Mystery in Alaska:
Why Have All the Sea Lions Gone?
by
Frank J. Dinan, Thomas R. Stabler, and Renee A. Larson
Department of Chemistry and Biochemistry
Canisius College, Buffalo, NY
by
Frank J. Dinan, Thomas R. Stabler, and Renee A. Larson
Department of Chemistry and Biochemistry
Canisius College, Buffalo, NY
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 85–90% decrease in the abundance of these creatures; this region contains the Western stock of Steller sea lions, as illustrated in Figure 1. The Eastern stock, also seen in Figure 1, is located on the southeast coast of Alaska and its Steller sea lion population is increasing modestly (Figure 2).
Figure 1. Distribution (Click for enlargment.)
Figure 1 courtesy of the Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration (NOAA).
Figure 2. Steller Sea Lion Populations
Estimated numbers of Steller sea lions (all ages) in Alaska from 1956 to 2000 (from Trites & Larkin, 1996; A.W. Trites, unpublished data). Figure used with permission of the North Pacific Universities Marine Mammal Research Consortium.
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 8 years of age and in females at an average age of 4.6 years (Pilcher, 1981). 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.
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?
Date Posted: November 3, 2009.
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