Everything You Want to Know About Katmai National Park’s Fat Bears

Every fall, Katmai National Park and Preserve in Alaska hosts Fat Bear Week, an annual tournament celebrating the success of the bears at the park’s Brooks River. From October 4 - 10, 2023, your vote will decide who is the fattest of the fat!

What is Fat Bear Week?

Fat Bear Week is a single elimination tournament in which Katmai National Park and Preserve invites its online community to compare photos of bears from when they first visit Brooks Falls in the spring to photos of the same bears at the end of summer. The differences are often huge. In just a few months, the bears have gorged on enough salmon to pack on some serious pounds. Fat Bear Week is fun, but it also brings up really important questions about survival and how we’re studying and learning more about these amazing bears.


Photo by National Park Service.

How can I participate in Fat Bear Week?

Celebrate the success of Brooks River’s world-famous bears during Fat Bear Week by placing your vote. Matchups will be open for voting between 12-9 p.m. ET (9 a.m.-6 p.m. PT) from Wednesday, October 4 to Tuesday, October 10, 2023.

By the end of the week, only one well-fed ursine will receive the title of the fattest bear. For each pairing of bears, you will be given the opportunity to vote on the bear of your choosing. Your vote decides which bear will be crowned the fattest of the year.

To make sure you’re making an informed choice, meet the bears, learn about previous champions or watch a livestream at the bears of Brooks River. You can base your vote on many factors, such as the bear’s growth, extenuating circumstances, or which bear you think is the largest. However, Fat Bear Week is a subjective competition, so be sure to vote and campaign for your favorite!

Big brown bear side by side comparison of skinny and fat bear
Bear 747’s weight gain between July and September is always impressive. Photo by N. Boak, National Park Service.


Holly, a perennial Fat Bear Week favorite, was the 2019 Fat Bear winner. Photo by K. Stenberg and L. Carter, National Park Service. 

How is bulking up beneficial to bear survival?

This week is about body positivity. A fat bear is a healthy bear! Fattening up as winter approaches is a matter of life and death for the bears: relying on stored fat for energy, they can lose up to a third of their body fat as they slow down for the winter. The more bulk they put on, the more likely they are to survive the long, cold months. And we think any fashion blog would agree that these bears look fabulous and are runway ready!

Fat brown bear
Bear 747 trudges through the water at Katmai National Park. Photo by N. Boak, National Park Service. 


Beadnose 409 was the 2018 Fat Bear winner. Photo by A. Ramos, National Park Service. 

How can they eat so much? What’s on the menu?

In the fall, they enter a physiological state known as hyperphagia in which they eat non-stop and can gain up to four pounds in a single day. Some bears can eat dozens of sockeye salmon each day, with each salmon packing about 4,000 calories.

A coastal brown bear’s diet during the summer consists primarily of salmon with the addition of sedge grasses and berries. The fat of the salmon is what allows for such tremendous weight gain in a limited window. Once bears enter hyperphagia in late summer, Leptin, the chemical that tells the body it’s full, is suppressed. This allows bears to eat until it’s time to sleep. One bear was spotted eating 40 salmon in a single sitting. During this time the bears practice a technique called high grading. This is where they select the most calorie-dense parts of the fish to eat, such as the brain, skin and roe, leaving the less fatty fillets behind.

How are you measuring the bears? 

Wild bears have always been challenging to measure. Terrestrial Lidar scanning technology is used almost exclusively in civil engineering fields to scan the interior of buildings, roads and gravel stockpiles to get volume measurements. As an experiment, it was used on bears at Katmai’s Brooks Camp! This was a challenge as the animals had to stay still and not move long enough to complete a scan. When the bears were standing at the top of the falls or in the river wafting to catch a fish, they were still enough that this technology worked well. This is an exciting, new, non-invasive way to collect information on the bear’s volume — especially because weighing bears is not an option. 

Fat bear in the water with salmon in its mouth.
Holly enjoys a meal in the water. Photo by N. Boak, National Park Service. 

Is there enough salmon? What’s the impact on available resources?

The last few documented salmon runs have shown high numbers — in 2019 it reached a record-breaking 62.3 million and 2021 broke that record again with almost 65 million sockeye. The 2022 salmon run was strong and healthy with aproximately 50 million sockeye. Right now, there are enough salmon to go around. The question is pointed toward the future. It’s difficult to know what kind of impacts the heat and weather patterns of this summer will have on future runs of salmon. The heat may have impacted egg survival and some streams may have dried before salmon had the opportunity to spawn. One summer may not tip the scales toward disarray, but if the heat and weather conditions continue into future years, it may be a different story. Scientists will continue to monitor and collect data regarding changes in the climate in order to help predict future trends and provide park managers with the information needed to care for this landscape.


Nice catch! A brown bear snags a salmon. Photo by M. Freels, National Park Service. 

Will female fat bears have cubs?

If a sow gains enough weight during the summer (and in this case it certainly seems she has) the chance of her having cubs is very high. After mating, the fertilized egg develops into a ball of cells known as a “blastocyst.” This blastocyst does not immediately attach itself to the uterine lining until the sow begins her torpor (semi-hibernation) state. This is known as “delayed implantation.” The sow must have enough fat reserves to continue the pregnancy, or the blastocyst may not implant itself. Cubs are usually born in the den in January or February with the actual gestation period only being about 3 months long.

Mother bear and her two cubs
A mama bear and her two cubs. Photo by M. Whalen, National Park Service.

What about the cubs?

At Katmai, cubs will generally stay with their mothers for two and a half years. During a cub’s first year of life, they are considered cubs-of-the-year or spring cubs. In their second year, they are generally called yearlings and will den with their mother for at least one more winter. Cubs generally stay close to their mothers, first nursing and then learning how to fish and hunt for themselves. Play among siblings is fun to watch but is also an important way for cubs to develop life skills. Male bears play no role in raising young and can actually be a threat to them.

Bears between two and a half and five years old are known as sub-adults. They are independent of their mothers, but not yet sexually mature. Some sub-adults have been part of Fat Bear Week, showing off a dramatic transition to chubby cubby.


Mama bear and cubs playing in the grass. Photo by James Beedle (www.sharetheexperience.org). 

Do bears really hibernate?

It is a common misconception that bears hibernate during the winter. While bears tend to slow down during the winter, they are not true hibernators. Black bears, Grizzly bears and Brown bears do go into a deep sleep during the winter months, known as torpor. At times, they will wake up and move around their dens.

Fat brown bear laying down.
A brown bear taking an after lunch snooze. Photo by D. Kopshever, National Park Service.

When do the bears slow down for winter?

The bears at Katmai National Park and Preserve will retreat to their dens to bed down for the winter in October or November. Bears south of Alaska usually enter their dens later and emerge sooner, but it all depends on winter conditions. They’ll stay there for until the late spring when they’ll emerge thin and hungry.


This brown bear is looking rather skinny and hungry upon emerging from its den. Photo by L. Pastweka, National Park Service.

How can I see the bears?

The easiest way to watch the bears is to tune in to the bear cams at Explore.org. From the comfort of your home or office, you can watch these fascinating animals as they go from thin to thick. People often pick favorites and cheer them on as they splash through the river and snatch leaping salmon from the air. The best times to watch the bears at Brooks Falls are from July to September, though some bears remain in the area through October. Katmai National Park and Preserve also updates their social media pages with excellent photos and wonderful information during the season.

If you really want to witness these impressive bears in person, it’s going to take some planning. Unlike most national parks in the United States, Katmai is almost exclusively accessed by plane or boat. For bear viewing, Brooks Camp is the most popular destination in the park where the National Park Service operates a visitor center, ranger station, campground and auditorium with daily ranger-led programs from June 1 to September 17. All visitors to Brooks Camp are required to begin their stay by attending a brief bear safety talk outlining the park’s rules and regulations. Trails lead visitors to viewing platforms, where bear fans can watch the feast unfold.

Bears in the water
Bears roam the waters and visitors look on. Photo by R. Taylor, National Park Service.

What was social media’s role in the rise of #FatBearWeek?

Social media played a pivotal role in the rise of #FatBearWeek. Katmai National Park and Preserve is remote, making it difficult for the average American to gain access. The role of social media in the Fat Bear Week campaign was to provide that access for those sitting at home. The use of the Explore.org live cams paired with comparison photos of the bears being featured encouraged virtual visitors to participate. Social media extended the invitation to the fat bear party.

Social media also provided a platform to share about the larger issues facing the park and ultimately the peninsula’s bears. At face value #FatBearWeek is a light, comical look at wildlife; but underneath that veil is a hearty dose of reality. Without access to clean water and healthy ecosystems unaffected by climate change or human influence, the fat bears we celebrated this year will be at risk. Just like the bears, we saw reports on from British Columbia, bears along the Alaskan Peninsula experienced the effects of warming water and struggling salmon. In the northern regions of Katmai National Park, commonly observed salmon streams dried up, sometimes with salmon still trying to swim upstream.


 You can watch many bears at Brooks Falls. Photo by Russ Taylor, National Park Service.

Bears are wonderful and interesting animals that command our attention and deserve our respect. Fat Bear Week is a celebration and a chance to learn more about our ursine friends. We hope you’re looking forward to the next Fat Bear Week as much as we are.