Red List of South African Species

Alternatively, Explore species
| National Red List categories | Partners |
Critically Endangered (CR)
Assessors: Ken Findlay
Contributors: Simon Elwen Michael Meÿer Herman Oosthuizen Stephanie Plön
Reviewers: Matthew Child

Rationale

There are two Blue Whale subspecies found within the assessment region: the Antarctic Blue Whale B. m. intermedia and the Pygmy Blue Whale B. m. brevicauda. While the former has a circumpolar distribution and passes through South African waters in winter, the latter is most abundant in the Indian Ocean with only a few records from Durban and the Prince Edward Islands. The majority of the over 17,000 Blue Whales caught off southern Africa were probably Antarctic Blue Whales. The pre-whaling population of B. m. intermedia is estimated at 239,000 and was reduced to 360 individuals in 1973. Although the population has been estimated to be increasing since then, at a mean rate of 7.3% per annum, the current population size is estimated at below 5,000 mature individuals. The current population is thus still less than 3% of its level of three generations ago (at least a 95% decline) (1922–2015), and therefore qualifies for Critically Endangered A1abd based on records of past whaling catches and subsequent estimated population sizes. The population is currently increasing but at a slow rate relative to other whales that have become protected in the same period. Blue Whales exist in localised subpopulations and have call frequency rates at 19–28 Hz, which is the same as seismic surveys. Thus, although there are no major threats, increasing marine noise pollution through seismic surveys may interrupt or affect population recovery within the assessment region. Internationally, the area south of South Africa is an important stronghold for this species. Continued monitoring of population recovery and mitigation of potential noise pollution are recommended.

Regional population effects: Blue Whales are highly migratory and wide-ranging. There are no barriers to dispersal, so rescue effects are possible.

Distribution

Antarctic Blue Whales have a continuous circumpolar distribution and dominated (99.2%) pelagic catches south of 52°S, whereas Pygmy Blue Whales dominated (99.9%) north of 52°S (Branch et al. 2007b). During the austral summer feeding season, the Antarctic Blue Whale is found in polar waters and the Pygmy Blue Whale in temperate waters (Attard et al. 2012). Thus, the ranges of the two subspecies do not overlap in summer but they may overlap in winter if the Antarctic Blue Whale migrates into Pygmy Blue Whale habitat. Overall, the available evidence suggests that Antarctic Blue Whales generally do migrate to northerly locations in winter, although some overwinter in the Antarctic (Branch et al. 2007a). For example, analyses of length frequencies have reinforced the conclusion that Antarctic Blue Whales migrate to South African and Namibian waters in winter (Best 2007, Branch et al. 2007b). Additionally, acoustic data reveal that Antarctic Blue Whales use both the Indian and eastern Pacific Oceans concurrently, indicating that there is not a single migratory destination (Stafford et al. 2004). 

Antarctic Blue Whales have been recorded along bands stretching across entire ocean basins but at lower latitudes they are progressively more clustered, localized and compressed along the continental margins (Branch et al. 2007a), which probably reflects the distribution of krill, with large Antarctic Krill Euphausia superba at the highest latitudes, mid-sized Euphausia species in the mid latitudes and smaller Nyctiphanes species in coastal upwelling systems in the mid and low latitudes. Current sightings are aggregated close to the edge of the pack ice, while past catches extended further north, which may be explained by considering that, when Antarctic Blue Whales were more abundant, they occupied a wider habitat range, but now they are depleted to < 5% of their original abundance and concentrate close to the ice edge where krill is most prevalent (Branch et al. 2007a).

Antarctic Blue Whales occur throughout South Africa’s Economic Exclusion Zone (EEZ) from ice-edge to tropical and sub-tropical waters, excluding nearshore waters. However, very little feeding or breeding is believed to occur. Most feeding occurs in high latitudes of the Antarctic, breeding probably occurring in sub-tropical waters. Instead, the regional waters are probably used mainly as migratory corridors. They are a wide-ranging and migratory species, especially while in high latitudes (Best 2007). For example, Sremba et al. (2012) documented a female that travelled at least 6,650 km or 131° longitude over four years

Population trend

Trend

The Antarctic Blue Whale was extremely abundant in the past. However, whaling from 1928 to 1972 depleted the population from 239,000 (95% CI 202,000–311,000) to 360 (95% CI 150–840) in 1973 (Branch et al. 2004). Sightings remain rare in the Antarctic (0.17–0.52 / 1,000 km) despite considerable effort during dedicated sightings surveys. There are no published population estimates for the assessment region, but 72% of all Antarctic Blue Whale catches were made in the South Atlantic and western Indian Ocean areas, suggesting that the subregion included a significant portion of the entire population (Best 2007). Recorded sightings are also rare (only two since the 1960s) off south-west Africa where large catches were recorded from Saldanha Bay (South Africa) (n = 7,969), Namibia (n = 1,665) and Angola (n = 1,917) (Branch et al. 2007a). Similarly, 2,986 Blue Whales were caught off Durban and 417 from south-east South Africa from 1911 to 1916, which originally comprised Antarctic Blue Whales but by the end of the whaling period most catches and sightings were probably Pygmy Blue Whales (Branch et al. 2007b).

Monitoring subsequent population trends is difficult due to their current scarcity. However, Bayesian models fitted to three sighting series (1968–2001) indicated that the subspecies has been increasing at a mean rate of 7.3% per annum (1.4%–11.6%) (Branch et al. 2004). In 1996, population size was estimated at 1,700 individuals (95% CI 860–2,900), which constitutes 0.7% (0.3%–1.3%) of the pre-exploitation level (Branch et al. 2004). Similarly, the most recent abundance estimate in 1997 is 2,280 individuals (T. Branch unpubl. data), which is only 0.9% (CI 0.7–1.0%) of pre-exploitation levels. Currently, there are fewer than 5,000 mature individuals. Thus, although they have been increasing since illegal whaling ended in 1972, the rate is slow relative to other whales that have gone under protection in the same period and they still need to be protected as their current population size is still a fraction of the pre-exploitation era.

Models project that Blue Whales will continue to increase, while Minke Whales will decrease (following their historical increase due to over-harvesting of Blue Whales), as Blue Whales are better able to tolerate decreased krill abundance (Mori and Butterworth 2004). Generation length is estimated to be 31 years (Taylor et al. 2007).

Threats

Historical over-harvesting of Blue Whales reduced the population by 99% but ceased in 1972 and the population is currently recovering (Branch et al. 2004). There currently are no major direct anthropogenic threats. However, the small population sizes created by whaling makes Blue Whales susceptible to indirect threats, such as demographic stochasticity, inbreeding depression and density dispensation (Allee effects). Recently, Attard et al. (2012) found evidence for hybridisation between B. m. intermedia and B. m. brevicauda in Antarctica, which may be caused by an increase in the proportion of B. m. brevicauda off Antarctica in recent decades due to past whaling or current patterns of climate change. Despite the bottleneck imposed by whaling, the genetic diversity of B. m. intermedia remains relatively high (Sremba et al. 2012).

Within the assessment region, an emerging threat is marine noise pollution, especially through seismic surveys (Koper and Plön 2012). Frequency range of calls is between 19 and 28 Hertz, which overlaps with major frequencies of seismic surveys, which could mask calls of Blue Whales and disrupt social structure and breeding.

Climate change may become a threat in the future by altering sheet ice habitats and affect the food supply of this species. A profound reduction in the extent of sea ice in the Antarctic is expected, and possibly a complete disappearance in summer, as mean Antarctic temperatures rise faster than the global average (Turner et al. 2006). The implications of this for Blue Whales are unclear but warrant monitoring.

Uses and trade

Blue Whales were exploited on an industrial scale from 1905 to 1973 using deck-mounted harpoon cannons. Harvesting Blue Whales began in South Georgia and spread to Antarctica with the advent of factory-ships in the 1920s, 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 but illegal catches from the former USSR continued until 1972, which were primarily Pygmy Blue Whales.

Conservation

Blue Whales are protected worldwide, including in the Antarctic, by the International Whaling Commission, and no hunting currently occurs. Catch limits for all commercial whaling have been set at zero since 1986. The species is on Appendix I of both the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Convention on Migratory Species (CMS). Within the assessment region, they are also fully protected within the EEZ and Prince Edward Islands. The cessation of harvesting has allowed the population to recover (Branch et al. 2004), and it is recommended that ship-based surveys be conducted in South African waters to assist in determining the population size, distribution and seasonality for this species.

Additionally, careful management, regulation and enforcement of seismic survey practices will also benefit this species. Current mitigation measures include geographic and temporal restrictions (activity restricted to specific areas or times of year), source-based mitigation (sound containment and improvement or replacement of current equipment used), and operational mitigation (to follow a protocol of operation), which will help to simultaneously conserve South Africa’s coastal biodiversity and allow industrial developments (Koper and Plön 2012).

Recommendations for managers and practitioners:
  • Systematic monitoring: design and implement a monitoring programme (acoustic and sightings) that can detect population size and trends.
  • Develop best practice guidelines for seismic surveys and enforce regulations.
Research priorities:
  • Winter survey off Namibia might reveal a breeding ground (Best 1998).
  • Continued genetic research to resolve subspecies taxonomy and population structure, which is needed to design an effective monitoring programme.
Encouraged citizen actions:
  •  Reduce boat speed in bays and harbours.
  • When participating in whale/dolphin watching tours, ensure regulations are followed.

References 

[@book{275,
 address = {Cambridge},
 author = {Skinner, J.D. and Chimimba, C.T.},
 publisher = {Cambridge University Press, United Kingdom},
 title = {The Mammals of the Southern African Subregion},
 year = {2005}
}
,@article{2474,
 author = {Moore SE.},
 journal = {Journal of Mammalogy},
 pages = {534--540},
 title = {Marine mammals as ecosystem sentinels},
 volume = {89},
 year = {2008}
}
,@electronic{2474,
 address = {www.marinemammalscience.org},
 author = {Committee on Taxonomy},
 publisher = {Society for Marine Mammalogy},
 title = {List of marine mammal species and subspecies},
 year = {2017}
}
,@techreport{2476,
 author = {Kato, H., Honno, Y., Yoshida, H., Kojima, E., Nomura, A. and Okamura, H.},
 institution = {International Whaling Commission Scientific Committee},
 title = {Further developments on morphological and behavioral key for sub-species discrimination of southern blue whales, analyses from data through 1995/96 to 2001/02 SOWER cruises},
 year = {2002}
}
,@book{2476,
 address = {Cape Town, South Africa},
 author = {Best, P.B.},
 publisher = {Cambridge University Press},
 title = {Whales and Dolphins of the Southern African Subregion},
 year = {2007}
}
,@techreport{2476,
 author = {Koper RP, Plön S},
 institution = {Endangered Wildlife Trust, South Africa},
 title = {The potential impacts of anthropogenic noise on marine animals and recommendations for research in South Africa},
 year = {2012}
}
,@article{2477,
 author = {Branch, T., 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.B., Borsa, P., Brownell Jr., R.L., 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., Rankin, S., Samaran, F., Thiele, D., Van Waerebeek, K. and Warneke, R.M},
 journal = {Mammal Review},
 pages = {117--175},
 title = {Past and present distribution, densities and movements of blue whales <i>Balaenoptera musculus</i> in the Southern Hemisphere and northern Indian Ocean},
 volume = {37},
 year = {2007}
}
,@article{2477,
 author = {Turner, J., Lachlan-Cope, T. A., Colwell, S., Marshall, G. J. and Connolley, M.},
 journal = {Science},
 number = {5769},
 pages = {1914--1917},
 title = {Significant warming of the Antarctic winter troposphere},
 volume = {311},
 year = {2006}
}
,@article{2477,
 author = {Best, P.B., Rademeyer, R.A., Burton, C., Ljungblad, D., Sekiguchi, K., Shimada, H., Thiele, D., Reeb, D. and Butterworth, D.S.},
 journal = {Journal of Cetacean Research and Management},
 number = {3},
 pages = {253--260},
 title = {The abundance of blue whales on the Madagascar Plateau, December 1996},
 volume = {5},
 year = {2003}
}
,@article{2477,
 author = {Branch, T. A., Matsuoka, K. and Miyashita, T.},
 journal = {Marine Mammal Science},
 number = {4},
 pages = {726--754},
 title = {Evidence for increases in Antarctic blue whales based on Bayesian modelling},
 volume = {20},
 year = {2004}
}
,@article{2477,
 author = {Clapham, P. J., Aguilar, A. and Hatch, L. T.},
 journal = {Marine Mammal Science},
 pages = {183--201},
 title = {Determining spatial and temporal scales for the management of cetaceans: lessons from whaling},
 volume = {24},
 year = {2008}
}
,@article{2477,
 author = {Attard, C.R.M., Beheregaray, L.B., Jenner, K.C.S., Gill, P.C., Jenner, M.-N., Morrice, M.G., Robertson, K.M., and Moller, L.M. },
 journal = {Molecular Ecology },
 pages = {5715--5727},
 title = {Hybridization of Southern Hemisphere blue whale subspecies and a sympatric area off Antarctica: impacts of whaling or climate change?},
 volume = {21},
 year = {2012}
}
,@electronic{2477,
 address = {www.iucnredlist.org},
 author = {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. and Zerbini, A. N.},
 title = {<i>Balaenoptera musculus</i>. In 'The IUCN Red List of Threatened Species'. Version 2008},
 year = {2008}
}
,@article{2477,
 author = {Sremba, A. L., Hancock-Hanser, B., Branch, T. A., LeDuc, R. L., and Baker, C. S.},
 journal = {PLoS ONE},
 pages = {e32579},
 title = {Circumpolar diversity and geographic differentiation of mtDNA in the critically endangered Antarctic blue whale (<i>Balaenoptera musculus intermedia</i>)},
 volume = {7},
 year = {2012}
}
,@article{2477,
 author = {Stafford K.M.,  Bohnenstiehl D.R., Tolstoy M., Chapp E., Mellinger D.K. and Moore S.E.},
 journal = {Deep-Sea Research I},
 pages = {1337–1346},
 title = {Antarctic-type blue whale calls recorded at low latitudes in theIndian and eastern Pacific Oceans},
 volume = {51},
 year = {2004}
}
,@article{2477,
 author = {Branch, T. A., Abubaker, E. M. N., Mkango, S. and Butterworth, D. S.},
 journal = {Marine Mammal Science},
 number = {4},
 pages = {803–833. doi:10.1111/j.1748--7692.2007.00137.x},
 title = {Separating southern blue whale subspecies based on length frequencies of sexually mature females},
 volume = {23},
 year = {2007}
}
,@electronic{2477,
 address = {http://www.iucnredlist.org},
 author = {IUCN (International Union for Conservation of Nature)},
 title = {<i>Balaenoptera musculus</i>},
 year = {2012}
}
,@article{2477,
 author = {Mori M, Butterworth DS.},
 journal = {African Journal of Marine Science},
 pages = {245–259},
 title = {Consideration of multispecies interactions in the Antarctic: a preliminary model of the minke whale – blue whale – krill interaction.},
 volume = {26},
 year = {2004}
}
,@techreport{41713,
 author = {Taylor, B.L., Chivers, S.J., Larese, J. and Perrin, W.},
 institution = {Southwest Fisheries Science Center},
 title = {Generation Length and Percent Mature Estimates for IUCN Assessments of Cetaceans},
 year = {2007}
}
,@techreport{41713,
 author = {Best, P.B.},
 title = {Blue whales off Namibia – a possible wintering ground for the Antarctic population.},
 year = {1998}
}
,@techreport{41713,
 author = {Kato, H., Honno, Y., Yoshida, H., Kojima, E., Nomura, A. and Okamura, H.},
 title = {Further developments on morphological and behavioural key for sub-species discrimination of southern blue whales},
 year = {2002}
}
,@article{41713,
 author = {LeDuc, R.G., Dizon, A.E., Goto, M., Pastene, L.A., Kato, H., Nishiwaki, S., LeDuc, C.A. and Brownell Jr., R.L.},
 journal = {Journal of Cetacean Management and Research},
 pages = {73--80},
 title = {Patterns of genetic variation in Southern Hemisphere blue whales and the use of assignment test to detect mixing on the feeding grounds},
 volume = {9},
 year = {2007}
}
,@article{41713,
 author = {McDonald, M.A., Mesnick, S.L. and Hildebrand, J.A},
 journal = {Journal of Cetacean Research and Management},
 pages = {55--65},
 title = {Biogeographic characterisation of blue whale song worldwide:  using song to identify populations},
 volume = {8},
 year = {2006}
}
,]
Send feedback about this assessment to SANBI

Lead agencies, Partners and Funders

See the partners page