For example, if walruses haul out on land in late summer, after ice-based surveys are complete, lower calf:cow ratios ICG-001 molecular weight on beaches may be a consequence of calves being exposed to a constant survival rate for a longer

period of time and not due to abnormally high mortality on beach haulouts. While the estimation of calf:cow ratios provides managers with a metric than can be used to monitor the status of the Pacific walrus population, how the ratio is sampled can and should be improved upon. Therefore, we make the following recommendations: (1) Surveys need to classify 200–300 cow groups (~1,600–2,500 cows) to estimate calf:cow ratios with 20%–30% relative precision. Higher precision will require sampling more groups and surveys conducted at a different time of

year or on beaches (i.e., not on sea ice) may require differing sample sizes. (2) Tagging studies need to be conducted to determine how the haul out behavior of cows with calves differs from that of cows without calves. Estimates of the availability of cows with calves and cows without calves can be used to estimate the true calf:cow ratio. (3) Ideally, the sizes of groups classified should reflect what is available. If observers cannot selleck kinase inhibitor ensure that the distribution of group sizes sampled approximates what is available, sampling some large groups allows investigation of how the ratio may vary as a function of group size. (4) The timing of future surveys warrants careful consideration. Although we did not detect declining ratios as a function date, ratios collected across years may not be directly comparable if they are collected at different times of year, as calf mortality may confound comparisons. (5) Surveys should cover the entire ice edge and should be repeated when possible to verify that ratios are not spatial and/or temporal anomalies. Dr. Francis “Bud” Fay began developing this method to visually sample walruses in 1958 because he recognized the need for a sensitive method for monitoring HSP90 the status of the population. He would want us to thank the officers and the crews of the survey ships

and those that assisted with the field tests, especially B. P. Kelly, A. Akeya, J. J. Burns, P. Gehnrich, S. Hills, A. Hoover-Miller, M. Iya, A. Johnson, L. Lowry, E. Miller, R. Miller, R. Nelson, G. C. Ray, D. Rugh, J. Sease, A. Sorensen, and D. Wartzok. Ship support was provided by NOAA, Greenpeace, and the Soviet All-Union Institute of Fisheries and Oceanography. Additional support was provided by the University of Alaska Sea Grant Program, the Outer Continental Shelf Environmental Assessment Program, the U.S. Fish and Wildlife Service, the Minerals Management Service, and the Alaska Department of Fish and Game. B. Bolker provided helpful discussion regarding beta-binomial models. T. Gerrodette provided a useful critique of this manuscript. M. Udevitz, D. Monson, and C.