1. Overfishing of prey species: Steller sea lions primarily feed on fish such as herring, pollock, and salmon. Overfishing of these species could result in a decrease in food availability for the sea lions, particularly in the Western stock's range.
2. Pollution: Pollution such as oil spills and plastic debris can impact the sea lions directly through ingestion or entanglement, as well as indirectly by contaminating their food sources.
3. Climate change: Changes in ocean temperatures and currents can alter the distribution and abundance of prey species, making it more difficult for sea lions to find food.
4. Competition with other predators: Sea lions may face increased competition for food from other predators, such as killer whales, in certain regions.
5. Habitat loss: Destruction of sea lion habitat, such as ice floes or rookeries, could impact their ability to breed and raise their young.
The decline of the Western stock of Steller sea lions may be due to a combination of these factors that are more prevalent in their range compared to the Eastern stock's range. For example, if overfishing or pollution is more severe in the Western stock's territory, this could explain why their population is decreasing while the Eastern stock is experiencing a modest increase.
Mystery in Alaska: Why Have All the Sea Lions Gone?
Frank J. Dinan, Thomas R. Stabler, and Renee A. Larson
Department of Chemistry and Biochemistry Canisius College, Buffalo, NY
Part1-Westvs. East
Studies conducted by the Alaska Fisheries Science Center of the National Marine Mammal Laboratory have established that Steller sea lions have been disappearing at an alarming rate in Alaskan waters. Since the 1970s, these marine mammals have experienced a severe overall decrease in population, but the decrease has not been uniform. The region from the Prince William Sound through the Aleutian Islands has observed an & -90( decrease in the abundance of these creatures; this region contains the Western stock of Steller sea lions, as illustrated in Figure r. The Eastern stock, also seen in Figure r, is located on the southeast coast of Alaska and its Steller sea lion population is increasing modestly (Figure)).
Figure 1. Distribution
Steller sea lion roakeries Range of the Steller sea lion
United States
Eastern Population
Canada
China
Gulf of Alaska
144'W
Alaska (US)
Bening Sen
Western Population
Pacific Ocean
Russia
Okhotsk Sea
Nautical Miles
1,000
Uspan
0 250 500
Credits: Figurer courtesy of the Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration (NOAA). Photo of Stellar sea lions in Resurrection Bay by Frank Kovalchek, Creative Commons Attribution 2.0 License.
Figure 2. Steller Sea Lion Populations
Total population
50,000
250,000
Western stock
150,000
0
1960
1970
Estimated numbers of Steller sea lions (allages) in Alaska from 1956 to 2000 (from Trites & Larkın, 1996, A.W. Trites, unpublished data). Figure used with permission of the North Pacific Universities Marine Mammal Research Consortium.
Eastern stock
1980
1990
2000
There is particular concern regarding the Western stock of sea lion pups. Most of these juveniles don't survive more than three years and therefore many do not reach sexual maturity, which occurs in males between 3 to & years of age and in females at an average age of t., years (Pilcher, 19&r). Because of their small size, the sea lion pups are more vulnerable to changes in their environment and are less able to adapt to these changes. While they have higher energy needs for growth and development, the pups are inexperienced hunters, inefficient at catching prey, and largely dependent on their mothers for survival.
r. List several possible reasons for the decline of the Steller sea lion population.
). Can any of your reasons explain why the Western sea lion stock is decreasing and the Eastern stock is modestly increasing? If so, how?
1 answer
1 answer