The reproductive success of the Steller sea lion Eumetopias jubatus (Schreber, 1776) on Brat Chirpoev and Medny islands in 2001–2011

The reproductive success of the Steller sea lion was estimated based on monitoring the breeding performance of known-age branded females on Brat Chirpoev and Medny islands in 2001–2011. First pup birth occurred at 4 years of age, but the majority of females gave birth to their first pup at the age of 5 years on both islands. The period of the highest realization of female initial reproductive capacity on Medny Island was 4–5 years shorter compared to Brat Chirpoev Island. The differences were caused by a lower number of middle-aged females and a higher proportion of non-pregnant females on Medny Island. The low reproductive success of females is probably the main reason for the depression of the Steller sea lion population on Medny Island.