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Balaenoptera bonaerensis 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Cetartiodactyla Balaenopteridae

Scientific Name: Balaenoptera bonaerensis Burmeister, 1867
Common Name(s):
English Antarctic Minke Whale
Spanish Ballena Minke Antártica
Taxonomic Notes: Until the 1990s, only one species of Minke Whale was recognized, the Antarctic Minke Whale Balaenoptera bonaerensis being regarded as conspecific with the Common Minke Whale (B. acutorostrata). Most of the scientific literature prior to the late 1990s uses the name B. acutorostrata for all Minke Whales including Antarctic Minke Whales. Since 2000, the International Whaling Commission (IWC) Scientific Committee has recognized Antarctic Minke Whales as the separate species B. bonaerensis, while all Northern Hemisphere Minke Whales and all Southern Hemisphere "dwarf" Minke Whales are regarded as B. acutorostrata (IWC 2001). This has been followed by management and treaty bodies, such as Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This is based on genetic and morphological evidence that the two Minke Whale species, which are partially sympatric in the Southern Hemisphere, are distinct species (Rice 1998, Wada et al. 1991, Pastene et al. 1994, Pastene et al. 2007).

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2018
Date Assessed: 2018-01-02
Assessor(s): Cooke, J.G., Zerbini, A.N. & Taylor, B.L.
Reviewer(s): Reeves, R., Jackson, J. & Brownell Jr., R.L.
Contributor(s): Stanfield, M.
Facilitator/Compiler(s): Lowry, L.
Justification:

The Antarctic Minke Whale was previously listed as Data Deficient pending clarification of abundance and trends (Reilly et al. 2008). The IWC Scientific Committee has since accepted circumpolar population estimates of about 500,000 based on surveys conducted during 1993-2004 (IWC 2013). The population was estimated to have declined by 31% relative to the previous circumpolar surveys (1986-1991) but imprecision in the abundance estimates means that the decline is not statistically significant. In addition, an unknown proportion of the population would have been in unsurveyed pack ice habitat at the time of the surveys (Williams et al. 2014). The imprecise abundance and unknown proportion of whales in pack ice contributes to an overall lack of confidence in status determination based on decline rate. Because the decline may not have ceased and its causes are not understood, Red List criterion A2b for Vulnerable, for which the decline threshold is 30%, could apply. Given an estimated generation time of 22 years (Taylor et al. 2007), the time window for application of the A2 criterion would be 1952-2018. In the absence of a decline estimate for the whole period, and lacking understanding of the cause of the suspected decline, the Antarctic Minke Whale is classified as Near Threatened (NT), approaching Criterion A2b, following the Red List Guidelines because the species represents a case where, considering all available evidence, Least Concern, NT, and Vulnerable are equally plausible.

Previously published Red List assessments:

Geographic Range [top]

Range Description:

The Antarctic Minke Whale is considered a Southern Hemisphere species, although there are records north of the equator from Suriname (de Boer 2015) and occasional vagrants as far as the Arctic (Glover et al. 2010).  In summer they are abundant throughout the Antarctic south of 60°S, occurring in greatest densities near the ice edge, and to some extent within the pack ice and in polynyas. Particularly high densities have been observed in some years in high Antarctic areas such as Prydz Bay, the Weddell Sea, and the Ross Sea (Kasamatsu et al. 1998). Although Common Minke Whales have been found in the Antarctic as far south as 65°S they are much less common there than Antarctic Minke Whales (Branch and Butterworth 2001), such that all “Minke Whale” abundance estimates south of 60°S can for practical purposes be treated as estimates of Antarctic Minke Whale abundance.

Although Minke Whales are seen outside the Antarctic in summer (Kasamatsu and Miyashita 1983) much of the summer data is ambiguous with respect to identification as Common or Antarctic Minke Whales, such that it remains unclear whether significant numbers of Antarctic Minke Whales occur outside the Antarctic in summer. 

The winter distribution is not well known. Some Minke Whales remain in the Antarctic in winter (Ensor 1989). Following the unambiguous association of the "bio-duck" call with Antarctic Minke Whales (Risch et al. 2014), it has become easier to detect their presence in winter, and it appears they remain abundant year-round in at least some areas, such as the western Antarctic Peninsula (Dominella and Širović 2016). There is a wintering area off Costinha, Brazil (7°S), where Minke Whales, almost exclusively Antarctic Minke Whales, were the target of a whaling operation during 1964-85, with the peak abundance in October (da Rocha and Braga 1982). Minke Whales were also seen (and small numbers caught) off Durban, South Africa: the seasonal distribution was bimodal, with peaks in April/May and September/October, suggestive of migration past the area (Best 1982). There are occasional records from Peru (VanWaerebeek and Reyes 1994).

Japanese scouting vessel data indicated high abundance of Minke Whales (species ambiguous) in November between 10°–30°S in the central South Pacific and in much of the eastern and southern Indian Ocean from the tropics southwards to 50°S (Miyashita et al. 1996). The limited information available from low-latitude surveys from the 1987/88 season onwards, when the two Minke Whale species were reliably distinguished, indicates that most were Antarctic Minke Whales, probably on route from (as yet unknown) low-latitude breeding grounds to the Antarctic (Kasamatsu et al. 1995). The lack of any known areas of high concentration in winter suggests that the breeding distribution is rather dispersed and largely offshore. The species identity of Minke Whales seen in Indonesian waters in November (Miyashita et al. 1996) is unclear.

Migratory connections between wintering and feeding grounds are poorly known. The recovery of two Minke Whales marked in the Antarctic in Area II at 62° and 69°S (Buckland and Duff 1989) by the whaling station in the Costinha demonstrates that at least some individuals from Brazil migrate to the Antarctic. In addition, one whale accidentally marked with a Discovery mark at 28°S, 154°W and recovered at 73°S, 167°W (Horwood 1990) and another instrumented with a satellite transmitter near the Antarctic Peninsula and tracked to ~15°S, 100°W (Gales et al. 2013) provide evidence of similar north-south movements in the Pacific.



Countries occurrence:
Native:
Antarctica; Argentina; Australia; Brazil; Chile; French Southern Territories; Namibia; New Zealand; Peru; South Africa; South Georgia and the South Sandwich Islands; Suriname; Uruguay
FAO Marine Fishing Areas:
Native:
Atlantic – southwest; Atlantic – southeast; Atlantic – western central; Indian Ocean – western; Indian Ocean – eastern; Indian Ocean – Antarctic; Pacific – southeast; Pacific – southwest; Pacific – Antarctic
Additional data:
Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:

As for other baleen whales, the IWC’s management of Antarctic Minke Whales has been based on six Areas, I through VI, which are longitudinal pie slices 50°–70° wide. The population structure is poorly known, but recent analyses suggest a genetic distinction between whales in the Indian Ocean sector of the Antarctic (west of 165°E) and the Pacific Ocean sector (east of this line) with presumably some overlap (Pastene and Goto 2016). With the exception of the two marked whales mentioned above, the relationship between the Antarctic distribution and putative breeding areas is largely unknown.

Ship-based summer surveys of the area south of 60°S were conducted each summer from 1978/79 to 2009/10, under the auspices of the IWC Scientific Committee, as part of the International Decade of Cetacean Research—later Southern Ocean Whale and Ecosystem Research—programme, and covering a different area each year, such that circumpolar coverage was achieved  every 6-10 years (IWC 2011). These have been used to estimate Minke Whale population sizes, on the assumption that the bulk of the population is found south of 60°S in the survey season (Branch and Butterworth 2001). The survey vessels do not enter the pack ice, where Minke Whales are known to occur to some extent (Williams et al. 2014). Since then surveys have continued under a Japanese national programme in the southwest Pacific and southeast Indian Ocean sectors (Hakamada et al. 2013).

The IWC Scientific Committee in 2012 agreed upon abundance estimates totalling 720,000 (95% confidence interval (CI) 512,000-1,012,000) for the period 1986-91 and 515,000 (95% CI 361,000-733,000) for the period 1993-2002, with a 31% decline between the means of the two periods. However, the confidence intervals of the two estimates overlap and the IWC report listed a number of factors that could affect the comparison (IWC 2013). The Committee did not feel able to produce reliable estimates from the 1979-85 data. The Committee noted substantial inter-annual variability in the estimates over and above what would be expected from sampling variance, which is suggestive of genuine fluctuations in distribution (IWC 2015). The Committee has to date been unable to identify a definite cause for the decline, but has considered population models that are capable of reproducing the decline given certain assumptions (IWC 2015). Some evidence suggests that the pre-whaling population of Antarctic Minke Whales was lower than recent abundance (Mori and Butterworth 2006), while other evidence points to pre-whaling populations similar to or greater than recent abundance (Ruegg et al. 2010).       

Current Population Trend:Unknown
Additional data:
Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:

While in the Antarctic, Minke Whales feed almost exclusively on euphausiids (krill), primarily Euphausia superba, but also E. crystallorophias, E. frigida, and Thysanoessa macrura (Tamura and Konishi 2009). Observed densities of Minke Whales are highest near the edge of the pack ice, but they also occur within the pack ice (Williams et al. 2014). It is not known whether Antarctic Minke Whales feed to any significant extent while outside the Antarctic on their wintering grounds or migration routes. Best (1982) found a very low level of feeding, almost entirely on euphausiids, by Antarctic Minke Whales taken in winter off Durban, South Africa. Antarctic Minke Whales may themselves be an important prey for type-A Killer Whales, Orcinus orca (Pitman and Ensor 2003).

The Antarctic Minke Whale is considered pagophilic (ice-loving) in the sense of being better able than the larger baleen whales to use habitat with high pack ice densities. The proportion of the population found within the pack ice is not well known but has been estimated at 10-50% in Area IV (southeast Indian Ocean sector) in summer (Kelly et al. 2014).

Antarctic Minke Whales reach sexual maturity at about 7-8 years of age and the generation time is estimated to be 22 years (Taylor et al. 2007).

Systems:Marine
Continuing decline in area, extent and/or quality of habitat:Unknown
Generation Length (years):22

Use and Trade [top]

Use and Trade:

Antarctic Minke Whales are hunted under special permits issued by the government of Japan for scientific purposes according to Article VIII of the International Convention for Regulation of Whaling. Products from whales taken under special permits are sold only on the Japanese domestic market. The only international trade (in the sense defined by CITES) involves Introduction from the Sea (CITES 2017).

Threats [top]

Major Threat(s):

Whaling of Antarctic Minke Whales has not been as intensive as for the larger baleen whales. Substantial catches, apart from some experimental catches in the late 1960s, have been made by pelagic expeditions only since 1971, following depletion of the larger baleen whales. Nearly 100,000 Minke Whales were taken by pelagic whaling expeditions in the Antarctic during 1972-87, in addition to over 14,000 taken from the Brazilian land station at Costinha during 1964–85 and over 1,100 off South Africa during 1968-75 (Allison 2017). Since 1987, pelagic whaling continued under special permit at a reduced level. Nearly 11,000 Minke Whales were taken under such permits during 1987-2014. Catches were suspended for the 2014/15 season following a ruling by the International Court of Justice but resumed from the 2015/16 season with an annual catch target of 333 whales (IWC 2017).  

Sea ice cover in the Antarctic is predicted to decline by 50% in winter and 30% in summer (Cavanagh et al. 2017) and there is concern that this could negatively impact species such as Antarctic Minke Whales for which areas with sea ice constitute a substantial part of their habitat.

Conservation Actions [top]

Conservation Actions:

Antarctic Minke Whales were subject to IWC catch limits soon after exploitation started. Catch limits for commercial whaling became zero from 1986 with the coming into effect of the IWC moratorium on commercial whaling. The summer range of Antarctic Minke Whales is also nominally protected by the IWC Southern Ocean Sanctuary, adopted in 1994, which prohibits catches south of a boundary located mainly at 40°S. Neither the moratorium nor the sanctuary provision applies to takes of whales under Special Permits issued by IWC member governments. Such catches continued from 1987 until 2014 when the International Court of Justice ordered a stop to the permit programme on the grounds that it was not for purposes of scientific research (Clapham 2015). Catches resumed from the 2015/16 season under a new programme (IWC 2017).

Antarctic Minke Whales are listed on Appendix I of the  Convention on International Trade in Endangered Species (CITES), but this does not apply to products landed in Japan because the party holds a reservation on this species under CITES. Japan also holds a reservation on the IWC Sanctuary provision and therefore is not bound by it. The species is listed in Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals.


Citation: Cooke, J.G., Zerbini, A.N. & Taylor, B.L. 2018. Balaenoptera bonaerensis. The IUCN Red List of Threatened Species 2018: e.T2480A50350661. . Downloaded on 19 July 2018.
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