Between the 1970s and 2000, the western population of Steller sea lions experienced a population decline of over 75%, dropping by at least 170,000 animals according to NOAA’s stock assessments. This dramatic decline made it clear to scientists that there was an urgent need for long-term research and monitoring of this important marine mammal species.
Researchers from across the state of Alaska and beyond needed a way to identify and monitor the Steller sea lion populations over time and follow individual animals for their entire lives. So, in 1976, scientists began the first large-scale Steller sea lion branding project in Alaska as a critical step in long-term monitoring efforts.
With the permanent markings from branding, scientists can gather information about individuals in a population over their whole lives through re-sightings, and importantly, the brands can be observed from a distance, allowing scientists to make observations without disturbing the animals. Branding has allowed scientists to uncover subtle but important shifts in sea lion population dynamics, reproduction patterns, and geographic use that directly affect how these animals are managed under federal law.
If you’re a fan of our Chiswell Island Research Project, you know that our scientists have been monitoring the Steller sea lion population for over 25 years using remotely controlled video cameras stationed on the rookery and operated here at the Alaska SeaLife Center. By watching through remote cameras, researchers are able to closely study these endangered animals with minimal disturbance.
To identify individuals over the years, our team relies on two main tools: natural markings and brands. Natural markings, such as scars, flipper shapes, or fungal patches, help us recognize hundreds of sea lions that haul out on Chiswell Island each pupping season. But, from afar, these natural markings can be difficult to see, and our remote video monitoring is currently limited to one rookery. That’s where brands give us an extra layer of powerful insight.
Brands are permanent markings that allow scientists to track the life history of specific animals from birth, creating a timeline that natural markings alone can’t provide. Each branded sea lion becomes a living record, teaching us about survival, movements between haulouts and rookeries, age at first pupping, and even maternal success across generations.
Take female E268 as an example. She was branded as a pup in 2016, and since then, our team has documented her return to Chiswell Island year after year. Because of her brand, we know exactly where and when she was born. We’ve been able to watch her grow from a pup into a mother and have recorded her first two pups born on the island in 2024 and 2025. For females without brands, their early lives are often a mystery, as researchers typically only start collecting information once they appear on the island for their first pupping season.
Brands are visible from a distance throughout an animal’s life, allowing researchers to detect large-scale trends that would otherwise go unnoticed. By combining the small-scale observations collected with remote monitoring on Chiswell Island with the population-wide monitoring made possible by tracking branded animals across broad temporal and spatial scales, researchers can build a richer, more accurate understanding of this endangered population that we could not achieve with identifying them by natural markings alone.
While the remote video system on Chiswell Island is unique to the Steller sea lion research at the Alaska SeaLife Center, the use of brands to identify individual animals is not. Brands are a key tool used by many research programs to understand Steller sea lions across their entire range, providing a reliable and permanent way for scientists to recognize individuals no matter where they are sighted, from remote islands in Alaska to haul-outs across the Pacific Northwest.
Branding Travels Beyond Barriers
Historically, Steller sea lion management in the U.S. has divided the population into two distinct population segments (DPS): the Western and Eastern DPS. In 1997, the National Marine Fisheries Service reclassified the Western DPS from threatened to the more severe status of endangered under the Endangered Species Act. On the other hand, the Eastern DPS remained in the threatened category until 2013 when it was considered recovered and removed from the Endangered Species List. As a result, the Western DPS receives more intense conservation efforts, such as fishery management, continued monitoring and modeling, and broader research efforts.
Within these populations, several important rookeries have been identified and given an identifying letter or symbol. Each Steller sea lion that was branded was given a letter or symbol for their birth site and an identifying number. For example, Steller sea lion E268 was born at Chiswell Island in 2016, given the letter “E” as a rookery identifier, and is individually recognized by the number 268.
From 2000-2014, there were 30,518 photo-confirmed resightings of the branded Steller sea lions, allowing scientists to follow their movement and gain new understandings of boundaries between population segments and what might be driving movement.
With data from branded individuals, researchers found that two rookeries near the boundary between populations, Graves Rocks and White Sisters, have become a mixing zone, where Steller sea lions from the endangered Western DPS are now giving birth alongside Eastern DPS animals, despite being managed as separate populations under federal law. Western DPS sea lions travelling, living, or reproducing in EDPS territory may not receive appropriate protection since that region does not have the same strict management, highlighting the importance of long-term monitoring to ensure that this endangered population receives the protection it needs.
Additionally, tracking of branded individuals has shown that males, regardless of stock, often travel over a wide range, sometimes making round trips of several thousand kilometers in a single year.
One standout example is male E240, born and branded on Chiswell Island in 2016. Over the years, he has turned up in unexpected places. His branding has allowed him to be identified in various places across Alaska: from Granite Cape in Kenai Fjords National Park and Round Island in Bristol Bay all the way to Punuk Island in the Bering Strait. He was spotted on Punuk Island only six weeks after being seen more than 1,200 miles away on Chiswell Island in the Gulf of Alaska. Despite his far travels, E240 continues to return to Chiswell in the summer breeding season, most recently in 2024. While he has not yet claimed a breeding territory, researchers are watching closely, as he may be on the cusp of reaching that stage in the coming years.
Why Branding?
Between the first large-scale Steller sea lion branding project in Alaska in 1976 and the most recent brandings in 2018, thousands of Steller sea lions have been branded for research. Throughout the branding process, all efforts were made to minimize pain and stress to the animals by lowering total handling time and following published best practices. Teams relied on highly trained animal care, research, and veterinary professionals who are committed to the well-being of every animal during this process.
While branding is not the only way scientists can identify animals, to complete long-term studies on Steller sea lions, scientists need a way to confidently observe the same individual animals over their lifetimes. It is difficult to recapture Steller sea lions and other pinnipeds throughout their lives, so it is essential to have a marking that is recognizable and clearly identifiable from a distance and does not require re-marking.
Some permanent methods, like tattooing, flipper tagging, and passive integrated transponder (PIT) tags, require recapture or close observation to detect and interpret the mark. To limit stress from subsequent recapture or disturbance, branding has become an essential method for long-term research efforts.
For the branding of Steller sea lions, scientists in Alaska have found hot branding to be the best method of creating these permanent, uniquely identifiable, large marks. Hot branding is very similar to that used in the cattle industry and works by using super-heated metal to quickly burn a mark into the skin of the animal, causing scar tissue to form and creating a permanent mark. Hot branding is preferred over freeze branding because it can be done more easily on remote rookeries, produces more reliable permanent marks, and can cause less prolonged stress to animals. Freeze branding requires bulky coolants, can fade as the skin heals, and may cause more stress for animals as it takes much more time to apply and thaw.
Studies have found that the brands have minimal effects on the animal’s activity and behavior during and after the healing process, and when applied at a young age, branding has been found to have no significant impact on the pup’s survival.
Through this research, scientists gain knowledge that is vital for the future conservation of Steller sea lions, while having little lasting effect on the individual animals themselves.
Although branding on many of the Steller sea lions currently being studied was completed over 10 years ago, resightings of branded animals remain crucial to research and conservation efforts happening to this day. Each sighting of a branded animal adds another piece to the puzzle, and even casual observations from people on the water can help scientists track where these animals go and how they survive.
You can help advance research – if you see a branded sea lion, report it!
Each year, thousands of people explore Seward and other Alaskan towns, often taking to the water on wildlife cruises. If you spot a branded sea lion, whether you’re visiting or local, snap a photo. Your photos could help scientists get a more complete picture of where these sea lions travel and spend time. When taking the photos, try to show the entire animal and the full brand. You may need to take several photos to capture the entire brand. If you look back on the photos and realize you didn’t get the full brand, still send it in as partial brands may still be useful. Make sure to note the date and location where you observed the animal.
Send date, location of observation, and photos to:
akr.prd.sealions@noaa.gov and dfg.dwc.sealions@alaska.gov
Although citizen sightings and photos are helpful to researchers, be sure to give the animals ample space while capturing images. Under the Marine Mammal Protection Act, it is unlawful to harass sea lions, including acting in a manner that disrupts their normal behavioral patterns. Sea lions can be easily disturbed, be sure to maintain 100 yards or more from them and approach from downwind. If you are unsure if you are too close, give them extra space.
Interested in diving deeper? Check out these resources:
Read the results from a branding study:
Learn more about the branding process:
Hot Branding: A Technique for Long-term Marking of Pinnipeds
Learn more about Steller sea lion conservation management:
https://www.fisheries.noaa.gov/s3/2024-12/2023_SAR_Steller_Sea_Lion_Western_Stock.pdf
Check out the ASLC on Facebook, Instagram, and YouTube to see our weekly updates from the Chiswell Island Steller Sea Lion Monitoring Team from this summer.
Photographs taken by Chiswell Island Steller Sea Lion Remote Video Monitoring Research team and partners permitted by
USFWS Permit M-334-AM NOAA/NMFS #27408
This research was conducted under federal permits to the Alaska SeaLife Center: NMFS Permit No. 22293 and earlier versions for research on Endangered Steller sea lions, and USFWS Special Use and Right of Way Permits to conduct research on islands of the Alaska Maritime National Wildlife Refuge. Sponsorship was provided by the Federal Government with a grant from the National Oceanic and Atmospheric Administration – Award ID No. NA22NMF4370355.
