The role of foraging behaviour in recovering fur seal populations

Large carnivores shape the structure and function of ecosystems as top-down effects on food webs can help maintain species diversity and resilience. This role is becoming more apparent as conservation efforts encourage the recovery and range expansion of many large carnivores. Many of the semi-aquatic pinnipeds are recovering well from past over-exploitation, particularly fur seals (Arctocephalus spp.). As populations return to pre-exploitation numbers and return to historical ranges, ecological theory predicts intra and interspecific competitive interactions will have a greater impact on ecosystem structure and function. The recovery of these populations provides an opportunity to explore the importance of competitive interactions, by investigating the behaviour of fur seals at the core of their ranges, where populations are at relatively high density and comparing them with those at the margins of their expanding ranges. The comparative approach can be further refined by separating fundamental limitations arising from morphological or reproductive constraints from ecological pressures by investigating the less well-known foraging behaviour of juveniles and males.

In this thesis I investigated inter-individual differences in foraging behaviour of three fur seal species, with a focus on adult males; Antarctic fur seals A. gazelle, Australian fur seals A. pusillus doriferus, and New Zealand fur seals A. forsteri. I tracked the foraging behaviour of individuals from large, established breeding colonies and haul-out sites with small populations at the joint range periphery of two species. Fur seals display a variety of foraging strategies (e.g. avoiding areas with high putative competition, focusing their search effort in areas of high biological production, partitioning niche space from congeneric species, high individual specialisation within benthic foraging species) that are consistent with foraging and niche theory, and that likely support intraspecific coexistence at large colonies and interspecific coexistence at range margins. Some important differences in foraging behaviour occur among individuals at a species range margin that distinguish them from individuals in the core of the species range. At this range periphery, the niche partitioning among males of sympatric fur seals offers insights into the processes driving foraging behaviour as species expand their range. Furthermore, an established network of protected areas could have useful management applications to mitigate negative interactions between humans and fur seals at their range periphery, and thereby support population expansion and recolonization of historical breeding areas. These insights provide direction for future research to support the conservation of fur seals and a more harmonious coexistence with humans.