Steller Rookery

Steller sea lion rookery.

For the last three years while assuming my role as Project Director on our Eyes on Conservation series I have been working in Alaska on a Steller sea lion survival study in the Aleutian Islands. The program is operated by NOAA’s (National Oceanic Atmospheric Association) National Marine Mammal Laboratory.

The Steller sea lion (Eumetopias jubatus) was first described in 1741 by German naturalist Georg Wilhelm Steller. He is also credited with describing the Steller’s eider, jay, sea eagle, and sea cow during his early travels in the northern Pacific Ocean. It is the largest of the eared seals, but still smaller than elephant seals and walrus. Having once roamed as far south as the Channel Islands in California to breed, the Steller sea lions’ current breeding range is protracted and only now stretches as far south as Ano Nuevo Island in California to the Gulf of Alaska and across the Bering Sea into the Sea of Okhotsk in Russia.


Adult males defending their territories.


A majority of the year is spent traveling long distances and bulking up on a variety of fish, squid, and octopus. Steller sea lions return to isolated rock islands to give birth and reproduce during the summer months. Adult males can reach up to 11 feet in length and weigh up to 2,500 pounds. Females can reach up to 9.5 feet and weigh up to 770 pounds. The males arrive at these rookeries to establish their territories prior to the females returning to give birth. Most males will fast for the entire duration of the breeding season, from May to August! As the females arrive, the males aggressively defend their home turf, an area conducive for females to rest and give birth, and eventually copulate. Females are not confined to an individual harem, but instead are free to roam around the rookery until their departure.

Pup on mom

Adult female with pup resting on top.

Females give birth to one pup a year. At birth a Steller sea lion pup is a little over 3 feet long weighs about 50 pounds. Pups are born with a black coat which will turn a brownish color after the first molt, at about 4-6 months of age. Females begin foraging trips just a few days after birth and usually wean after one year, but have been observed suckling 2 to 3 years of age. It is common for an adult female to care for two of her offspring from different years. As the pups gain weight and learn to swim, the rookery structure begins to collapse. At this time, the sea lions head back out into the ocean to recoup and prepare for next breeding season.

Ugamak Island, AK

Ugamak, Alaska.

The study site that I have been stationed at is a small uninhabited volcanic rock in the Aleutian chain called Ugamak. It is an uninhabited island about 300 feet above sea level with a significant amount of fog, wind, rain and cold temperatures. The weather can fluctuate from season to season as I have experienced, which makes this area an extremely rough location to live.

The main focus of this project is to monitor Steller sea lion populations, use the data to draw conclusions about demographics, and thus implement appropriate conservation management strategies and regulations to increase survival. Steller sea lion populations are broken up into the Asian, eastern and western stocks. The western stock is listed as endangered as its numbers have been severely declining by as much as 70-80% since the 1970s. However the eastern stock was just delisted from threatened status in 2013. Some of the threats affecting Steller sea lions include various types of fishing nets, over-fishing, ocean pollutants, habitat conversion, and illegal hunting.

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Images were collected pursuant to NMFS Permit #14326.

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