Ross seals typically haulout in dense consolidated pack ice over large geographic areas. Because these areas can usually only be reached by ice-breaking ships or long-range aircraft, it is difficult to estimate population size and trends with high certainty. Published global population estimates range from 20,000-50,000 (Scheffer 1958) up to 220,000 animals (Gilbert and Erickson 1977). However, early estimates were based on very limited sampling and were highly speculative. The most recent global estimate, from analysis of ship and aerial sighting surveys carried out around the Antarctic Continent between 1968 and 1983, provided a point estimate for global Ross seal population size in the pelagic pack ice of the Southern Ocean in the order of 130,000 animals (Erickson and Hanson 1990, Reijnders et al. 1993). No indication of the uncertainty around this estimate was given. A more recent regional survey in the pack-ice off east Antarctica between 64-150ºE indicates that broad-scale estimates are likely to have considerable uncertainty around them. The best estimates for this regional survey were in the order of 50,000, 95% confidence limits ranged from 20 000 to 227 000 (Southwell et al. 2008). Given this uncertainty, only gross changes in Ross seal population size could be confidently detected from repeated surveys.
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