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fat bear scan blog

How Big are the Fat Bear Week Bears?

By Mike Fitz

Fat Bear Week is over for another year, and Holly has claimed the title of the fattest bear of 2019. She is a true champion of Katmai National Park, an individual who exemplifies skill and success in the bear world. In Katmai, fully grown and well fed adult female bears like Holly can often tip the scales at 600-700 pounds and Holly is probably well within, or even exceeds, that weight class. Based on her overall size though, how might she compare to other bears in Katmai? And just how big can a Katmai bear grow? Now, thanks to unusual use of terrestrial laser scanning technology, we have some answers.

435 Holly Fat Bear Week Champ

Holly is the reigning queen of fat bears. She was voted the fattest bear of 2019 in Katmai National Park’s annual Fat Bear Week tournament.

The size and weight of wild bears has always been problematic to measure. You can’t just walk up to a bear with a tape measure and tell it to hold still or expect it to stand on a scale. Hunter-killed bears can provide some info, but the “record” bears documented by the Boone and Crockett Club are ranked on skull size, not body mass. Biologists will sometimes weigh and measure wild bears as part of their studies, yet this requires tracking and tranquilizing animals. While the methods and procedures used to tranquilize bears are well tested and reliable, biologists cannot eliminate all risk to themselves or the animals. Therefore, the application of non-invasive technology may provide ways for people to satisfy their curiosity and learn more about wildlife without interacting or harming them.

Similar to echolocation used by bats, terrestrial laser scanning technology sends out a series of laser beams that “echo” off an object. The returning signal is recorded by the scanner. Specialized computer software is then used to render a three-dimensional computer model of the object or place. The process is frequently used by civil engineers, GIS specialists, and surveyors to document, analyze, and monitor roadways, gravel pits, mining sites, and buildings. The scanning technology also determines an object’s volume very precisely without the need for a person to physically measure it, which brings me back to bears.

In their effort to gain as much fat as they can before winter hibernation, dozens of bears have come to rely on Brook Falls as a place where they can wait for salmon to come to them. Experienced and skilled bears know patience is the key to success at the falls. By sitting or standing and waiting for salmon to come to them, they can make a huge profit in calories without expending much energy.

Because terrestrial laser scanners need to record thousands and sometimes millions of data points to achieve a reliably accurate rendering of a subject or landscape, the object of interest needs to remain stationary. Where might wild bears remain still long enough to complete an accurate scan? Brooks Falls.

On September 16, Joel Cusick, a geographic information specialist with the National Park Service’s Alaska Regional Office, set up a Trimble SX10 scanner on the elevated wildlife-viewing platform adjacent to Brooks Falls. He then waited for good opportunities to scan bears fishing there. Good opportunities came when a bear stood still and did not have a significant portion of its body submerged in the water. To get an accurate scan, a bear had to remain stationary for about 16 seconds.

Five bears stood still long enough—32 Chunk, 151 Walker, 480 Otis, 747, and 854 Divot. Two bears, Otis and Walker, were scanned more than once from different locations, which allowed Joel to combine the scan data for a more accurate model of the bear. Other bears were present as well but were too obscured by water or did not remain still long enough to get an accurate scan.

On the computer afterward, Joel processed the scans to exclude nearby objects like rocks. Since the scanner only saw the bear from one side, it only recorded half a bear’s volume. Once the images were cleaned of non-bear objects, the animals’ true volumes were calculated by doubling the original value. (Of course, this presumes that bears are completely symmetrical. They are some irregularities, but I don’t think Otis’ floppy ear or any other asymmetry would make a significant difference.)

480 scan slices

Spread over 1.5 hours, Otis occupied nearly the same position at the falls, which allowed his volume to be determined with high precision.

Although volume isn’t the same as mass, it’s somewhat easy to calculate an object’s mass when you know its volume and what it is made of since mass is a product of density and volume. In other words, just multiply an object’s density by its volume and you are left with its mass. With bears, the math is complicated slightly by the fact that bears aren’t made of only one type of tissue. Like our own bodies, they are a combination of water, muscle, bone, organs, and especially at this time of the year, fat. Because the bears at Brooks Falls were not physically handled, only estimates of their body composition were used to calculate their mass.

Brown bears in this area are often around 35% body fat in late summer and fall. For simplicity, the rest of the bear was considered to be the lean tissue, which is about the density of water. With the math complete, we now have a good idea of what the bears weighed on the day of the scans. The 2019 Fat Bear Week tournament was full of truly fat bears.

Screen Shot 2019-10-11 at 10.48.02 AM


These statistics illustrate that Katmai’s bears are some of the biggest in the world. In the Greater Yellowstone Ecosystem, where bears have to work much harder to find nutritious food, adult females average 296 pounds and adult males average 457 pounds during September and October. Even 854 Divot, a mature female who is not particularly large compared to Katmai’s adult males, is almost 700 pounds. I’ve long thought 747 was a very big bear, frequently stating that he’s the largest I’ve ever seen and that he might weigh 1,200 pounds. Now, I know that was likely an underestimate! As Katmai National Park posted on their Facebook page, 747’s volume on September 16 was about the size of a side-by-side refrigerator. At over 1,400 pounds, he’s probably larger than 99% of all brown bears, and he might be within a couple hundred pounds of the biggest wild brown bear ever recorded.

747 Fat Bear Week comparison

The mighty 747 is one of the largest bears living on Earth today.

When I corresponded with Joel Cusick, he was careful to note that while the weights are impressive, it’s the volume measure that is more accurate since the bear’s body composition could only be estimated. The test project also lacked a control. To ensure its accuracy, it would need to be used on bears from a captive facility where researchers can physically measure and weigh the bears to compare the results with those of the laser scans. Even so, the scans from the falls provide us with a reasonable estimate of their weight, perhaps even within 50 pounds.

This is the first ever application of terrestrial laser scanning technology on wildlife. When we apply technology in an unconventional way, we might be able to better satisfy our curiosity. More importantly, we might be able to track the growth of bears at Brooks Falls without the risks associated with drugging and handling them. That information could be coupled with salmon escapement numbers or an individual bears’ fishing success to more fully understand the factors that influence their summertime growth. Like watching wildlife through a webcam, it could allow us to learn more about them without disturbing or altering an animal’s behavior. Perhaps one day, we’ll be able to do more than just guess how much bears like 747 or Holly weigh in June, July, and September. We’ll be able to follow their growth from skinny to fat with precision.

  • stadawg

    Very interesting!! Is width a part of that as well? Since 747 is definitely wider than most bears. Would love to see what 856’s weight was. Also found it strange that Walker was heavier than Otis since Otis is a much larger bear. I know Otis hadn’t gained as much weight early in the season as usual, but still, 250lb difference is quite a bit.

    Thanks for the great info!!

    • https://fitznaturalist.com Mike Fitz

      To accurately asses a bear’s volume, the scans needed to take width, height, and length into account.

      I too was a little surprised by 151 Walker’s size. However, the most reliable and best scan was of Walker, according to Joel Cusick. Walker has apparently grown quite a bit recently. A bear’s height and length isn’t necessarily indicative of it’s true volume either. Otis might appear taller than Walker, but he isn’t as well filled in. Walker was very fat this fall.

      • stadawg

        Agreed. I just thought it was very interesting! I was like, WOW, 250lbs?? Good for him. I know Otis has put on a LOT of weight as well lately. Didn’t even realize it, but Walker is even heavier than CHUNK!! LOL!

        Thanks for all your work!!

        • DeeBayArea

          I know. That is what is shocking. Walker is bigger than Chunk!

  • FionaBRZ

    Fascinating: and what a great new use of an existing non-invasive technique. I would love to know what Holly’s mass is this year! Also, is it a coincidence, do you think, that almost all the bears who stood still for long enough were large males? Are they perhaps less likely to be challenged for their spot when feeding than other bears?

    • https://fitznaturalist.com Mike Fitz

      I don’t think it is any coincidence that four out of the five bears who could be scanned accurately were large adult males and the fifth was a mature adult female. Bears of that size and age are typically more patient when fishing and, like you mention, less likely to be displaced from fishing spots than other bears. Divot, I should note, was scanned while she was sleeping on the beach near Brooks Lodge. It wasn’t an ideal position since her belly wasn’t visible, but it was good enough to get a volume estimate.

      • FionaBRZ

        Thank you for the reply, Mike. Are there plans to scan next year too?

        • https://fitznaturalist.com Mike Fitz

          I don’t know. I would welcome more scans of the bears. However, it might be more important if this application of the technology is fine-tuned in a more controlled setting first. That way, when it is used at the falls again, there might be less margin for error.

          • DeeBayArea

            If it would cost to do the scans, I am sure we could collect money. I know that I would give money to see more bear scans.

      • Karlab

        And they are the ones who are conserving the most energy by not moving around too much, right? Otis is a champ at this! He’s just standing there, and then he’s eating a fish.

        • https://fitznaturalist.com Mike Fitz

          Yes, each one of the bears scanned at the falls was demonstrating good energy economics. They were moving little and waiting for their meals to come to them.

  • KatmaiConservancyRangerNaomi

    Thanks for this great bog, Mike. It was thrilling to be part of this experiment. And, of course, thrilling to chart just how BIG 747 is.

  • Smokefancj

    For those of us who may never make it to Katmai, this is awesome information. I’ve got a whole new perspective on how big these boys, and lady, are! We always worry about Walker getting pushed aside but now know he’s literally one of the BIG boys :) And I also feel like I have a better idea of the male vs female sizes.

  • Smokefancj

    I wonder if Ranger Roy is following all of this?? Wish he was around so we could get his perspective too! :)

    • DeeBayArea

      I miss Ranger Roy. Mike and Roy were a good team.

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  • mosaic_world

    it is perhaps a good thing that Lefty and Holly did not have their scans done this year… lest there be a minor controversy about the results of the fat bear contest! (j/k) <3 <3 <3 … thank you for the article. very interesting study and results…

  • http://www.teatrremus.pl/ Kasia

    This is really, really cool stuff! Thank you so much :-) Mike – do you have pictures of the scans of Walker, Chunk, and Divot? Maybe we could have a little fun trying to ID which is which from the scans, if you cover the name and adjust the size, so that it’s not immediately obvious which is Divot?

  • Emil

    Fascinating. And 747 lives up to his number.

  • Jackie CJB

    Very, very interesting! Thanks so much!

  • Elizabeth Wilkins

    This is so very interesting! TY for providing this somewhat surprising infor on these bears.

  • cma319

    WOW. Amazing. Great blog post. I wonder what Otis weighs now. He seems to be continuing to eat so much, and we are seeing so much more of him than some of the other bears.

    • https://fitznaturalist.com Mike Fitz

      Otis is certainly fatter now than he was in mid September, especially since he’s continued to fish for salmon. In late summer and fall, when bears have access to a lot of food at Brooks River, they can gain 2-4 pounds per day.

  • MaryAnn Bova

    747 is as big as a 747!
    good GOD almighty that’s a whole lotta brown bear. https://media0.giphy.com/media/PUBxelwT57jsQ/giphy.gif

  • Clary

    HAAA!! So I was RIGHT! 747 IS the fattest bear!! He should have won.

    • Sagebrusher

      Biggest and heaviest is not the same as fattest. A 300 pound 5 foot kid is fatter than a 300 pound 7 foot basketball player.

  • Jean C Smith

    Non-invasive techniques like this are the wave of the future. Tranquilizing and handling a bear, or any animal, is stressful to them, to say nothing of the stress to the handlers

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  • mdfield1

    EXCELLENT article! Imagine the number of salmon these bears have to eat to attain these figures!!

    • https://fitznaturalist.com Mike Fitz

      These bears probably eat thousands of kilograms of salmon per year. A blog post I wrote last year explains a bit more and how scientists were able to estimate how much salmon bears on Kodiak Island consumed. https://blog.explore.org/how-many-salmon-will-a-bear-eat/

  • Bell

    Amazing!..thank you for the info!!..We all get a better perspective on how big these beautiful brown bears are :)

  • Karlab

    Dr. Mike, I know that length and width won’t tell the whole story about degree of fatness, but…if you were to see a known non-bear object next to one of these big bears (like a human or a black bear) how would they compare? It’s hard to gauge relative size if you’re not lucky enough to see them in person. I was trying to work out the three dimensions that you’d multiply to get these square footage numbers, but failed to get what seemed like sensible results.I

    Thank you for all you do!

    Karla B
    Big Bear fan

    • https://fitznaturalist.com Mike Fitz

      747 would basically fill up the entire rear seating area of a four door sedan. Of course, that’s if he could be molded into such a shape. He’s probably close to 7 feet long from head to tail and 5 foot tall at the shoulders.

      • Karlab

        Wow. I knew he was big, but…that’s a lot o’ bear!

        Thank you!

  • labman

    Hi Mike. This is really cool technology. Thanks for sharing the findings with us. We knew several pushed 1000 lbs but 747 at 1400 is astounding! I haven’t seen Otis lately but I would have expected him to be over 1000. He is getting older and I hope he’s getting enough calories to get him through the winter. Thanks again for some terrific information. “Wow” does not fully describe the technology!

  • Cathy Weyant

    I read this earlier.. but always worth reading again.. I say that’s everything with Explore, they’re like an old classic movie… can watch over and over and still never disappoints

  • joel cusick

    Hi Mike,
    We were fortunate to have a professional survey magazine – xyHt pick up the story. Page 28 of the January 2020 article is now onliine.

    See http://bt.e-ditionsbyfry.com/publication/?i=642307&p=30#{%22page%22:%2230%22,%22issue_id%22:642307,%22publication_id%22:%2236207%22}