DISTRIBUTION, ABUNDANCE AND BREEDING CYCLE OF THE AUSTRALIAN SEA LIONNEOPHOCA-CINEREA (MAMMALIA, PINNIPEDIA)

Surveys of the Australian sea lion Neophoca cinerea were conducted thr oughout its range in Western and South Australia between December 1987 and February 1992. Almost every island was visited between Houtman Ab rolhos and The Pages (n = 255), many of them more than once. Sea lions breed on at least 50 islands, 27 in Western Australia and 23 in South Australia. Of the 50 breeding sites, 31 have not been reported previo usly. A further 19 islands may also support breeding colonies. A total of 1,941 pups was counted and pup production was estimated at 2,432. Only five colonies produced more than 100 pups each and they accounted for almost half of the pup production. Most of these colonies are nea r Kangaroo Island, South Australia. A breeding cycle of 17-18 months h as been reported for N. cinerea at Kangaroo Island and on the west coa st of Western Australia; this was also noted at another 11 islands whe re repeated visits coincided with breeding. No evidence was found for breeding seasons shorter or longer than 17-18 months. The breeding sea son was not synchronized between islands, as it is in other pinnipeds. A predictive model is developed to estimate the population size from pup production figures. It indicates that pup numbers should be multip lied by between 3.81 and 4.81 to estimate the total population size ju st before the pupping season begins. This leads to estimates of 9,300- 11,700 for the total population, considerably greater than earlier es timates. Causes of the unique reproductive cycle of N. cinerea art unk nown, but we hypothesize that it results from living in a temperate cl imate in some of the most biologically depauperate waters of the world . It is also clear that day length and water temperature cannot act as exogenous cues for implantation of the blastocyst; the physiological events of gestation must, rather, be cued endogenously.