Many nature lovers are familiar with California sea lions, especially if they live along or visit the U.S. West Coast. These animals have become familiar sights in beach towns and even cities: the California sea lions on San Francisco’s Pier 39 are a popular tourist attraction.
But there is another sea lion found along North America’s coasts. And, in many places, it’s facing startling declines. Let’s take a look at this animal and what we can do to help.
The Steller sea lion puts the “lion” in sea lion. They don’t bark; instead they have a deep roar. Adults have a tawny colored coat. And males have long, thick hair on their head like a mane. A contender for “king of the Arctic”, the male Steller sea lion can be as heavy as 2,400 pounds and as long as 11 feet – larger than some cars!
Despite their prowess, the western population of Steller sea lions in Alaska’s western Aleutian Islands is in a steep decline – the population has plummeted by 94% in the last 30 years. And scientists aren’t yet sure what is causing the decline.
It’s not easy to study western Steller sea lions in Alaska. Their remote home is only accessible to researchers to survey in person via research vessel or by plane once (in the summer) each year or rarely twice (when there’s a very warm fall).
To learn more, a team of researchers from NOAA Fisheries led by Tom Gelatt has been deploying camera traps that capture images on the beaches where Steller sea lions haul out during the daytime (they hunt at night). Photographs from these cameras let scientists know what’s happening throughout the year.
With 20 cameras scattered around 6 sites, they are now capturing almost 400,000 images a year. That’s a lot of images to go through – more than a small team of researchers can manage. They’re asking for your help to identify images through Steller Watch, a citizen science project on the Zooniverse platform led by NOAA Fisheries biologist Katie Sweeney.
Seeking the Causes of Decline
Not all populations of Steller sea lions have been affected equally by the decline. The eastern population (southeast Alaska and down the west coast to California) have rebounded and were removed from the Endangered Species Act threatened listing in 2013. The western population (from just east of Prince William Sound and to the Aleutian Islands) threatened listing was elevated to “Endgangered” in 1997 because of continued decline.
Within this western population, the eastern portion (east of Samalga Pass) began to rebound in 2003. West of Samalga Pass is where the population continues to decline.
The difference in populations gives scientists a valuable opportunity to study differences and narrow down the cause of decline. Some of the questions that the scientists working on Steller Watch hope to answer are: What are the movement patterns? What are the birth rates and survival rates in different areas? Are there differences in movement patterns or survival by sex or by age?
“We will be able to rule out possible causes with the information we gather from this project,” Sweeney says. “One theory we are considering was predation from killer whales. There’s no doubt this happens, but there are plenty of killer whales in areas where the population is doing well.”
You will see that some of the sea lions in the images have been marked (by branding that has been well studied and does not have a long-term impact on sea lion health) so that they can be tracked individually – providing better information on dispersal (when sea lions born in one colony leave, what colonies do they travel to?) and natality (how many pups does an average individual female have over the course of her life?).
One theory that’s still under consideration for the decline is that it could be related to birth rate in the western population.
“Some females are having a pup every other year and keeping their juveniles with them for two years,” Sweeney notes.
That’s concerning because, even though juveniles in various colonies have been recorded staying with their mother and suckling for up to three years, in areas where the population is doing well, most pups wean by the end of their first winter. This gives their mother a chance to reproduce again the next year.
Steller sea lions are also threatened by boat strikes, pollutants, habitat degredation, illegal hunting and offshore oil exploration. The impact of each of these threats is poorly understood.
As you watch the cameras you may also see the impacts of marine debris and fishing gear on individual sea lions. Though some animals are able to recover from fishing gear related injuries and entanglements, an unknown number are killed at sea.
“One really impactful thing people can do for Steller sea lions is participate in ocean clean up,” Sweeney says. “Plastics in the ocean are a huge problem not just for marine mammals but for fish.”
The citizen science project is one important component of the research into the cause of the decline. You can learn more about work undertaken during the field survey like aerial population surveys and collecting sea lion poo in this story map and on the Steller Watch blog or ask the biologists a question.
Stellar Steller Sea Lions
Steller sea lions are pinnipeds, a sub-group of carnivorous marine mammals that are known for their distinct fin-feet. Like all sea lions, Steller sea lions are most easily differentiated from another pinniped group, seals, by their small ear flaps.
In the water, sea lions propel themselves with their front flippers while steering with their hind flippers. On land, they walk with all four flippers by pulling their hind flippers under their body and they are surprisingly adept at climbing cliff faces.
Steller sea lion females are smaller than the massive males but still large at nearly 800 pounds and 9 feet long. They don’t have a mane, but they do have a golden to reddish colored coat.
Females begin breeding at about age four – males take a little longer to mature, entering the competition for females when they are about seven to nine years old. Males fight and can seriously injure one another for the rights to a territory and a “harem” of females to breed with. It is stiff competition and most males don’t successfully breed until they are closer to 11 or 13 years old.
Once a male is successful in gaining a territory, he defends it with his life and may not leave the site throughout the breeding season – that can be three months without food. It’s a good thing they have a lot of blubber to keep them warm and provide energy when they are fasting.
“Steller sea lions are similar to other seals or sea lions in that they have delayed implantation,” Sweeney explains. “Their actual pregnancy is only about 9 months, but they breed once a year in summertime and once an egg is fertilized they delay implantation for a couple months to align giving birth in the summer, which is the best time to raise pups.”
Newborn pups are dark brown with a thick fur coat that sheds and gets progressively lighter until their adult coat grows in.
The sea lions feed at night and sleep most of the day. Their diet is made up of about fifty species of fish and other sea creatures including octopus and squid. They can dive up to 1,500 feet, though most of their prey are found closer to 650 feet deep.
Sea lions don’t migrate, but they do change their favorite “haul-out” seasonally to be close to abundant prey or to find better shelter in the winter. That is why you will sometimes see blank images in Steller Watch – the project’s cameras are focused on breeding beaches that may not be used in other seasons.
Even young sea lions can swim up to 75 miles without stopping to reach a new haul-out. Sea lions don’t necessarily stay in the region where they were born; some have been documented dispersing more than a thousand miles over the course of a lifetime.
There are over 300 Steller sea lion haul-outs along the North Pacific rim from Japan all the way up around and down to California. If you’re interested in seeing a Steller sea lion, try visiting an area along the coast of Oregon where you can see a haul-out (usually on an island where access is limited) from the shore or by boat like Oregon Islands National Wildlife Refuge or Three Arch Rocks National Wildlife Refuge.
Get Involved in Steller Watch
There are two options for participating in Steller Watch: You can mark photos for presence or absence of Steller sea lions or you can indicate the presence of marked individuals. Both options are easy, have a quick tutorial to get you started, a field guide with some more detail, and take no more than a few minutes. I recommend starting with the presence or absence protocol, which only takes a few seconds per image and gives you a general sense of what to expect in the images very quickly.
Then you can move on to the presence of marked animals protocol, which takes a little more time and some use of the image zooming options to check whether you can see the marks on the sea lions.
Researchers already have 750,000 images for users to classify and they expect to come back from their next expedition with about 800,000 more. They’ll be adding them to the project over time in groups of about 75,000. They will put the project on hold through the months of June and July while the researchers are out doing field science, but Steller Watch will be back again in August.
“We’re excited at how successful it’s been so far,” Sweeney says, “and how many people are engaged. We’re so happy and thankful that people are willing to participate.”
* 4/3/17 After publication, this post was edited for clarity on the location of the population that is still endangered and on the certainty with which theories of decline can be ruled out based on the current evidence.