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Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean

T.A. Branch 1, 2, * K.M. Stafford 3 D.M. Palacios 4, 5 C. Allison 6 J.L. Bannister 7 C.L.K. Burton 8 E. Cabrera 9 C.A. Carlson 10 B. Galletti Vernazzani 9 P.C. Gill 11 R. Hucke-Gaete 12 K.C.S. Jenner 13 M.N.M. Jenner 13 K. Matsuoka 14 Y.A. Mikhalev 15 T. Miyashita 16 M.G. Morrice 17 S. Nishiwaki 14 V.J. Sturrock 18 D. Tormosov 19 R.C. Anderson 20 A.N. Baker 21 P.B. Best 22 Philippe Borsa 23 R.L. Brownell, Jr 24 S. Childerhouse 25 K.P. Findlay 26 T. Gerrodette 24 A.D. Ilangakoon 27 M. Joergensen 28 B. Kahn 29 D.K. Ljungblad 30 B. Maughan 31 R.D. Mc Cauley 32 S. Mc Kay 17 T.F. Norris 33, 34 S. Rankin 24 Flore Samaran 35 D. Thiele 17 K. van Waerebeek 36 R.M. Warneke 37
Abstract : 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. 6. South-east Pacific blue whales have a discrete distribution and high sighting rates compared with the Antarctic. Further work is needed to clarify their subspecific status given their distinctive genetics, acoustics and length frequencies. 7. Antarctic blue whales numbered 1700 (95% Bayesian interval 860–2900) in 1996 (less than 1% of original levels), but are increasing at 7.3% per annum (95% Bayesian interval 1.4– 11.6%). The status of other populations in the Southern Hemisphere and northern Indian Ocean is unknown because few abundance estimates are available, but higher recent sighting rates suggest that they are less depleted than Antarctic blue whales.
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Submitted on : Wednesday, April 30, 2008 - 10:21:25 AM
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T.A. Branch, K.M. Stafford, D.M. Palacios, C. Allison, J.L. Bannister, et al.. Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean. Mammal Review, Wiley, 2007, 37, pp.116-175. ⟨10.1111/j.1365-2907.2007.00106.x⟩. ⟨hal-00276539⟩



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