A REVIEW OF BIAS AND UNCERTAINTY IN ANTARCTIC PACK-ICE SEAL ABUNDANCE ESTIMATES

While the joint CCAMLR-IWC workshop will consider a number of parameters for species groups, including abundance, trends in abundance, habitat utilisation, foraging and growth, this review of pack-ice seals focuses primarily on abundance and to a lesser extent trends in abundance. The review addresses population surveys and abundance estimates for the four species of phocid seal commonly encountered in the pack-ice and fast-ice surrounding Antarctica (crabeater seal Lobodon carcinophaga, Ross seal Ommatophoca rossii, leopard seal Leptonyx hydrurga and Weddell seal Leptonychotes weddellii). The spatial scope covers the circumpolar extent of pack-ice, and the temporal scope spans a period of more than 50 years from when pack-ice seal surveys were first undertaken and reported in the 1950s to the present day. The review of abundance surveys is presented chronologically, and in doing so tries to provide a sense of evolution and development of methodologies over a 50 year period of application. The methodologies employed in individual survey efforts are described, and the likely biases and uncertainties in resulting abundance estimates are discussed. Abundance estimates from individual and collective survey efforts are provided. It is difficult to derive trends in abundance from these abundance estimates because there have been very few repeat surveys in the same or similar regions, methodologies have evolved and improved over time, and uncertainty around abundance estimates is substantial.