Winter dispersal of leopard seals (Hydrurga leptonyx): environmental factors influencing demographics and seasonal abundance

Abstract

The dynamics of leopard seal Hydrurga leptonyx abundance and residency were investigated both within and between years at Bird Island, South Georgia, using observations of tagged and untagged individuals. Seals belonged to an open population, and were sampled outside the breeding season and during their northward winter dispersal (April–October). Seals at Bird Island were highly transient (41–63%) with only a limited number of individuals making repeat visits across years. A minimum yearly survival for resident seals was estimated to be between 0.61 and 0.85. The physical environment played an important role in leopard seal abundance, with observations following an apparent 4-year periodicity consistent with the frequency and timing of the Antarctic Circumpolar Wave. Years of low sea-surface temperature (SST) and extensive pack-ice corresponded to a higher number of seals present, earlier arrivals, and longer periods of residency. Peak leopard seal arrivals at Bird Island corresponded to periods of low SST, which was consistent with the pagophilic nature of this species.