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 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 Cited: http://www.marinemammal.org/steller_sea_lion/steller_sea_lion_anatomy.php
Part I – Introduction This picture displays the range of the Steller sea lion and the rookeries they inhabit.
Where have the Steller sea lions gone? • “In 1934 Secretary of Interior J.A. King declared “It has been determined that sea lions occur in excessive numbers in the waters of Alaska and are inflicting serious economic loss on the fisheries.” [16 USC 659]. By the 1950’s localized depletion of salmon by Steller sea lions was perceived as a threat to commercial fishermen, so the state sanctioned efforts to reduce sea lion numbers. After the mid-1970’s, Steller sea lion numbers declined drastically. In the 1990’s, competition with commercial fishermen was perceived as a threat to sea lions; therefore fisheries have been managed to reduce the potential localized depletion of pollock, cod, and atka mackerel. Since the 1990’s, Stellar sea lions have been the subject of intensive conservation efforts, political and biological debate, and an unprecedented research initiative.” (Wynne, 2005)
Hypotheses 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.
Methods • We are not experts and have no prior experience scientifically studying Steller sea lions. • We have to use current scientific data from scientists in the field and our own understanding of that data to develop our results. • For our first hypothesis we used the data from Lance Barrett-Lennard’s study The impact of killer whale predation on Steller sea lion populations in British Columbia and Alaska and the study Killer appetites: assessing the role of predators in ecological communities by USC students Terrie M. Williams, James A. Estes, Daniel F. Doak, and Alan M. Springer.
Methods Continued 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 The Results: Southwestern Alaskan resulted in less herring, more Pollock, less Sea Lions. This resulted in Higher pup mortality rate Southeastern Alaskan waters largely unchanged
The Experiment 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 is needed to conduct this experiment • 7 Western Sea Lions (3 Females about to have pups, 3 pups from birth, 1 Male) • 7 Eastern Sea Lions (3 Females about to have pups, 3 pups from birth, 1 Male) • Pollock population • Herring population • Herring/Pollock food (phytoplankton) • 5 tanks • Scientific staff (scientists, marine biologist, sea lion keeper, technologist, geneticist, transportation) • Depth Readers/ Transmitters
Experiment Tank 1 & 2 Tank 1 – Pollock Or Herring Nutritional value 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 Reproduction rate
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)
Experiment Tank 4 & 5 Tank 4 – Pollock, Herring, and Western Or Eastern Steller Sea Lions • Fish Count (How much they eat) • Pollock • Herring • Diet- Check scats every month. Get enough scat material to study until next month comes around. • Amount of Herring • Amount of Pollock
Experiment Tank 4 & 5 Part 2 • Weight and Size • Male • Juvenile • Adult • Female • Juvenile • Adult • Overall health • Coat • Metabolism • Sociability (any particular sea lion lacking as part of a group) • Appetite • Genetic Testing – Just once at a certain age
Experiment Conclusion Sea lions and Fish realeased into the sea • Sea lions fitted with depth readers • Sea lions fitted with transmitters • Seasonal visits to certain locations to collect scat samples. This data will allow to further the precision of our experiment
Results • The effects of predation on a robust sea lion population (consisting of over 100,000 animals) are minimal, but with smaller populations (<50,000) the effects are more significant, and may even be sufficient to drive a population decline. The authors conclude that killer whales did not cause the sea lion decline, but may now be a significant contributing factor. The model suggests that as many as 18% of the sea lions that die each year in Alaska are taken by killer whales.” (Barett-Lennard et al. 1995)
Second Hypothesis 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
Discussion and Conclusion • The question that has been asked by many scientists is why the population of the western steller sea lion is declining while the eastern stock is increasing? This group’s hypothesis to this question is that steller sea lions are undergoing nutritional stress.
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
Summary 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
REFERENCES • Barrett-Lennard, L. G., K. Heise, E. Saulitis, G. Ellis, and C. Matkin. 1995. The impact of killer whale predation on Steller sea lion populations in British Columbia and Alaska. Report to the North Pacific Universities Marine Mammal Research Consortium, Vancouver, British Columbia, Canada. • North pacific universities marine mammal consortium : Steller sea lion biology . (n.d.). Retrieved from http://www.marinemammal.org/steller_sea_lion/decline_body.php • Rosen, D.A.S., and A.W. Trites, 2000 Pollock and the decline of Steller sea lions. Canadian Journal of Zoology 78(7): 1243-1250. Retrieved from http://www.marinemammal.org/pdfs/RosenTrites2000-digesteff.pdf
REFERENCES Continued • Rosen, D.A.S., and A.W. Trites,(2005, April 15) Examining the potential for nutritional stress in young steller sea lions: Physiological effects of prey composition. J Comp Physiol B (2005) 175: 265 273. Retrieved from http://www.marinemammal.org/pdfs/2005pdfs/Rosen_Trites_2005.pdf • Terrie M. Williams, James A. Estes, Daniel F. Doak, and Alan M. Springer, Ecology, 85(12), 2004, pp. 3373–3384, 2004 by the Ecological Society of America. Retrieved from http://www.usc.edu/org/cosee-west/PDFs/WilliamsEstesWhales04.pdf • Welch, C. (2010, August 02). With some sea-lion populations in swift decline, feds call for closing aleutian fisheries. The Seattle Times. Retrieved from http://seattletimes.nwsource.com/html/localnews/2012516711_stellersealions03m.html • Wynne, K. (2005, MAY 01). Alaskas stellar sea lions - boom to bust - and back?. Alaska seas and coast, Retrieved from http://seagrant.uaf.edu/bookstore/seasandcoasts/issues/ak-seas-and-coasts-0505.pdf