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Breeding biology of the Australian sea lion Neophoca cinerea

Gales, Nicholas John (1995) Breeding biology of the Australian sea lion Neophoca cinerea. PhD thesis, Murdoch University.

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Abstract

The breeding biology of the Australian sea lion was investigated throughout its geographic range between December 1987 and February 1992. Sea lions breed on at least 51 islands, 28 in Western Australia and 23 in South Australia. Thirty one of these islands had not been previously reported as sea lion breeding sites. A predictive model is developed to estimate the population size from pup production estimates from these locations. It indicates that pup numbers should be multiplied by between 3.81 and 4.81 to estimate the total population size just before the pupping season begins. Pup production was estimated at 2,432 which led to a total population estimate of 9,300-11,700, considerably greater than earlier estimates. Approximately half of the pup production occurs on five colonies near Kangaroo Island, South Australia. An unusual breeding cycle of 17-18 months has been reported for N. cinerea at Kangaroo Island; this study reports for the first time this unusual breeding cycle on islands throughout this species’ range. No evidence was found for breeding seasons shorter or longer than 17-18 months. The breeding season is not synchronised between islands, as it is in other pinnipeds, and the timing of breeding appeared random between sites.

Investigations of the reproductive physiology of this species conducted on Kangaroo Island, South Australia, revealed a 4-5 month embryonic diapause and an 11-12 month placental gestation. This unusually long placental gestation was not associated with the production of a precocious pup, but rather, I hypothesise in this study that foetal growth rate is retarded. Because of the non-seasonal, asynchronous reproductive cycle of N. cinerea the present results indicate that cues for the physiological events of gestation must be endogenous, rather than the exogenous cues hypothesised for other pinnipeds. Throughout the lactation that accompanies gestation, N. cinerea produces milk that is lower in fat (energy) than all but the tropical otariids (30.82 +/- 9.84% SD).

Analysis of scats and stomach contents indicate that N. cinerea has a broad diet and feeds on primarily benthic species. Such a diet is well suited to the low energy marine environment exploited by this species, in which there are few, if any, seasonal changes in food availability. Feeding trials indicated that analysis of scats alone is a poor methodology for quantifying diet.

In this study I hypothesise that the unique reproductive cycle and physiology of N. cinerea results from living in a stable climate in some of the most biologically poor waters of the world.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Williamson, Peter and Shaughnessy, Peter
URI: http://researchrepository.murdoch.edu.au/id/eprint/53087
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