Abstract:
The Antarctic Pack Ice Seal (APIS) Program
was initiated in 1994 to estimate the abundance of four
species of Antarctic phocids: the crabeater seal Lobodon
carcinophaga, Weddell seal Leptonychotes weddellii, Ross
seal Ommatophoca rossii and leopard seal Hydrurga leptonyx
and to identify ecological relationships and habitat
use patterns. The Atlantic sector of the Southern Ocean
(the eastern sector of the Weddell Sea) was surveyed by
research teams from Germany, Norway and South Africa
using a range of aerial methods over five austral summers
between 1996–1997 and 2000–2001. We used these
observations to model densities of seals in the area, taking
into account haul-out probabilities, survey-specific sighting
probabilities and covariates derived from satellite-based ice
concentrations and bathymetry. These models predicted the
total abundance over the area bounded by the surveys
(30 W and 10 E). In this sector of the coast, we estimated
seal abundances of: 514 (95 % CI 337–886) 9 103 crabeater
seals, 60.0 (43.2–94.4) 9 103 Weddell seals and
13.2 (5.50–39.7) 9 103 leopard seals. The crabeater seal
densities, approximately 14,000 seals per degree longitude,
are similar to estimates obtained by surveys in the Pacific
and Indian sectors by other APIS researchers. Very few
Ross seals were observed (24 total), leading to a conservative
estimate of 830 (119–2894) individuals over the
study area. These results provide an important baseline
against which to compare future changes in seal distribution
and abundance.
