserve on the Alaska Peninsula, which extends from the state’s southwest corner toward the Aleutian Islands. The animals gorge on the abundant sockeye salmon that return to the Brooks River, sometimes chomping the fish in midair as they try to hurdle a small waterfall and make their way upstream to spawn.

All of this can be watched online via live cam. Trust us, you can lose hours.

A bear's death delayed the contest

Organisers introduced this year's contestants on Tuesday — a day late — because one anticipated participant, a female known as Bear 402, was killed by a male bear during a fight on Monday.

Cameras set up in the park to livestream footage of the bears all summer captured the killing, as they also captured a male bear killing a cub that slipped over the waterfall in late July.

"National parks like Katmai protect not only the wonders of nature, but also the harsh realities," park spokesperson Matt Johnson said in a statement.

"Each bear seen on the webcams is competing with others to survive."

The nonprofit explore.org, which streams the uncensored bear cameras and helps organise Fat Bear Week, on Monday hosted a live conversation about the death. Katmai National Park ranger Sarah Bruce said it wasn’t known why the bears started fighting.

"We love to celebrate the success of bears with full stomachs and ample body fat, but the ferocity of bears is real," said Mike Fitz, explore.org’s resident naturalist.

"The risks that they face are real. Their lives can be hard, and their deaths can be painful."

Packing on the kilos for survival

The bracket this year features 12 bears, with eight facing off against each other in the first round and four receiving byes to the second round. They've been packing on the kilos all summer.

Adult male brown bears typically weigh about 270 to 410 kilograms in mid-summer. By the time they are ready to hibernate after feasting on migrating and spawning salmon — each eats as many as 30 fish per day — large males can weigh well over 454 kilograms. Females are about one-third smaller.

When fans vote in each round, they shouldn’t only consider the bear with the biggest belly. Bear fans are instructed to vote on the ursine that they believe "best exemplifies fatness and success in brown bears."

A taste for seagulls and a bear named after a jumbo jet

Bear 909 Jr., who last week won the Fat Bear Junior competition for the second time, will face Bear 519, a young female, in the first round. The winner will face the defending champion, Grazer, described as one of the most formidable bears on the river.

Another first-round match pits Bear 903, an 8-year-old male who was given the nickname Gully after he developed a taste for seagulls, against Bear 909, the mother of Bear 909 Jr. The winner faces a two-time champion, a bear so large he was given the number of the equally massive airplane, Bear 747.

One of the biggest bears ate 42 salmon

In the other half of the bracket, the first-round match has Bear 856, an older male and one of the most recognisable bears on the river because of his large body, challenging a newcomer, Bear 504, a mother bear raising her second known litter. The winner will face perhaps the largest bear on the river, 32 Chunk, a 20-year-old male who once devoured 42 salmon in 10 hours. He's estimated to weigh more than 544 kilos.

The last first-round match has Bear 151, a once-playful young bear nicknamed Walker now showing more dominance, versus Bear 901, a solo female who has returned to the river after her first litter did not survive. The winner will face Bear 164, called Bucky Dent because of an indentation in his forehead.

Voting in this year's tournament-style bracket is open until October 8.

More than 1.3 million votes were cast last year.

- With AP

Originally published as Our favourite annual event, Fat Bear Week, just kicked off