Antarctic Science

Life Sciences

Estimating population status under conditions of uncertainty: the Ross seal in East Antarctica

Colin J. Southwella1 c1, Charles G.M. Paxtona2, David L. Borchersa2, Peter L. Bovenga3, Erling S. Nordøya4, Arnoldus Schytte Blixa4 and William K. De La Marea5

a1 Department of the Environment and Water Resources, Australian Antarctic Division, Channel Highway, Kingston, TAS 7050, Australia

a2 School of Mathematics and Statistics, University of St. Andrews, North Haugh, St Andrews KY16 9SS, UK

a3 National Marine Mammal Laboratory, 7600 Sand Point Way NE Seattle, WA 98115, USA

a4 Department of Arctic Biology, University of Tromsø, N-9037 Tromsø, Norway

a5 CSIRO Marine and Atmospheric Research, Cleveland Laboratories, PO Box 120, Cleveland, QLD 4163, Australia

Abstract

The Ross seal (Ommatophoca rossii) is the least studied of the Antarctic ice-breeding phocids. In particular, estimating the population status of the Ross seal has proved extremely difficult. The Protocol on Environmental Protection to the Antarctic Treaty currently designates the Ross seal as a ‘Specially Protected Species’, contrasting with the IUCN's classification of ‘Least Concern’. As part of a review of the Ross seal's classification under the Protocol, a survey was undertaken in 1999/2000 to estimate the status of the Ross seal population in the pack ice off East Antarctica between 64–150°E. Shipboard and aerial sighting surveys were carried out along 9476 km of transect to estimate the density of Ross seals hauled out on the ice, and satellite dive recorders deployed on a sample of Ross seals to estimate the proportion of time spent on the ice. The survey design and analysis addressed the many sources of uncertainty in estimating the abundance of this species in an effort to provide a range of best and plausible estimates. Best estimates of abundance in the survey region ranged from 41 300–55 900 seals. Limits on plausible estimates ranged from 20 500 (lower 2.5 percentile) to 226 600 (upper 97.5 percentile).

(Received December 10 2006)

(Accepted July 04 2007)

(Online publication January 04 2008)

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