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Results and evaluation of a survey to estimate Pacific walrus population size, 2006

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Full Publication: https://doi.org/10.1111/j.1748-7692.2010.00419.x

Product Type: Journal Article
Year: 2011

Authors: Speckman, S. G., V. I. Chernook, D. M. Burn, M. S. Udevitz, A. A. Kochnev, A. Vasilev, C. V. Jay, A. Lisovsky, A. S. Fischbach, and R. B. Benter

Suggested Citation:
Speckman, S. G., V. I. Chernook, D. M. Burn, M. S. Udevitz, A. A. Kochnev, A. Vasilev, C. V. Jay, A. Lisovsky, A. S. Fischbach, and R. B. Benter. 2011. Results and evaluation of a survey to estimate Pacific walrus population size, 2006. Marine Mammal Science 27(3):514-553. doi:10.1111/j.1748-7692.2010.00419.x

Abstract


In spring 2006, we conducted a collaborative U.S.-Russia survey to estimate abundance of the Pacific walrus (Odobenus rosmarus divergens). The Bering Sea was partitioned into survey blocks, and a systematic random sample of transects within a subset of the blocks was surveyed with airborne thermal scanners using standard strip-transect methodology. Counts of walruses in photographed groups were used to model the relation between thermal signatures and the number of walruses in groups, which was used to estimate the number of walruses in groups that were detected by the scanner but not photographed. We also modeled the probability of thermally detecting various-sized walrus groups to estimate the number of walruses in groups undetected by the scanner. We used data from radio-tagged walruses to adjust on-ice estimates to account for walruses in the water during the survey. The estimated area of available habitat averaged 668,000 km2 and the area of surveyed blocks was 318,204 km2. The number of Pacific walruses within the surveyed area was estimated at 129,000 with 95% confidence limits of 55,000 to 507,000 individuals. This value can be used by managers as a minimum estimate of the total population size.

(Russian version - 2.3 mb pdf)

Keywords: Pacific walrus, thermal imagery, abundance, detection

Annotation


Sound assessments of population status are important for the international management of Pacific walruses. The methods in this study provide useful tools and techniques for surveying large swaths of walrus territory. The population estimate of 129,000 with 95% confidence limits of 55,000507,000 individuals likely represents the number of Pacific walruses within about half of potential walrus habitat, since poor weather conditions precluded surveying in other areas.