Browsing by Subject "Bayesian"

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    A Bayesian analysis of the squid resource Loligo reynaudii
    (2012) Glazer, Jean Patricia; Butterworth, Doug S
    A Bayesian assessment of the squid resource was last performed in 2010. This paper presents results from an updated Bayesian assessment given that additional years’ data are now available.
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    Regional 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 A
    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 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.
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    Separating southern blue whale subspecies based on length frequencies of sexually mature females
    (Wiley, 2007) Branch, Trevor A; Abubaker, E M N; Mkango, S; Butterworth, Doug S
    When sexually mature, Antarctic (true) blue whales are substantially longer than pygmy blue whales. To estimate the proportions of these two subspecies in various regions, Bayesian mixture models were fitted to catch length frequencies of sexually mature females. The extent of rounding to 5-ft intervals was also estimated. Antarctic blue whales dominated (99.2%) pelagic catches south of 52°S, whereas pygmy blue whales dominated (99.9%) north of 52°S and in 35°–180°E. South of 60°S, only 0.7% (95% credibility interval 0.5%–1.0%) were pygmy blue whales, lower than the 7% upper bound currently assumed. Shore-based catches from SW Africa and those before 1937 from South Georgia and the South Shetlands were estimated to contain 90%–92% Antarctic blue whales. Actual proportions were probably higher, but these data show evidence of rounding (up to 19% of records), poor length-estimation methods, and other problems. The mean length of sexually mature female Chilean blue whales (77.1 ft, 23.5 m) was intermediate between pygmy (68.9 ft, 21.0 m) and Antarctic blue whales (83.4–86.3 ft, 25.4–26.6 m). A good fit to these data was obtained only by assuming that the Chilean whales are a separate subspecies or distinctive population. This finding is also consistent with their discrete distribution, and genetic and call type differences, compared to Antarctic and pygmy blue whales.