Pacific Walrus Population Estimation

There have been 4 previous attempts to estimate the size of the Pacific Walrus population by the U.S. and former U.S.S.R. in 1975, 1980, 1985, and 1990 but because of the vast and poorly accessible range of the population, its highly aggregated distribution, and problems with extreme detection biases, none of these efforts provided reliable population estimates.  The current size of the Pacific walrus population is unknown (USFWS Alaska stock assessment report).  This project is a collaborative effort between USGS, USFWS Office of Marine Mammal Management, and the Russian agencies GiproRybFlot and ChukotTINRO to develop and integrate new thermal infrared scanner, high resolution digital photography, and satellite radio telemetry technologies to overcome previously insurmountable obstacles and provide the first reliable estimate of this population's size. We are developing a method that uses high altitude infrared imaging to detect walrus groups hauled out on sea ice, high resolution digital photography of a subsample of the detected groups to estimate the number of walruses per detected group, and satellite radio telemetry of individual walruses to estimate the proportion of the population available to be detected by the scanner (walrus tagging). The new survey method offers the potential to provide the first reliable estimate of this internationally important population by integrating technologies that allow coverage of a much larger portion of the range and more accurate enumeration of groups than was previously possible and for the first time, accounting for the proportion of the population not available to be detected.

References

Douglas, D. C., M. S. Udevitz, J. R. Gilbert, and D. O. Hunter. 1991. Evaluation of airborne videography for enumerating Pacific walruses (Odobenus rosmarus divergens) on sea-ice haulouts. Pages 507-513 in Proceedings of resource technology 90, international symposium on advanced technology in natural resource management. American Society of Photogrametry and Remote Sensing, Falls Church, Virginia.

Udevitz, M. S., J. R. Gilbert, and G. A. Fedoseev. 2001. Comparison of methods used to estimate numbers of walruses on sea ice. Marine Mammal Science 17(3):601-616.

Burn, D. M., M. A. Webber, and M. S. Udevitz.  2006.  Application of airborne thermal imagery to surveys of Pacific walrus.  Wildlife Society Bulletin 34(1):51-58.