Age of puberty, life cycle length, and reproductive investment in female fur seals

Purpose: assessment of age at puberty, life cycle length, and reproductive contribution in female fur seals  over the life cycle.

Method: analysis of materials on the return of tags from fur seals from the generations of 1979–1997, obtained during the harem period at the Central site of the Northern rookery (Bering Island) in 1982–2014.

Novelty: For the first time, the life cycles of female fur seals from the generations of 1979–1997 have been completely traced. Information is presented on the duration of the life cycle of female fur seals, the age of entry into reproduction, and the reproductive contribution of females during the life cycle. The individual variability of life cycle parameters in female fur seals is shown.

Results: The age of the first exit of females to the rookery ranged from 2 to 17 years. During the study period, females spent from 1 to 17 breeding seasons on the haulout. The duration of the life cycle is subject to significant individual variation: only less than 5% of the females spent more than 10 breeding seasons on the rookery, about a third of the females went to the rookery more than 6 times, about half — more than 4 times, and about a third of the females went to the rookery 2–3 times. Almost half (44.2%) of puppies are born during the 2nd — 3rd reproductive season, more than 95% of puppies are born during the 2nd — 9th reproductive seasons, and only about 5% of female puppies are born during the 10th 17 reproductive seasons. At the age   of three, only 0.4% of puppies were born by females; at the age of 4–8 years — 57.6% of puppies; at the age  of 9–13 years — 30.8%; at the age of 14–19 years — 10.3% and at the age of 20–22 years — 0.9% of puppies. Skipping breeding seasons is an adaptation of females to high maternal costs for offspring.

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