Line transect survey of crabeater seals in the Amundsen-Bellingshausen Seas, 1994

Estimates of the population density of crabeater seals (Lobodon carcinophag us) range from 7 to 11 million, and a recent decline has been proposed. To assess the status of this and other pack-ice seal species, standardized and cost-efficient survey methods are required. We conducted a survey of Antar ctic seals concurrent with an oceanographic cruise of the R/V Nathaniel B. Palmer in the pack-ice regions between McMurdo Station, Antarctica (77 degr ees 50'S 166 degrees 45'E) and the Antarctic Peninsula (65 degrees 35'S 64 degrees 46'W) during February to April 1994. We tested the feasibility of u sing traditional methods and modern software to survey seals opportunistica lly in heavy pack-ice. We used line transect methods and the computer progr am DISTANCE to estimate crabeater seal density, and we chose uniform/cosine models to fit the detection functions. We found the detection functions fo r individuals and groups of seals to be slightly different, suggesting a si ze-bias in detection. We estimated crabeater seal density as 0.76/km(2) aft er using published values to correct for differences in sightability caused by daily activity. The methods used were compatible with interdisciplinary research incorporating daily movements through the pack-ice and could be u seful for further research into line transect sampling of pack-ice seals.