Variability of birth rates of fur seal females from different generations

Abstract

Purpose: аssessment of individual and long-term variability of birth rates in female fur seals and their impact on the population size. Method: analysis of materials of long-term reading of tags on female fur seals tagged with metal tags in 1964–1997. Novelty: for the first time, birth rates in females from the generations of 1964–1997 were calculated. throughout their entire life cycle. Results: birth rate during the life cycle in females from generations 1964–1997 was estimated, which varied from 0.5 to 3.3 pups per 1 female (including nulliparous females). Significant individual variability of birth rates was established: along with nulliparous females, there were females in generations who gave birth during their lifetime from 1 to 11 puppies. Analysis of the data showed that about a quarter of the females do not participate in reproduction; a third of females give birth to 1 puppy in the life cycle; about a third of the females give birth to 2–4 puppies. Only 8.6 % of females give birth to 5 puppies or more, however, these multiparous females give birth to more than a third of puppies (34.1 %) of the total number of puppies. The contribution to the reproduction of the population in females who gave birth to 1–3 puppies is approximately equal — they give birth to 18–20 % of puppies; it slightly decreases in females who have given birth to 4 puppies (14.5 %). Average population birth rates by years, calculated as the arithmetic mean of generations of females breeding in the corresponding years, significantly correlated with the total number of puppies born in these years (r = 0.64; p < 0.001).