Regional differences in length at sexual maturity for female blue whales based on recovered Soviet whaling data

摘要

New blue whale ovarian corpora data from illegal Soviet catches in the Southern Hemisphere and northern Indian Ocean were recovered from the original logbooks. Catches north of 52pS were assumed to be pygmy blue whales (Balaenoptera musculus brevicauda, n= 1,272); those south of 56pS were assumed to be Antarctic (true) blue whales (B. m. intermedia, n= 153). Three probable Antarctic blue whales north of 52pS were excluded. Lengths at which 50% and 95% of females become sexually mature (L and L) were estimated from a Bayesian logistic model. These estimates are more precise than previous Japanese estimates because Soviet catches below the legal minimum of 70 ft (21.3 m) were 32 times greater. For pygmy blue whales L was 19.2 m (95% interval 19.1-19.3 m) and L was 20.5 m (95% interval 20.4-20.7 m). Antarctic L (23.4 m, 95% interval 22.9-23.9 m) was much longer than L for pygmy blue whale regions (18.4-19.9 m). The median L for the northern Indian Ocean was 0.5-0.6 m shorter than for pygmy blue whales from other regions; although statistically significant, these small length differences provide little support for northern Indian Ocean blue whales being a separate subspecies, B. m. indica.