Browsing by Subject "corpora lutea"
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- ItemRestrictedRegional differences in length at sexual maturity for female blue whales based on recovered Soviet whaling data(Society for Marine Mammalogy, 2008) Branch, Trevor A; Mikhalev, Y ANew 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 52°S were assumed to be pygmy blue whales (Balaenoptera musculus brevicauda, n= 1,272); those south of 56°S were assumed to be Antarctic (true) blue whales (B. m. intermedia, n= 153). Three probable Antarctic blue whales north of 52°S were excluded. Lengths at which 50% and 95% of females become sexually mature (L50 and L95) 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 L50 was 19.2 m (95% interval 19.1–19.3 m) and L95 was 20.5 m (95% interval 20.4–20.7 m). Antarctic L50 (23.4 m, 95% interval 22.9–23.9 m) was much longer than L50 for pygmy blue whale regions (18.4–19.9 m). The median L50 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.
- ItemRestrictedSeparating pygmy and Antarctic blue whales using long-forgotten ovarian data(Wiley, 2009) Branch, Trevor A; Mikhalev, Y A; Kato, HPygmy blue whales (Balaenoptera musculus brevicauda) are ≤24.1 m and are generally found north of 52°S in summer, whereas the more southerly Antarctic blue whales (B. m. intermedia) may exceed 30 m. Previous assessments have assumed that catches and recent surveys south of 60°S recorded Antarctic blue whales, but these may have included pygmy blue whales. Here, we use ovarian corpora, which accumulate with ovulations and hence with length, to separate these subspecies. The resulting Bayesian mixture model, applied to 1,380 Northern Region (north of 52°S and 35°–180°E) and 3,844 Southern Ocean (south of 52°S) blue whales, estimated that only 0.1% (95% credibility intervals 0.0%–0.4%) of the Antarctic region blue whales were pygmy blue whales and, unexpectedly, found significantly lower lifetime ovulation counts for pygmy blue whales than for Antarctic blue whales (7.6 vs. 13.6). Over four decades, despite substantial depletion of Antarctic blue whales, there was no trend in the estimated proportion of pygmy blue whales in the Antarctic. Several lines of investigation found no evidence for sizeable numbers of pygmy blue whales in ovarian corpora data collected in the 1930s, as was previously hypothesized.