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Balaenoptera acutorostrata

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA CETARTIODACTYLA BALAENOPTERIDAE

Scientific Name: Balaenoptera acutorostrata
Species Authority: Lacépède, 1804
Common Name(s):
English Common Minke Whale, Minke Whale, Lesser Rorqual, Little Piked Whale, Dwarf Minke Whale
French Baleinoptère à museau pointu, Petit rorqual
Spanish Ballena Minke, Rorcual Menor
Taxonomic Notes: Until the 1990s, only one species of minke whale was recognized, the Antarctic Minke Whale B. bonaerensis being regarded as conspecific with 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 (SC) has recognized Antarctic Minke Whales as the separate species B. bonaerensis, and provisionally assigns all northern hemisphere minke whales and all southern hemisphere "dwarf" minke whales to the single species B. acutorostrata (IWC 2001). This has been followed by management and treaty bodies, such as the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Convention on Migratory Species (CMS).

The Dwarf Minke whale is a form of B. acutorostrata in the southern hemisphere. It was described there by Best (1985) and Arnold et al. (1987) in terms of its differences from the Antarctic Minke Whale. Subsequent genetic analyses (Wada et al. 1991, Pastene et al. 1994) revealed that the Dwarf Minke whale is conspecific with the "ordinary" minke whale of the northern hemisphere, while the Antarctic Minke Whale is a separate species (see separate listing).

Rice (1998) suggests three subspecies: B. a. acutorostrata in the North Atlantic, B. a. scammoni (= B. a . davidsoni) in the North Pacific, and the Dwarf Minke Whale as an unnamed subspecies in the southern hemisphere. However, given the limited sampling of Dwarf Minke Whales to date, it may be premature to assume that southern hemisphere populations of B. acutorostrata are more closely related to each other than they are to either northern hemisphere population. For example, Pastene (2006) observed that Dwarf Minke Whales from Brazil shared mitochondrial (mt) DNA haplotypes with individuals from both the North Atlantic and Dwarf Minke Whales from the Antarctic. In addition, Dwarf Minke Whales from Chile were closely related to animals from Brazil (Acevedo et al. 2005).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
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)
Justification:
There is no estimate of total global population size, but estimates from parts of the range in the Northern Hemisphere (totalling in excess of 100,000 individuals) show that it is well above the thresholds for a threatened category. While declines have been detected or inferred in some areas, there is no indication that the global population has declined to an extent that would qualify for a threatened category.
History:
1994 Insufficiently Known (Groombridge 1994)

Geographic Range [top]

Range Description: The Common Minke Whale is a cosmopolitan species found in all oceans and in virtually all latitudes, from 65°S to 80°N. In parts of its range it is very abundant, in other parts much less so. Its migration patterns are poorly known. It occurs in the North Atlantic, the North Pacific, and the Southern Hemisphere, but is not known from the northern Indian Ocean.

North Atlantic
In summer, Minke Whales are common throughout the northern North Atlantic as far north as Baffin Bay, Greenland Sea, Svalbard (Norway), Franz Josef Land and Novaya Zemlya (Russian Federation), and as far south as 40°N (New Jersey) on the US east coast (Anon. 2005a), and as far south as the Hebrides (northwest British Isles) and the central North Sea in the east. In the mid-Atlantic summer concentrations of minke whales occur to at least as far south as 50°N (Sigurjónsson et al. 1991). It is likely that at least a part of the Minke Whale population over-winters in the summer range, but there has been very little observation effort in winter to confirm this.

Minke Whales also occur south of this range in the southeastern North Atlantic, but with no obvious seasonality, and are not common, with the exception of the Canary Islands, where they appear to be frequent year-round (Van Waerebeek et al. 1999). There have been occasional sightings (Aguilar et al. 1983) and strandings (Van Waerebeek et al. 1999) off Spain and Portugal, Western Sahara, Mauritania and Senegal. Minke whales are rare in the Azores and not recorded from Madeira. The minke whale is considered a “visitor species” in the Mediterranean (average <1 record per year) with one vagrant recorded in the Black Sea (Reeves and Notabartolo di Sciara 2006).

There are very few winter records, but a summary by Mitchell (1991) indicates that they do occur in winter near Bermuda, the Bahamas and the Antilles, and the US coast south of 40°N. Ten strandings have been recorded in the Gulf of Mexico (Jefferson and Schiro 1997) but hardly any live sightings. A Norwegian winter expedition sent to the tropical Atlantic in 1989/90 to “find the breeding grounds of the minke whale” encountered just two minke whales, at 20°N and 10°N off West Africa in December (Folklow and Blix 1991).

North Pacific
Minke whales occur in summer right across the North Pacific north of about 30°N in summer, with a tendency for the distribution to shift northward in high summer. They are particularly abundant in the Okhotsk Sea in August (Miyashita et al. 1995), and also occur in the Bering Sea, around the Aleutian Islands and in the Gulf of Alaska (Moore et al. 2002, Zerbini et al. 2006) and the Chukchi Sea (Ivashin and Votrogov 1981). In the eastern North Pacific, there appears to be a year-round population off California and Baja California and in the Gulf of California, and minke whales occur in summer off Oregon, Washington and British Columbia (Anon. 2003). They have been seen off Hawaii but are not common there (Anon. 2005b).

In the western North Pacific, there are at least two distinct subpopulations: the so-called “J stock,” an autumn-breeding population that occurs in the Yellow Sea, East China Sea and Sea of Japan, with some penetration into the Okhotsk Sea in summer; and the O-stock which, like most baleen whales, breeds in winter, and occurs in summer in the northwestern Pacific, including the northeastern coasts of Japan, and in the Okhotsk Sea (Omura and Sakiura 1956, Kato 1992).

The winter distribution is poorly known. Japanese expeditions to look for wintering grounds in the southwestern North Pacific during 1993-95 failed to locate any minke whales (Miyashita et al. 1996). The timing of the arrival of minke whales in Korean and western Japanese waters is suggestive of migration from the south in spring and return in autumn (Ohsumi 1983). The wintering area in the eastern North Pacific has been identified acoustically to be primarily between 15 and 35 degrees N latitude (Rankin and Barlow 2005).

Southern hemisphere
Much of the data on the occurrence of minke whales in the Southern Hemisphere is ambiguous with respect to identification as B. acutorostrata or B. bonaerensis, because the two species are partially sympatric. Japanese scouting vessel data indicated high abundance of minke whales in November between 10°-30°S in the central South Pacific and in much of the eastern and southern Indian Ocean down to 50°S (Miyashita et al. 1995), but their species identity is unclear. The limited information available from surveys in low and middle latitudes from the 1987/88 season onwards, when the two species were reliably distinguished, indicates that most of the minke whales are B. bonaerensis (Nishiwaki et al. 1991), probably on route to the Antarctic from (as yet unknown) low-latitude breeding grounds, but also that B. acutorostrata is present in these latitudes.

Dwarf minke whales occur at higher latitudes but are much less common than B. bonaerensis. Of more than 1,700 minke whales taken by Antarctic pelagic whaling from the 1987/88 to the 1992/93 season (when the two species have been reliably distinguished), only 16 were dwarf minke whales (Nishiwaki et al. 2005). One was taken at 65°S and the remainder at between 55-62°S, the northern limit of whaling operations.

In coastal waters, dwarf minke whales have been recorded off most of the South Atlantic coast of South America (Baldas and Castello 1986, Zerbini et al. 1996), in the Beagle Channel (Chile/Argentina) (Acevedo et al. 2005), off South Africa (Best 1985), Australia (Arnold et al. 1987, Bannister et al. 1996, Arnold 1997), New Zealand (Dawson and Slooten 1990), and New Caledonia (Garrigue and Greaves 2001). The most northerly confirmed Southern Hemisphere record is from 2°S, off the northern coast of Brazil (Magalhães et al. 2007). Three dwarf minke whales were caught in whaling operations off Costinha, Brazil in 1980 (along with 900 Antarctic minke whales) (da Rocha and Braga 1982).
Countries:
Native:
Anguilla; Antarctica; Antigua and Barbuda; Argentina; Australia; Bahamas; Bangladesh; Belgium; Bermuda; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Brazil; Canada; Cape Verde; Chile; China; Cuba; Curaçao; Denmark; Dominica; Dominican Republic; Ecuador; Faroe Islands; France; French Guiana; Gambia; Greece; Greenland; Guadeloupe; Iceland; Indonesia; Ireland; Israel; Italy; Japan; Korea, Democratic People's Republic of; Korea, Republic of; Mauritania; Mexico; Morocco; Mozambique; Netherlands; Netherlands Antilles (Bonaire); New Caledonia; New Zealand; Norway; Papua New Guinea; Portugal; Puerto Rico; Russian Federation; Saint Martin (French part); Saint Pierre and Miquelon; Senegal; Sint Maarten (Dutch part); South Africa; Spain; Svalbard and Jan Mayen; Sweden; Taiwan, Province of China; Thailand; Tunisia; Turks and Caicos Islands; United Kingdom; United States; Uruguay; Virgin Islands, British; Virgin Islands, U.S.; Western Sahara
FAO Marine Fishing Areas:
Native:
Arctic Sea; Atlantic – northeast; Atlantic – northwest; Atlantic – western central; Atlantic – eastern central; Atlantic – southwest; Atlantic – southeast; Indian Ocean – eastern; Indian Ocean – western; Indian Ocean – Antarctic; Pacific – southwest; Pacific – southeast; Pacific – northeast; Pacific – Antarctic; Pacific – northwest; Pacific – eastern central; Pacific – western central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The IWC recognizes four stocks of Minke Whales in the North Atlantic: Northeast Atlantic, Central North Atlantic, West Greenland, and Canadian East Coast. The last includes the US east coast. Population estimates were last reviewed by the IWC SC in 2003 (IWC 2004a), but a new estimate for West Greenland was accepted in 2006 (IWC 2007a). The best/most recent available estimates are listed in Table 1 in the linked PDF document (which constitutes an integral part of this assessment). These total about 182,000.

No abundance estimate is available for the Newfoundland area where there was a small-scale fishery for Minke Whales during 1948-72 (Mitchell 1974).

Minke Whales have been exploited in the North Atlantic, mainly since the 1940s, and recorded catches total about 140,000 (IWC 2006a). The largest catches have been by Norwegian “small-type” whalers who have taken about 120,000 since 1948, mainly in the Northeast Atlantic. Annual catches peaked at over 4,000 in the late 1950s, declining to about 2,000 annually in the early 1980s. Catches were phased out from 1984 to 1987. Commercial minke whaling resumed in 1993 at a lower level and continues to the present.

About 4,000 Minke Whales were taken off Iceland during 1941-85, but recent abundance estimates imply that this would have had no discernible effect on the population. About 8,000 Common Minke Whales have been caught by small-type whaling off West Greenland, mainly since 1960. The present catch limits (up to 175 annually for the years 2003-7) were set by the IWC in the absence of advice from its SC. Some concerns have been expressed by the IWC SC over the sustainability of the catch levels given the uncertainty over the size of the population available to the hunters off West Greenland (IWC 2007a) although sex ratio information suggests that the population has not been significantly reduced by the catches (Witting 2006).

North Pacific
The IWC recognizes three management stocks in the North Pacific: Sea of Japan – Yellow Sea – East China Sea; Okhotsk Sea – West Pacific (west of 180°); and “Remainder” (east of 180°). Considerable research has been undertaken since the IWC designation indicating the potential for further stock structure both within the Okhotsk Sea - West Pacific area and in the "Remainder" area.

Okhotsk Sea – West Pacific
The IWC SC conducted an assessment of the Okhotsk Sea – West Pacific stock in 1991. Surveys in the summers of 1989 and 1990 yielded an abundance estimate of 25,049 (CV 0.316) of which the bulk (19,209; CV 0.339) was in the Okhotsk Sea (Buckland et al. 1992). Although the Okhotsk Sea was surveyed again in 1992 and 2003 (Miyashita 2004), an abundance estimate from the last of these surveys has yet to be presented.

About 13,000 Minke Whales have been recorded caught by Japanese coastal whaling during 1948-87 (IWC 2006a), of which probably all but about 1,000 were from the Okhotsk Sea-West Pacific stock. Annual catches peaked at over 500 in 1973, declining to 300 in 1987 when commercial whaling was suspended. Catches resumed in 1994 under scientific permits issued by the Government of Japan and have increased since then. The catch in 2006 was 195 from a permit for 220 (Miyashita and Kato 2007).

The above catch figures do not include net catches, which are not subject to whaling regulations. Reported net catches of minke whales off Japanese coasts averaged only about five per year in the 1980s, but Tobayama et al. (1992) estimated that the true level in 1989 was about 100. Based on genetic analysis of samples of whale products collected in commercial markets during 1993-1999, Baker et al. (2000) also estimated the net catch to be about 100 per year. During the 1990s, reported net catches averaged about 20 per year. After new regulations were introduced in 2001 that provided an incentive to report (only those catches that are reported and genetically sampled can be legally marketed), reported net catches have averaged 127 per year (Japan 2002-2006). About 55% of the reported net catches during 2001-05 have been on the Sea of Japan and East China Sea coasts (IWC 2007b), and would be mainly from the “J stock” (see below), with the remainder from the Okhotsk Sea-West Pacific Stock.

The issue of subpopulation structure within the Okhotsk Sea – West Pacific Stock has been discussed extensively by the IWC SC in the context of preparations for implementing the Revised Management Procedure (RMP) for western North Pacific Minke Whales, but with inconclusive results (IWC 2004b).

Although population models suggest that, when considered as a single biological unit, the Okhotsk Sea-West Pacific stock has declined little under the influence of past or present catches (IWC 2004c), the situation should be kept under review; in particular, the more recent 2003 survey data should be analyzed to update the 1990 and 1992 abundance estimates for the Okhotsk Sea.

Sea of Japan (East Sea) – Yellow Sea – East China Sea stock (“J stock”)
The reproductive cycle of this stock, usually referred to by biologists as the “J stock”, appears to be four months out of phase with other Northern Hemisphere minke whales, with conceptions occurring in October-November instead of February-March for the Okhotsk Sea – West Pacific stock (Omura and Sakiura 1956, Kato 1992). This is the only known case of breeding asynchrony in Baleen Whale populations from the same hemisphere. A degree of reproductive isolation between the two stocks is also suggested by frequency differences at selected allozyme loci (Wada 1984). A segregation of maternal lineages is indicated by marked differences in the frequencies of mtDNA haplotypes (Goto and Pastene 1997; Baker et al. 2000).

About 16,000 whales are recorded to have been taken from this stock by commercial whaling based in South Korea during 1940-86, in addition to about 1,000 from western Japan (IWC 2006a). Catches peaked at 1,033 in 1977. Catches were phased out with a complete moratorium to take effect from 1986 (IWC 1984).

However, net catches (which are not subject to whaling regulations) began in Korea in the late 1980s (Kim 1999). From 1996 onwards, a regulation has been in effect that requires the reporting of such catches. During 1996-2005, reported catches averaged 90 per year. However, a genetic analysis of samples of whale products on Korean commercial markets yielded an estimate of 827 (SE 164) whales entering the market in the period 1999-2003, as compared with a reported catch of only 458 whales (Baker et al. In press). This suggests that reporting is still far from complete, and that the total J-stock catch from South Korea and Japan (see above) has exceeded 200 per year over the last 10 years. Minke Whales are also reported to be a common bycatch in China, but no figures are available (IWC 2006c).

Surveys in the range of the J-stock have been conducted from 1999 in the waters of the Republic of Korea (Sohn et al. 2005) and from 2002 in Japanese waters (Miyashita 2004), but no estimate of total population size is available. The IWC in 2005 (IWC 2006b) endorsed plans for joint research by the range states (Republic of Korea, China, Japan, Russian Federation), and a comprehensive survey in the waters of all four countries is planned for 2007.

Eastern North Pacific (east of 180°E)
Population estimates are available only for parts of the eastern North Pacific, e.g. 1,015 (CV 0.73) for the west coast of the US during 1991-2001 (Anon. 2003) and 810 (CV 0.36) and 1003 (CV=0.26) respectively in the central and southeastern Bering Sea (Moore et al. 2002), and 1,232 (CV=0.34) for coastal waters of the northern Gulf of Alaska and the eastern and central Aleutian Islands (Zerbini et al., 2006). Minke Whales are apparently quite abundant in the offshore Gulf of Alaska (Miyashita et al. 1995) but no abundance estimate is available for that region.

Differences in vocalizations during the breeding season strongly suggest further population structure within this area. Different calls are found on either side of about 135 degrees W longitude (Rankin and Barlow 2005).

Southern Hemisphere
It is not possible at this time to estimate the abundance of B. acutorostrata in the Southern Hemisphere, because most of the available quantitative sighting data do not distinguish it from the much more numerous B. bonaerensis with which it is partially sympatric. B. acutorostrata has not been subject to significant exploitation in the Southern Hemisphere.

Generation time
No satisfactory method of age determination has been developed for this species to date. Therefore the value of 22 years from Taylor et al. (2007) was used. Unlike Antarctic Minke Whales, common minke whales tend not to develop ear plugs with readable layering (Lockyer 1984). A method based on layer counts in tympanic bullae (Christensen 1981) could not be reproduced by later workers. Other age-estimation methods are being investigated, but none is yet at the stage where it can be applied reliably to this species (Olsen and Øien 2002).
For further information about this species, see 2474_Balaenoptera_acutorostrata.pdf.
A PDF viewer such as Adobe Reader is required.
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: The Common Minke Whale occurs in both coastal and offshore waters and exploits a variety of prey species in different areas according to availability. In the Northern Hemisphere some populations migrate to higher latitudes in summer, but minke whales are also found year-round in some areas. With the exception of the Sea of Japan – Yellow Sea – East China Sea population, conception and birth occur in winter. Most animals occur singly, and few in groups of more than two.

In the North Atlantic, studies in the Barents and Norwegian Seas showed that minke whale diet varied greatly between areas and years, being dominated by krill in the northern areas, but by herring or capelin in other areas according to what was most abundant that year, with gadoids being taken when herring and capelin were scarce (Lindstrøm and Haug 2002). In the North Sea the diet consisted almost exclusively of sandeel (data from one year only). Minke whales taken off Iceland in 2003-04 contained mainly sandeel, with some capelin and gadoids (Víkingsson et al. 2006). Minke whales caught off Newfoundland during 1966-72 contained mainly capelin (Mallotus villosus) (Mitchell 1974).

In the Northwest Pacific, Lindstrøm et al. (1998) found that krill Euphausia pacifica dominated the diet in coastal areas and in the Okhotsk Sea, while in the offshore Pacific, Pacific saury Cololabis saira dominated.

Feeding habits of the Dwarf Minke Whale are poorly known. The stomach contents of an individual collected in Brazil contained exclusively Euphausia similis (Secchi et al. 2003). Whales taken in the Antarctic (n=16) ingested mostly myctophid fishes (Kato and Fujise 2000).
Systems: Marine

Use and Trade [top]

Use and Trade: This species was heavily hunted in the past, and harvesting is ongoing in parts of the North Atlantic and North Pacific.

Threats [top]

Major Threat(s): Whaling on this species has been intensive in the Northeast Atlantic, and it reduced the population over the period 1952-83. Catches were phased out by 1987, but whaling resumed, at a lower level, in 1993. Norway sets national catch limits based on the IWC’s Revised Management Procedure, a formula for setting safe catch limits (IWC 1999). In presenting the RMP to the IWC for approval, the IWC SC offered three variants that it believed were acceptable and the IWC chose the most conservative option. Up until 2000, Norway used this option to set its national catch limits. It is now using the least conservative option presented by the SC. The national catch limit for 2006 was 1,052 whales, but only 521 were taken.

Coastal catches averaged about 200 per year off Iceland until 1985 when the IWC moratorium on commercial whaling came into effect. Small (a total of 100 expected for the period 2003-2006) “experimental” catches resumed in 2003. Catches off West Greenland continue, under an IWC catch limit of 175 whales annually, valid through 2007. As discussed above the IWC SC has expressed concern at its inability to provide scientific advice on an appropriate catch limit (IWC 2007a).

Catches resumed in the North Pacific in 1994 under scientific permit issued by the Government of Japan, and have increased since. The catch in 2006 was 195 from a permit for 220 (Miyashita and Kato 2007).

Minke whales are subject to some level of incidental catch in fishing gear throughout much of their range, but in most areas the numbers involved are probably not significant. The exceptions are the coasts of Japan and Korea, and possibly China. In particular, the high level of net catches of the Sea of Japan-Yellow Sea-East China Sea population, likely over 200 per year, is a source of concern, which has prompted the IWC SC to conduct an in-depth assessment of this stock. A multinational survey involving the four range states is planned for 2007.

During this century, a profound reduction in the extent of sea ice in the Arctic is expected, and possibly a complete disappearance in summer, as mean Arctic temperatures rise faster than the global average (Anonymous 2005c). The implications of this for minke whales are unclear but warrant monitoring.

Conservation Actions [top]

Conservation Actions: Catch limits for all commercial whaling have been set at zero by the IWC since 1986. However, this moratorium does not apply to Iceland, Norway or the Russian Federation which have objected to this provision. IWC members are allowed to issue permits for whaling for scientific research, and Japan makes substantial use of this provision. Limited aboriginal subsistence whaling is permitted by the IWC for common minke whales off Greenland. Takes of dwarf minke whales have been excluded from the Japanese scientific whaling programme in the Antarctic (JARPA) since summer 1992/93 (Nishiwaki et al. 2005). Minke whales, including B. acutorostrata, are included in Appendix I of CITES, with the exception of the population from Greenland which is included in Appendix II. This implies prohibition of commercial international trade in products, but such prohibition does not apply to Iceland, Norway or Japan, who hold reservations on the species.

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. 2008. Balaenoptera acutorostrata. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 22 October 2014.
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