Growth and reproduction in the Icelandic grey seal

Abstract

Growth and reproduction in grey seals (Halichoerus grypus Fabricius, 1791) from Iceland were examined. The oldest Icelandic grey seals obtained were a 36 year old female and a 23 year old male. The longest animals were a 255 cm 13 year old male, and a 230 cm 20 year old female. The heaviest grey seal was an 11 year old male weighing 310 kg. The heaviest female was a 20 year old female that weighed 240 kg. Females reached an asymptotic standard length and weight of 200 (95% CI 196 - 204) cm and 164 (95% CI 157 - 171) kg. Males attained an asymptotic standard length of 243 (95% CI 232 - 254) cm and mass of 279 (95% CI 254 - 306) kg. Investigations of the ovaries and testes indicate that, by the time that females were seven years old, over 90% were pregnant. The average age of sexual maturity of females was 4.0 years (95% CI 3.59 - 4.41) and the average age of first pupping was 5.3 (95% CI 4.95 - 5.72). Average age of sexual maturity for males was 4.9 (95% CI 4.43 - 5.40). Seven out of 8 grey seal males had fully developed testes at the age of 7. All males, 8 years of age and older were mature. Adult (5+ years) females and males are fattest in the summer right before breeding in the autumn, but leanest in the winter after breeding and mating, and in the spring after moulting.