Balaenoptera musculus ssp. intermedia
|Scientific Name:||Balaenoptera musculus ssp. intermedia|
|Species Authority:||Burmeister, 1871|
Balaenoptera musculus (Linnaeus, 1758)
The sub-specific taxonomy for Blue Whale is not yet fully elucidated in all regions, but the Antarctic Blue Whale is distinguished by its large body size and Antarctic distribution in summer. It is morphologically distinct from its neighbouring subspecies, the Pygmy Blue Whale (B. m. brevicauda (Ichihara 1966)), but only a limited number of the distinguishing characteristics are discernible at sea, making field differentiation between the two subspecies imperfect (Kato et al. 2002). The ranges of the two subspecies do not overlap in summer (Kato et al. 1995, Branch 2006) but they may overlap in winter if the Antarctic Blue Whale migrates into Pygmy Blue Whale habitat. The morphological distinction between Antarctic Blue Whales and those off western South America is not always clear (van Waerebeek et al. 1997, Palacios 1999) but the summer presence of the southeastern Pacific whales and the gap in summer sightings of Blue Whales between 44°S in Chile and the Antarctic implies that the Antarctic whales are geographically well separated from the southeastern Pacific whales. LeDuc et al. (2007) found that Antarctic blue whales were genetically distinct at the population level from Pygmy Blue Whales and southeastern Pacific whales, but no definitive, diagnostic genetic marker for the Antarctic Blue Whale has been found to date. A recent acoustic study has shown that the sounds produced by Antarctic and Pygmy Blue Whales are distinct (Ljungblad et al. 1998). The unique songs produced by both forms are also different from those produced by other blue whales world-wide (McDonald et al. 2006).
|Red List Category & Criteria:||Critically Endangered A1abd ver 3.1|
|Assessor(s):||Reilly, S.B., Bannister, J.L., Best, P.B., Brown, M., Brownell Jr., R.L., Butterworth, D.S., Clapham, P.J., Cooke, J., Donovan, G.P., Urbán, J. & Zerbini, A.N.|
|Reviewer(s):||Taylor, B.L. & Notarbartolo di Sciara, G. (Cetacean Red List Authority)|
The population is less than 3% of its level of three generations ago (at least a 97% decline) (1914-2007), and therefore qualifies for Critically Endangered (CR) under the reduction criterion A1 based on a combination of direct recent observations, and inferred reductions from known past catches (subcriteria a, b, d).
|Previously published Red List assessments:|
|Range Description:||The Antarctic Blue Whale occurs in summer between the Antarctic Polar Front and into the pack ice zone, being most abundant near the ice edge (Branch et al. 2007). Modern sightings are aggregated close to the edge of the pack ice, while past catches extended further north. Whether this is due to retreat of the pack ice since the time of catching (de la Mare 1997), or because the distribution of the species has contracted following exploitation, is unclear. Over 40,000 blue whales were caught in the waters around South Georgia, but the species is rare there now (Moore et al. 1999).|
The winter distribution is poorly known, except that Antarctic Blue Whales occur in winter around southern Africa (including South Africa, Namibia, Angola, and Congo) where they were formerly caught in large numbers (IWC 2006, Best 1998). Elsewhere there are scattered records, but the sub-specific identity is often in doubt. The assumption has been that animals migrate to lower latitudes in winter, but a portion of the population may remain in Antarctic all the year round.
Native:Angola (Angola); Antarctica; Argentina; Australia; Chile; Congo; Falkland Islands (Malvinas); French Southern Territories; Indonesia; Namibia; South Africa; South Georgia and the South Sandwich Islands (South Georgia, South Sandwich Is.)
|FAO Marine Fishing Areas:|
Atlantic – Antarctic; Indian Ocean – Antarctic; Pacific – Antarctic
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The Antarctic Blue Whale was extremely abundant in the past; about 341,830 blue whales were recorded caught in the Antarctic and sub-Antarctic (IWC 2006) in the 20th century, of which 12,618 were identified as pygmy blue whales or are assumed to have been so from their location (Branch et al. 2004). About 40,000 of these were taken around South Georgia. In addition, the majority of the over 17,000 blue whales caught off southern Africa were probably Antarctic Blue Whales (Branch et al. 2007). Ignoring these and other catches north of 40°S, Branch et al. (2004) estimated the pre-exploitation (1905) abundance to be 239,000 (202,000-311,000). The estimated population size in 1996, based primarily on data from the International Decade of Cetacean Research (IDCR)—later Southern Ocean Whale and Ecosystem Research (SOWER) programme—whale sightings cruises, was 1,700 (860-2,900) with an estimated annual rate of increase of 7.3% (1.4-11.6%). The default value of 31 years for generation time given in Taylor et al. (2007) was considered appropriate, given an absence of any indications to the contrary from available biological information for the species. That implies that the time window for applying the A (reduction) criterion is 1914-2007. Branch et al.'s initial (1905) population estimate can be taken as a conservative (i.e., negatively biased) proxy for the 1914 population size, because few (<1,000) catches were taken during 1904-11and those authors excluded the 17,000 catches off Southern Africa. Their estimate for the ratio of the 1996 population size to the initial is 0.7% (0.3-1.3%). Even allowing for a doubling of the population size since 1996, the Antarctic Blue Whale population remains below 3% of the 1914 level.|
|Current Population Trend:||Increasing|
|Habitat and Ecology:|
Antarctic Blue Whales are the largest living animal, with lengths up to 33.6 m. They feed almost exclusively on euphausiids (krill), especially Euphausia superba (Mackintosh and Wheeler 1929). In summer they feed predominantly near the edge of the pack ice zone.
|Movement patterns:||Full Migrant|
|Major Threat(s):||The main threat in the past was direct exploitation, which only became possible (on more than an occasional basis) in the modern era using deck-mounted harpoon cannons. Whaling on Antarctic Blue Whales began in 1904 based in South Georgia. With the advent of factory-ship whaling in the 1920s, catching spread around the Antarctic, reaching a peak in 1930-31 when more than 30,000 were taken. Southern Hemisphere Blue Whales have been protected under the International Whaling Convention since 1966. Continued illegal catches of blue whales by factory ships from the former USSR until 1972 were primarily Pygmy Blue Whales. The Antarctic Blue Whale population was reduced to a dangerously small size (low hundreds) by the end of whaling but is now increasing (Branch et al. 2004). Antarctic Blue Whales are not known to be subject to any current direct anthropogenic threats.|
Blue Whales are protected worldwide, including the Antarctic, by the International Whaling Commission, and no hunting currently occurs.
The species is on Appendix I of both CITES and CMS.
|Citation:||Reilly, S.B., Bannister, J.L., Best, P.B., Brown, M., Brownell Jr., R.L., Butterworth, D.S., Clapham, P.J., Cooke, J., Donovan, G.P., Urbán, J. & Zerbini, A.N. 2016. Balaenoptera musculus ssp. intermedia. The IUCN Red List of Threatened Species 2016: e.T41713A98837960.Downloaded on 01 October 2016.|
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