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Can experimental manipulation be used to determine the cause of the decline of western stock of Steller sea lions Eumetopias jubatus?






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Can experimental manipulation be used to determine the cause of the decline of western stock of Steller sea lions Eumetopias jubatus?

A variety of reasons have been postulated for the decline of Steller sea lions (Otariidae: Eumetopias jubatus) in the Northeast Pacific. To date, however, it has proved impossible to distinguish among these reasons given the available data. In principle, experimental management based on spatial replication of treatments could be used to discriminate among some of these hypotheses. A simulation protocol was developed and applied to evaluate the power of a set of potential experiments to distinguish between whether the cause of the decline was fishing-induced or due to other factors. The simulations are based on an operating model that is individual-based and spatially explicit, and can be parameterized to represent the implications of a range of possible causes for the decline. This model can be used to generate the types of data typically available for the western stock of Steller sea lions. Experiments based on splitting four of the regions identified for past analyses of population dynamics in-formation into sectors that are either open to some fishing or completely closed are considered. The performance of these experiments is, however, poor, owing to the impact of movement, different historical trends in different areas, demographic stochasticity, and the likely size of the effect that the experiments are attempting to detect. These results suggest that the currently available information imply that large-scale experimental manipulation by means of additional spatial closures, where the results are analyzed by examining trends in pup counts, is unlikely to provide an effective means of discriminating among alternative hypotheses for the decline in Steller sea lions in Alaska.


Accession: 038040432



Related references

Sinclair, E.; Zeppelin, T., 2002: Seasonal diet trends among the western stock of Steller sea lions (Eumetopias jubatus). Alaska Sea Grant Report, 02-02: 53-55

Sinclair, E.H.; Zeppelin, T.K., 2002: Seasonal and Spatial Differences in Diet in the Western Stock of Steller Sea Lions (Eumetopias jubatus). We identified prey remains from 3,762 scats (feces) of Steller sea lions (Eumetopias jubatus). Scats were collected from 1990-1998 on island sites across most of the range of the United States western stock of the species. Walleye pollock (Theragr...

Sease, JL.; Gudmundson, CJ., 2002: Aerial and land-based surveys of Steller sea lions Eumetopias jubatus from the western stock in Alaska, June and July 2001 and 2002. The National Marine Fisheries Service (NMFS) conducted aerial and land-based surveys of the western stock of Steller sea lions (Eumetopias jubatus) in Alaska during June and July of 2001 and 2002 at all sites from 144deg. W to 172deg. E, the weste...

Fritz, LW.; Stinchcomb, C., 2005: Aerial, ship, and land-based surveys of Steller sea lions Eumetopias jubatus in the western stock in Alaska, June and July 2003 and 2004. The National Marine Fisheries Service (NMFS) conducted aerial, land, and ship-based surveys of the western stock of Steller sea lions (Eumetopias jubatus) in Alaska during June and July 2003 and 2004. Survey effort in 2003 consisted of sea lion pu...

Zeppelin, T.K.; Tollit, D.J.; Call, K.A., 2004: Sizes of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by the western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1998 to 2000. Prey-size selectivity by Steller sea lions (Eumetopias jubatus) is relevant for understanding the foraging behavior of this declining predator, but studies have been problematic because of the absence and erosion of otoliths usually used to estima...

Trites, A.W.; Donnelly, C.P., 2003: The decline of Steller sea lions Eumetopias jubatus in Alaska: A review of the nutritional stress hypothesis. 1. The decline of Steller sea lions Eumetopias jubatus in the Gulf of Alaska and Aleutian Islands between the late 1970s and 1990s may have been related to reduced availability of suitable prey. Many studies have shown that pinnipeds and other mam...

Burek, K.A.; Gulland, F.M.D.; Sheffield, G.; Beckmen, K.B.; Keyes, E.; Spraker, T.R.; Smith, A.W.; Skilling, D.E.; Evermann, J.F.; Stott, J.L.; Saliki, J.T.; Trites, A.W., 2005: Infectious disease and the decline of Steller sea lions (Eumetopias jubatus) in Alaska, USA: insights from serologic data. Serologic data were examined to determine whether infectious disease may have played a role in the decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands, USA. Available published data, unpublished data, and r...

Hoshino, H.; Fujita, S.; Goto, Y.; Isono, T.; Ishinazaka, T.; Burkanov, V.N.; Sakurai, Y., 2006: Organochlorines in Steller sea lions (Eumetopias jubatus) from the western North Pacific. The population of Steller sea lions, Eumetopias jubatus, has declined in the western North Pacific since the late 1960s. Recently, the Sea of Okhotsk was reported to be polluted by organochlorine contaminants (OCs) including polychlorinated biphen...

Hoopes, L.A.; Rea, L.D.; Christ, A.; Worthy, G.A.J., 2014: No evidence of metabolic depression in Western Alaskan juvenile Steller sea lions (Eumetopias jubatus). Steller sea lion (Eumetopias jubatus) populations have undergone precipitous declines through their western Alaskan range over the last four decades with the leading hypothesis to explain this decline centering around changing prey quality, quanti...

Maschner, H.D.G.T.ites, A.W.R.edy-Maschner, K.L.B.tts, M., 2013: The decline of Steller sea lions Eumetopias jubatus in the North Pacific insights from indigenous people, ethnohistoric records and archaeological data. A number of hypotheses have been proposed to explain the most recent decline (1977 2012) of Steller sea lions (SSL; Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. We examined hypotheses about fisheries competition, environmental c...