A comment on the age at onset of breeding of male Weddell seals (Leptonychotes weddellii)

Abstract

In an otherwise valuable contribution, Bartsh et al. (S.S. Bartsh, S.D. Johnston, and D.B. Siniff. 1992. Can. J. Zool. 70: 680 – 692) reached the conclusion that the youngest age at which male Weddell seals (Leptonychotes weddellii) become sexually active in their breeding colonies was 7 years, with first breeding likely, on average, in year 8. While plausible, this conclusion was based on only 5 seals of known age and 9 seals whose age was estimated from a length – age regression model. In addition to methodological problems with the regression model used by Bartsh et al., its application to a sample of known-age male Weddell seals correctly predicted the ages of only 25% of seals in the range of ages likely to include the age at social maturity, and was commonly off by 3 – 5 years and more. The age at onset of sexual activity of male Weddell seals cannot be determined from that analysis.