Foraging behaviour in two Antarctic fur seal colonies with differing population recoveries

Abstract

We compared Antarctic fur seals Arctocephalus gazella breeding at 2 contrasting sites on South Georgia: one high density colony at Bird Island and one lower density colony at Cooper Bay. The population at Cooper Bay was considerably smaller than that at Bird Island despite ample suitable breeding area being available. At Cooper Bay, female seals were longer but weighed less than those breeding at Bird Island and, whilst both maintained the same rate of female pup growth, male pups grew faster at Cooper Bay. Although Bird Island seals dived deeper, they dived less often than Cooper Bay seals so that both populations spent comparable amounts of time in the bottom phase of dives actively foraging. Longer distance oceanic foraging trips that were observed at Bird Island were almost entirely absent from Cooper Bay. Both populations fed on Antarctic krill, but there was an absence of myctophid prey in the diet of seals at Cooper Bay. Evidence suggests that the favoured myctophid prey of fur seals at South Georgia, Protomyctophum choriodon, are absent from the colder waters around the south-east of the island. We propose that, if these energy-rich prey are unavailable in this region then seals at Cooper Bay may find it hard to offset the increased costs of foraging trips with longer duration and distance. This potentially reduced niche width means that the Cooper Bay population may be less buffered against environmental variability. Although food resources appeared to be sufficient during the period of our study, the south-eastern region of South Georgia has increased variability in food resources that, coupled with a smaller area in which to forage, might explain the reduced population size compared to the north-eastern end of the island.

Preliminary assessment of the foraging behaviour and population dynamics of a cryptic population of the endangered New Zealand sea lion

“…For Antarctic fur seals (Arctocephalus gazella), intraspecific variation in foraging behaviour has been linked to population dynamics (Staniland et al 2010(Staniland et al , 2011. Antarctic fur seals appear to have a reduced niche width available at the southeast end of Bird Island, South Georgia, due to local bathymetry (Staniland et al 2010(Staniland et al , 2011). This appears to reduce the ability of these central place foragers to alter their foraging behaviour during periods of environmental variability, reducing the population size and growth rates relative to individuals living elsewhere …”

“…on the island (Staniland et al 2011). Similarly, Antarctic fur seals that breed on Heard Island (southwest of Australia) carry out deeper dives than fur seals from northern Bird Island.…”

At-sea behaviour of three krill predators breeding at Bouvetøya—Antarctic fur seals, macaroni penguins and chinstrap penguins

“…When data was explored based on time of day (GMT), all of the TDR records were included. A depth of 4 m was set as a minimum for classification of a dive to avoid including surface travelling or resting as diving (Waluda et al 2010, Staniland et al 2011. Sea-surface temperature (SST) was taken as the temperature recorded by the TDR at the beginning of each dive.…”

Foraging Behaviour of Juvenile Female New Zealand Sea Lions (Phocarctos hookeri) in Contrasting Environments

“…resource availability) has been observed in many taxa, including rodents [4], [5], carnivores [6], [7] and ungulates [8], [9]. Investigating this plasticity allows us to understand species-specific responses to changing environments [10]. Hence, geographic comparisons across populations of the same species in different environments are useful in defining the degree of adaptation and in characterizing the range of behavioural traits [11].…”