Plotz, Roan ORCID: 0000-0001-7192-9931 (2003) Growth and Fasting Strategies of New Zealand Fur Seal, Arctocephalus forsteri, Pups at Cape Gantheaume, Kangaroo Island. Other Degree thesis, La Trobe University, Victoria.

Abstract

New Zealand fur seals (Arctocephalus forsteri) show pronounced inter-sexual differences in adult body size, and males will potentially mate with many females. Consequently, selection is thought to act differently upon pups during growth. Little is known about how male and female fur seal pups conserve energy, and use milk for growth especially as they fast for significant periods. There has been a plethora of studies that have viewed pinnipeds as ideal models for the differential investment theory, but the evidence remains equivocal. This study investigated a species that has shown some support for differential investment in the past, in the form of pup growth and maternal attendance behaviour, and looked at the potential that these intersexual differences are due to differential utilisation of maternal resources (different body compositions) and/or differential fasting strategies by pups, which may be determined by fasting mass loss rates. This study hopes to encompass both aspects of differential investment, such as maternal attendance, as well as differential fasting strategies of pups by looking at their fasting mass loss rates. This study found that males were larger and longer throughout the lactation period, yet grew at the same rate as females. There was no detectable intersexual difference in the maternal provisioning provided by mothers, in the form of attendance. There was some evidence that males and females have different fasting strategies, in that females, from a subset of pups exhibited significantly higher mass specific mass loss rates. This finding should be treated with caution however, as sample size was low, and cross sectional samples revealed no significant differences. Furthermore, study of the activity rates of the same pups over the duration of the fast, found no significant intersexual differences in activity rates. These results suggest that further studies are needed that encompass both aspects of differential investment theory, as well as differential utilisation by pups.

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