Distribution, density and abundance of Antarctic ice seals off Queen Maud Land and the eastern Weddell Sea

Daniel Steinhage,Marthán N Bester,Peter Boveng,Joachim Plötz,Eliezer Gurarie,Erling S Nordøy,Michael Cameron,Horst Bornemann,John L Bengtson,Arnoldus Schytte Blix

doi:10.1007/s00300-016-2029-4

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) × 103 crabeater seals, 60.0 (43.2–94.4) × 103 Weddell seals and 13.2 (5.50–39.7) × 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.

Highlights

Ice-associated seals in Antarctica are considered to be highly abundant (Reeves and Stewart 2003), yet absolute numbers as well as ecological relationships between species and habitat remain poorly known primarily due to the logistical difficulty of studying them in their remote and inaccessible areas
Four species of seal compose the Antarctic ‘ice seals’, all members of the Lobodontini: the crabeater seal (Lobodon carcinophaga), Weddell seal (Leptonychotes weddellii), Ross seal (Ommatophoca rossii) and leopard seal (Hydrurga leptonyx). Three of these species are most strongly associated with the pack ice: the crabeater seal, the Ross seal and the leopard seal, while the Weddell seal primarily inhabits the shore-fast ice
841 (62 %) of the crabeater seals and 110 (70.5 %) of the Weddell seals were found in groups of size 10 or greater

Summary

Introduction

Ice-associated seals in Antarctica are considered to be highly abundant (Reeves and Stewart 2003), yet absolute numbers as well as ecological relationships between species and habitat remain poorly known primarily due to the logistical difficulty of studying them in their remote and inaccessible areas. We used the same haul-out model for all the German data and for the crabeater seals observed in the Norwegian and South African surveys.

Results

Conclusion