Estimating the Average Age of First Birth in Marine Mammals

Abstract

The average age of sexual maturity and the average age of first birth should not be estimated with identical models. The two parameters often differ by at least 1 y because, among marine mammals, ovulation and parturition take place in different years because of the relatively long gestation period. Furthermore, the assumptions necessary to estimate the average age of sexual maturity cannot be made to fit the data used to estimate the age of first birth. Equating the two models is essentially equivalent to assuming that each ovulation will result in a birth. The described procedure lends itself well to age-specific data. Comparisons between populations should be with a Chi-square goodness-of-fit test.Key words: reproduction, marine mammals, sexual maturity