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Marine Ecology Progress Series

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MEPS 293:283-302 (2005)  -  doi:10.3354/meps293283

Dietary resource partitioning among sympatric New Zealand and Australian fur seals

Brad Page1,2,*, Jane McKenzie1, Simon D. Goldsworthy1,2

1Sea Mammal Ecology Group, Zoology Department, La Trobe University, Bundoora Campus, Victoria 3086, Australia
2Present address: South Australian Research and Development Institute (Aquatic Sciences), PO Box 120, Henley Beach, South Australia 5022, Australia

ABSTRACT: Adult male, female and juvenile New Zealand and Australian fur seals Arctocephalus forsteri and A. pusillus doriferus regularly return to colonies, creating the potential for intra- and inter-specific foraging competition in nearby waters. We hypothesise that the fur seals in this study utilise different prey, thereby reducing competition and facilitating coexistence. We analysed scats and regurgitates from adult male, female and juvenile New Zealand fur seals and adult male Australian fur seals and compared prey remains found in the samples. Most prey consumed by adult male and female fur seals occur over the continental shelf or shelf break, less than 200 km from Cape Gantheaume. Adult female fur seals utilised proportionally more low-energy prey such as large squid and medium-sized fish. The adult female diet reflected that of a generalist predator, dictated by prey abundance and their dependant pups’ fasting abilities. In contrast, adult male New Zealand and Australian fur seals consumed proportionally more energy-rich prey such as large fish or birds, most likely because they could more efficiently access and/or handle such prey. Juvenile fur seals primarily consumed small fish that occur in pelagic waters, south of the shelf break, suggesting juveniles cannot efficiently utilise prey where adult fur seals forage. The age and sex groups in this study employ dramatically different strategies to maximise their survival and reproductive success and consequently the prey that they utilise reflect their different physiological constraints and metabolic requirements.

KEY WORDS: Arctocephalus · Fur seal · Diet · Sexual dimorphism · Competition · Eudyptula minor · Foraging ecology

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