Featured Image Credit: Colby Stopa
By Eva Gruber
Steller sea lions (Eumatopias jubatus) are the largest of the eared seals, with males reaching masses of up to 2,400 pounds, and females up to 800 pounds. They reside in the Pacific Ocean, hauling out on islands from Russia’s Commander Islands, east along the Aleutian Chain, and down south all the way to California’s Channel Islands. Despite this large range, they have experienced significant declines in their population, with the low point in 2003. Since then, it has been steadily increasing 1.7% a year, but still remains low and much lower than their historical numbers.
Marine biologists in Alaska, and at the Alaska Fisheries Science Center in Seattle, have been closely monitoring Steller’s sea lion populations for years now. Part of the work involves going out to their remote island breeding locations and marking individuals so that they may be identified and followed throughout their life. This allows scientists to better understand their natural history, along with their reproductive success, longevity, and life habits.
Recently, after years of gathering such data, a report was published in PLOS ONE, a very reputable open access science journal. The authors studied the movement patterns of 369 female Steller sea lions that had been tagged in 2001, allowing them to follow their movements from 2001 to 2015.
This study revealed that 97% of the female Steller sea lions were natally philopatric – they returned to breed in the same area that they were born. When the females did switch breeding sites, they did not go far – choosing instead to remain close to where they were born, and choosing sites that already had large numbers of fellow sea lions.
This is a basic result of direct science that has significant implications in better conserving the species. Knowing their range and their breeding grounds allows scientists to better track their population, and any changes that might occur.
The fact that females are natally philopatric might suggest their familiarity with the area where they were born, making it easier for them to forage successfully and increasing their fecundity and longevity. Since they are social animals, it might also represent familiarity with neighboring sea lions. Preserving these areas for Steller sea lions is the key to protecting the species and helping bring them back from the threat of extinction.
If you would like to take part in helping track tagged Steller sea lions, you can engage in a wonderful citizen science project that the Alaska Fisheries Science Center is leading. Steller Watch shows you pictures taken by remote cameras set at rookeries in the Aleutian Islands (where Steller populations have dropped by as much as 94 percent) and asks you to identify marked seals. This is a wonderful way to contribute to conservation and research in an endangered marine mammal species!