Density of pack-ice seals and penguins in the western Weddell Sea in relation to ice thickness and ocean depth

Aerial band transect censuses were carried out parallel with ice thickness profiling surveys in the pack ice of the western Weddell Sea during the ISPOL (Ice Station POLarstern) expedition of R.V. Polarstern from November 2004 to January 2005. Three regions were surveyed: the deep sea of the Weddell Sea, a western continental shelf/slope region where R.V. Polarstern passively drifted with an ice floe (ISPOL), and a northern region (N). Animal densities were compared among regions and in relation to bathymetry and ice thickness distribution. Crabeater seals Lobodon carcinophaga were the most abundant species in all three regions. Their density was significantly lower in the deep sea (0.50 km−2) than in the ISPOL (1.00 km−2) and northern regions (1.21 km−2). Weddell seals Leptonychotes weddellii were not sighted in the deep-sea region, their density elsewhere ranging from 0.03 (N) to 0.08 km−2 (ISPOL). Leopard seals Hydrurga leptonyx were observed in all three areas, but could only be quantified in the deep-sea (0.05 km−2) and northern regions (0.06 km−2). The abundance of emperor penguins Aptenodytes forsteri was markedly higher in the northern (0.75 km−2) than in the ISPOL (0.13 km−2) and the deep-sea region (not quantified). Crabeater seal density was significantly related to ocean depth and modal ice thickness.