Browsing by Subject "Antarctic blue whales"

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    Evidence for increases in Antarctic blue whales based on Bayesian modelling
    (Wiley, 2004) Branch, Trevor A; Matsuoka, Koji; Miyashita, Tomio
    Antarctic blue whales (Balaenoptera musculus intermedia) are the largest and formerly most abundant blue whale subspecies, but were hunted to near extinction last century. Estimated whaling mortality was unsustainable from 1928 to 1972 (except during 1942–1944), depleting them from 239,000 (95% interval 202,000–311,000) to a low of 360 (150–840) in 1973. Obtaining statistical evidence for subsequent increases has proved difficult due to their scarcity. We fitted Bayesian models to three sighting series (1968–2001), constraining maximum rates of increase to 12% per annum. These models indicated that Antarctic blue whales are increasing at a mean rate of 7.3% per annum (1.4%–11.6%). Informative priors based on blue whale biology (4.3%, SD = 1.9%) and a Bayesian hierarchical meta-analysis of increase rates in other blue whale populations (−3%, SD = 11.6%), suggest plausible increase rates are lower (although the latter has wide intervals), but a meta-analysis of other mysticetes obtains similar rates of increase (6.7%, SD = 4.0%). Possible biases affecting the input abundance estimates are discussed. Although Antarctic blue whales appear to have been increasing since Sovier illegal whaling ended in 1972, they still need to be protected-their estimated 1996 population size, 1,700 (860–2,900), was just 0.7% (0.3%–1.3%) of the pre-exploitation level.
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    Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean
    (Wiley, 2007) Branch, Trevor A; Stafford, K M; Palacios, D M; Allison, C; Bannister, J L; Burton, C L K; Cabrera, E; Carlson, C A; Galletti Vernazzani, B; Gill, P C; Hucke-Gaete, R; Jenner, K C S; Jenner, M N M; Matsuoka, K; Mikhalev, Y A; Miyashita, T; Morrice, M G; Nishiwaki, S; Sturrock, V J; Tormosov, D; Anderson, R C; Baker, A N; Best, P D; Borsa, P; Brownell Jr, R I; Childerhouse, S; Findlay, K P; Gerrodette, T; Ilangakoon, A D; Joergensen, M; Kahn, B; Ljungblad, D K; Maughan, B; Mccauley, R D; Mckay, S; Norris, T F; Oman Whale and Dolphin Research Group; Rankin, S; Samaran, F; Thiele, D; van Waerebeek, K; Warneke, R M
    1. Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303 239), sightings (4383 records of 8058 whales), strandings (103), Discovery marks (2191) and recoveries (95), and acoustic recordings. 2. Sighting surveys included 7 480 450 km of effort plus 14 676 days with unmeasured effort. Groups usually consisted of solitary whales (65.2%) or pairs (24.6%); larger feeding aggregations of unassociated individuals were only rarely observed. Sighting rates (groups per 1000 km from many platform types) varied by four orders of magnitude and were lowest in the waters of Brazil, South Africa, the eastern tropical Pacific, Antarctica and South Georgia; higher in the Subantarctic and Peru; and highest around Indonesia, Sri Lanka, Chile, southern Australia and south of Madagascar. 3. Blue whales avoid the oligotrophic central gyres of the Indian, Pacific and Atlantic Oceans, but are more common where phytoplankton densities are high, and where there are dynamic oceanographic processes like upwelling and frontal meandering. 4. Compared with historical catches, the Antarctic (‘true’) subspecies is exceedingly rare and usually concentrated closer to the summer pack ice. In summer they are found throughout the Antarctic; in winter they migrate to southern Africa (although recent sightings there are rare) and to other northerly locations (based on acoustics), although some overwinter in the Antarctic. 5. Pygmy blue whales are found around the Indian Ocean and from southern Australia to New Zealand. At least four groupings are evident: northern Indian Ocean, from Madagascar to the Subantarctic, Indonesia to western and southern Australia, and from New Zealand northwards to the equator. Sighting rates are typically much higher than for Antarctic blue whales.
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    Separating pygmy and Antarctic blue whales using ovarian corpora
    (2006) Branch, Trevor A
    Two Southern Hemisphere subspecies of blue whales exist: pygmy blue whales are shorter (≤ 79 ft, 24.2 m) and generally found north of 54°S in summer, while Antarctic (true) blue whales exceed 100 ft (30.5 m) and are found in more southerly waters. Abundance estimates of Antarctic blue whales rely on sightings south of 60°S but at-sea identification is difficult and these sightings may include some proportion of pygmy blue whales. Ovarian corpora (corpora lutea plus corpora albicantia) are permanent ovulation records that can be used to estimate this proportion. Pregnant females of the two subspecies may overlap at 72–79 ft (21.9–24.1 m), but pygmy blue whales at these lengths have high (> 4) corpora counts, contrasting with immature or newly mature Antarctic blue whales (0–3 corpora). Published papers yielded pairs of length-corpora data for 104 pygmy and 2,064 Antarctic region blue whales. The relationship between length and ovarian corpora counts is well fitted by logistic models (with negative binomial variability). A mixture model estimates that 0.4% (95% confidence interval 0.0–1.1%) of Antarctic region blue whales were pygmy blue whales, much lower than the “less than 7%” currently accepted by the IWC. If later ovarian corpora data (1947–51) are separately analysed, the estimated proportion is zero (95% CI = 0.0–0.5%), suggesting that the pygmy proportion in the Antarctic did not increase when Antarctic blue whales were greatly depleted. No support is found for Ichihara’s suggestion that high (>7) ovarian corpora counts in 78–81 ft Antarctic region catches were pygmy blue whales. These whales are instead explained by natural variability in Antarctic blue whales. These methods could be applied to blue whale males through the analysis of testes weight, and may hold promise in separating catches of other species with diminutive forms such as fin and minke whales.