A COMMENT ON THE AGE AT ONSET OF BREEDING OF MALE WEDDELL SEALS (LEPTONYCHOTES WEDDELLII)

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 (Lept onychotes 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. I n addition to methodological problems with the regression model used b y 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 mal e Weddell seals cannot be determined from that analysis.