Red List of South African Species

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Least Concern (LC)
Assessors: Claire Relton
Contributors: Doug Butterworth Ken Findlay Simon Elwen Michael Meÿer Herman Oosthuizen Stephanie Plön Matthew Child
Reviewers: Claire Relton

Rationale

The current IWC global estimate of abundance of Antarctic Minke Whales is about 500,000 individuals. The abundance estimates declined from about 700,000 for the second circumpolar set of abundance survey cruises (1985/86 to 1990/91) to about 500,000 for the third (1991/92 to 2003/04). Although this decline was not statistically significant, the IWC Scientific Committee does consider these results to reflect a change. However, whether this change is genuine or attributed to greater proportions of pack ice limiting the survey extent, has not yet been determined. More detailed results from an assessment model are available for the mid-Indian to the mid-Pacific region, and suggest that the population increased to a peak in 1970 and then declined, with it being unclear whether this decline has levelled off or is still continuing past 2000. There are no major identified threats within the assessment region. Hence, we retain the listing of Least Concern. If monitoring data and research verify a continuing genuine decline in the Antarctic, this species will need reassessment.

Regional population effects: The Antarctic Minke Whale exhibits seasonal migrations and is wide-ranging across the southern hemisphere. There are no barriers to dispersal, thus rescue effects are possible.

Distribution

The Antarctic Minke Whale is considered a southern hemisphere species, but is widely distributed from the equator to the ice edge.

During the summer, this species is abundantly distributed throughout the Antarctic waters, usually south of 60°S, and occurs in great concentrations near the ice edge but also to a limited extent within the pack ice and in stretches of open water surrounded by ice. High densities of Antarctic Minke Whales have been sighted in Prydz Bay, and in the Weddell and Ross Seas (Kasamatsu et al. 1997).

Their winter distributions are far more uncertain. There are sighting records of this species off Durban, South Africa, and historically, small numbers of individuals were caught in this region. In South African waters, their seasonal distribution has been described as bimodal, with peaks in April/May and again in September/October, which suggest that these individuals seasonally migrate northwards past the region in spring, and then southwards back to the southern oceans in autumn (Best 1982). At least some of the Antarctic Minke Whale population remains in the Antarctic in winter (Ensor 1989), but the proportion has not been quantified.

Population trend

Trend

Similar to other baleen whales, the IWC has divided the southern hemisphere longitudinally into six key geographical areas (pie slices, which range between 50° and 70° wide). Although biological evidence for these boundaries is generally weak, their delineation is useful in the description of baleen whale distribution and abundance. Antarctic Minke Whales are the most abundant of all Balaenopterid species in the southern hemisphere (Skinner and Chimimba 2005). Although the Dwarf Minke Whale is also present within Antarctic waters (as far south as approximately 65°S), they are far less common than the Antarctic Minke Whale, thus Minke Whale estimates of abundance taken south of 60°S, for simplicity’s sake, can be considered B. bonaerensis.

Ship-based summer abundance surveys have been conducted in the Antarctic, south of 60°S, since 1978/1979, covering different geographical areas each year (Matsuoka et al. 2001). It is assumed that the majority of the population occurs between 60°S and the pack ice zone during the survey season (Branch and Butterworth 2001, Shimada and Kato 2006). In 1990/1 a population estimate of 760,000 individuals was suggested (IWC 1991). However, subsequent surveys revealed lower population estimates (IWC 2001), and the new current estimate (2003/4) by the IWC is between 460,000 and 690,000 individuals. The most likely explanations include a decline in sighting efficiency, variations in the extent of pack ice or a combination of both. Another hypothesis, using multi-species modelling, is that they increased in abundance until the mid-20th century in response to increased krill abundance following the decline in other large baleen species (Mori and Butterworth 2006); and subsequently declined as other baleen species became protected and increased in number (thus competing for krill). Recently, catch data from 1990/1 to 2009/10 from the Japanese Whale Research Programme in the Antarctic revealed a 31% decrease in the weight of Antarctic Minke Whale stomach contents (Konishi et al. 2013), which support the hypothesis that the availability of krill has declined over the past 20 years. This possible decline is specific to minke whales, and is not reflected in abundance records for other Antarctic baleen species. Highest densities have been observed near the pack ice (Shimada and Kato 2006). Currently, no abundance estimates are available for Antarctic Minke Whales migrating through the assessment region.

The generation time estimated for Antarctic Minke Whales is 22 years (Taylor et al. 2007).

Threats

Commercial whaling of this species commenced in the 1970s, and ceased in 1986, when a whaling moratorium was enforced. However compared to other baleen whale species, Minke Whales were far less heavily exploited (Mori and Butterworth 2006) and commercial whaling began much later than it did for other species. Large-scale catches of this species only commenced in 1971, following the depletion of other larger baleen species (IWC 2006); before this, only small-scale experimental catches were conducted.

Approximately 100,000 Minke Whales are reported to have been caught during pelagic whaling expeditions in the Antarctic, and more than 14,000 from Costinha, the Brazilian land station, between 1964 and 1985. After 1987, whaling of this species continued to a lesser extent under a scientific permit, with records of 853 whales caught during the 2005/2006 season (Miyashita and Kato 2006). The current Japanese Scientific permit catch limit is set at 330 individuals.

Additionally, minor threats to Antarctic Minke Whales include bycatch in fishing gear (see van Waerebeek and Reyes 1994), and the effects of anthropogenic climate change. Increased sea temperatures in the Antarctic (Turner et al. 2006), resulting in a substantial loss of sea ice, may result in a substantial decline in food resources available to Southern Ocean baleen whales.

This species is relatively rare within South African waters and no major threats have been identified within South Africa’s EEZ (Exclusive Economic Zone).

Uses and trade

Major commercial whaling of Antarctic Minke Whales ceased in 1986, but currently under a scientific research permit issued by the Government of Japan, this species is hunted at a reduced level in the Antarctic.

Conservation

Large-scale commercial whaling of Antarctic Minke Whales effectively ceased in 1986 with the implementation of the IWC moratorium on commercial whaling. The summer range of this species also receives protection from the 1994 IWC Southern Ocean Sanctuary, which forbids whaling activity south of about 40°S. However, this does not prevent whales from being caught under a scientific permit.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) listed Antarctic Minke Whales on Appendix I, but this does not relate to Japan, who have registered an objection to this listing since July 2000. Additionally, Japan holds a reservation on the Southern Ocean Sanctuary. This species is also listed on Appendix II of the Convention on Migratory Species (CMS).

Although a local systematic monitoring programme would be beneficial for this species, this is not considered a priority, as Antarctic Minke Whales are under no major threat within South African waters. Additionally, no specific conservation interventions have been identified for this species in the assessment region.

Recommendations for managers and practitioners:
  • Systematic monitoring: design and implement a monitoring programme (acoustic and sightings) that can distinguish between Minke whale species in the southern hemisphere, in order to estimate population size and trends.
  • Ensure that accidental catches (in fishing or shark nets), strandings or collisions of Antarctic Minke Whales are reported, and managed by the relevant authorities, and in the case of mortality, make certain that the remains are made available for ongoing scientific investigation of the life history and genetics of this species.
Research priorities:
  • Research into the possible reasons behind the detected declining population trend.
  • Current population size, distribution and trend estimates.
  • Current and future threats which may impact this species, its habitat, or its primary food source.
  • Research into the use, trade, livelihoods and harvest trends associated with this species.
Encouraged citizen actions:
  • Save electricity and fuel to mitigate CO2 emissions and hence the rate of climate change.
  • Report any stranding reports to the relevant local authorities.

References 

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