BIOLOGY 1308. The Decline of Sea Lion Population in Alaska. Mystery in Alaska. OUTLINE. I. Introduction II. Hypotheses III. Methods IV. Results V. Conclusion VI. References. The Steller Sea Lion.
The Decline of Sea Lion Population in Alaska
Mystery in Alaska
The Steller Sea Lion
The Steller sea lion is a species near extinction. The population of these species is decline every year and the reasoning behind its demise is speculated by many scientists.
Located mostly near Alaska
Favorite Fish is pollock and herring
This picture displays the range of the Steller sea lion and the rookeries they inhabit.
Hypotheses 1: The predators of the Steller sea lion were the main cause of the decline in Steller sea lions.
Hypotheses 2: Steller sea lions are undergoing nutritional stress.
The second hypothesis uses data from D.A.S. Rosen and A.W. Trites in their published journal titled Digestive efficiency and dry-matter digestibility of Steller sea lions fed herring, pollock, squid, and salmon. Our group has developed an experiment that will try to prove that the western Alaskan sea lions are nutritionally stressed due to the lack of herring and over population of pollock. This experiment will take place in a laboratory setting and contain five 300 feet deep tanks. Each tank will contain different combinations of herring, pollock, or sea lions, depending on what results need to be found. The following resources for this experiment are as follows:
Pollock vs. Herring
Pollock- large, more solitary, difficult for sea lions to catch
Herring- small schooling fish, usually fed upon in large numbers
Western Sea Lions - Percentage down drastically compared to 1970’s
1970 Federal Ban
Southwestern Alaskan resulted in less herring, more Pollock, less Sea Lions. This resulted in Higher pup mortality rate
Southeastern Alaskan waters largely unchanged
This experiment will take place in a laboratory setting and contain five 300 feet deep tanks. Each tank will contain different combinations of herring, pollock, or sea lions, depending on what results need to be found.
Experiment Tank 1 & 2
Tank 1 – Pollock Or Herring
Healthy or unhealthy statistic for Pollock (compared to general health)
Amount of energy and type of energy received from eating pollock
Toxic Readings (is the environment affect health of fish)
Depth count- How deep they dive
Experiment Tank 3
Tank 3 – Pollock and Herring-
Statistics of amount of herring eaten (Pollock eat herring)
How many pounds
Statistics of most fish eaten at what stage of life (juvenile vs. adult herring)
Tank 4 – Pollock, Herring, and Western Or Eastern Steller Sea Lions
Sea lions and Fish realeased into the sea
This data will allow to further the precision of our experiment
Pollock and salmon were the largest prey items in both length and mass. Herring had the greatest energy density, and our sea lions were unable to maintain body mass while eating squid and Pollock. Pollock have much larger, bony structures that pass undigested through the gut, compared with the smaller, delicate bones of herring and the almost completely digestible squid
According to Rosen in his study of the decline of steller sea lions, in the locations where polluck were more abundant, the fatality rate of the steller sea lion pups were much higher. Pollock are fish that are lower in quality concerning nutrients for sea lions to sustain life. The idea of sea lions to rely solely on pollock for their source of nutrition can lead to the reasoning of the shorter life of steller sea lion pups. We can see this in the research done by Trites, Calkins, and Winship. These scientist’s studies of the decline of the steller sea lions, the locations where pollock were more abundant, and the fatalty rate of the steller sea lion pups were much higher (Calkins & Winship 2007).
Discussion and Conclusion Continued
All of the scientists we studied agreed that for the most part, data to assess each of the possibilities are currently limited. Whether the decline is caused by a single factor or a combination of all of the above is a matter of scientific debate. We may never know the true cause of the decline, but every day we get closer to stopping their decline and increasing their numbers through science and research