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Revista Chilena de Historia Natural 81 (1): 137-149, 2008
Breeding season of the southern fur seal, Arctocephalus australis at Guafo Island,  southern Chile
The southern fur seal (Arctocephalus australis) has colonised an ample geographic coverage in South America. The population should present there reproductive synchronization and a strong latitudinal effect on its reproductive activities. This research intends to review those reproductive activities on Guafo island (43º33’ S, 74º51’ W, Chile) looking after the existence of synchronization and stability during successivebreeding seasons, considering birthing, mating and territorial seasonality. During both seasons we observed territorial males from the end of November to beginning of February, counting most of them during the 4th week in December. The period of synchronization for births was registered between the first and fourth week of December with a mean duration of 28.5 ± 2.1 days. The average maximum date for birthing on Guafo Island was estimated for the day 15, 5 of December. The period of mating synchronization was registered on a similar date to the birthing. However, the mean date of mating was estimated to be day 19 ± 1.4 during December with a synchronization period of 29 ± 4.2 days of duration. By using the average mating and birth dates we estimated the reproductive cycle in about 11 months 27 days for the species at Guafo. We only determined statistically significant differences for the date of maximum birth between seasons, not for mating neither for the seasonality of territories. We could determine stability for the population size and age cohorts but not for the poliginic index HPMT. Even when we obtained statistical differences for the birth dates, we could identify a marked seasonality and reproductive synchronization for the species (about 30 days). At the same time we could determine that the evaluated reproductive patterns presented a temporal stability in the region, a condition shared with the rest of the Otariids of temperate environments. By comparing results with those presented for other sites in South America we evidenced differences in about 30 days for the dates of birthing, mating and territory establishments. This information has to be actualized as soon as possible for understanding with actual filogeographic tools the ecological history and evolution of this species in the Neotropics.
Key words:
Arctocephalus australis, reproductive patterns, reproductive synchronization, polygyny

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