| Taxon ID: 6,499 Total records: 39,143 | ||||||||||||||
Balaenoptera musculus
Country
| Country | Viet Nam |
|---|---|
| Continent Ocean | Asia |
Classification
| Kingdom | Animalia (COL) |
|---|---|
| Phylum | Chordata (COL) |
| Class | Mammalia (COL) |
| Order | Cetacea (COL) |
| Family | Balaenopteridae (COL) |
Taxonomy
| Genus | Balaenoptera | Reference | |
|---|---|---|---|
| SubGenus | Vernacular Name | ||
| Species | musculus | IUCN Threat Status-Year | Endangered, 2018 |
| SubSpecies | Nat'l Threat Status-Year | Not Evaluated, 2000 | |
| Infraspecies | Reason for Change | ||
| Infraspecies Rank | subspecies | CITES | |
| Taxonomic Group | Mammals | Native Status | Native |
| Scientific Name Author | Linnaeus, 1758 | Country Distribution | Viet Nam |
| Citation | Description | Geographic Range [top]
Range Description:
The Blue Whale is a cosmopolitan species, found in all oceans but absent from some regional seas such as the Mediterranean, Okhotsk, and Bering seas. Until the 1960s, evidence of Blue Whale distribution came primarily from commercial catches, subsequently from whaling vessels sightings, then in the 1980s and 1990s from dedicated sighting surveys and platforms of opportunity, and since the 2000s also from acoustic detections, especially of males.
North Atlantic
In the North Atlantic the summer distribution of Blue Whales extends in the west from the Scotian Shelf to the Davis Strait (Canada/Greenland) and into the Gulf of Saint Lawrence (Sears and Calambokidis 2002, Waring et al. 2010). Blue whales occur in the Denmark Strait, around Iceland and north to the ice edge, and in the northeast to and around Svalbard (Norway), but not far into the Barents Sea. Historically, Blue Whales were commonly caught along the coasts of northern and western Norway, the Faeroes, and to the north and west of Scotland and Ireland. Small numbers were caught off northwestern Spain and near the Strait of Gibraltar, but the species does not occur in the Mediterranean (Reeves and Notarbartolo di Sciara 2006).
The winter distribution is poorly known but Blue Whales may have been dispersed over much of the tropical and subtropical North Atlantic (Reeves et al. 2004). There have been winter sightings off the coast of Mauritania (Baines and Reichelt 2014). Blue Whales are regularly observed around the Azores in spring and at least some migrate northward from there (Silva et al. 2013). Blue Whales have been tracked from the Gulf of Saint Lawrence to the New England Seamounts and to the coasts of North and South Carolina (34°N) in winter (Lesage et al. 2017). There are virtually no records from the Gulf of Mexico or the Caribbean.
Photo-identification data show that there are two largely separate populations in the North Atlantic: the northwest Atlantic population occurs in summer in the Gulf of Saint Lawrence, on the Scotian Shelf, and around Newfoundland and west of Greenland. The northeast Atlantic population occurs in summer east of Greenland, around Iceland, Jan Mayen and Svalbard, and west of Ireland; in spring it occurs around the Azores and in winter off northwest Africa. About 500 individuals have been identified to date in each of the two populations, but so far only one crossover (from the Gulf of Saint Lawrence to the Azores) has been documented through photographic matching (Sears et al. 2015.
North Pacific
Blue Whales occur in summer north of 35°N in the western North Pacific, and north of 40°N in the central North Pacific and Gulf of Alaska, but not in the Bering or Okhotsk Seas. In the eastern North Pacific, they occur year-round off Baja California, Mexico, and the California coast (Calambokidis and Barlow 2004). Analysis of song types suggest that Blue Whales in the eastern North Pacific are a separate population from those in the central and western North Pacific, but that whales from the eastern population mingle with whales from the western population in the Gulf of Alaska in summer (Monnahan et al. 2014). While some Blue Whales remain off California in winter, some of the Californian Blue Whales, including females with or without calves, migrate into the Gulf of California in winter (Sears et al. 2013). Some North Pacific Blue Whales migrate in winter to the Costa Rica dome (Mate et al. 1999) and perhaps further south into Peruvian waters (Le Duc et al. 2017).
Eastern tropical Pacific (ETP) and eastern South Pacific
Blue Whales are present year-round on the Costa Rica Dome but it is unclear whether any animals are resident there, or whether it is sequentially occupied by whales wintering from the northeastern and southeastern Pacific (Reilly and Thayer 1990).
Sightings recorded by whalers taking other species show that Blue Whales were quite abundant during 1976-82 in the waters west of northern Peru (exact locations not given), especially in January-March, but with much reduced presence during the severe El Niño event of 1982-83 (Valdivia et al. 1984, Donovan 1984). Their presence in November-December from the coast out to well beyond the Galápagos Islands was also shown by sightings from Japanese scouting vessels during 1979-82 (Miyashita et al. 1996). Their presence in the waters of Ecuador and Peru was shown by tuna vessel surveys during October-March 1975-88 (Reilly and Thayer 1990) and later by dedicated cetacean surveys in July-December during 1986-2003 (Hamilton et al. 2009).
Blue Whales have been hunted in the past from several locations on the Chilean coast from 20°S to 42°S in all seasons (Allison 2017). Current areas of regular summer abundance include Chañaral (29°S) and Chiloé Island (42°-44°S) (Hucke-Gaete et al. 2004, Vernazzani et al. 2012). A summer survey in December-January 1997/98 of offshore waters 12-200 nm from the coast between 18°S and 38°S showed presence from 20°S southward, with most sightings between 27°S and 33°S (Williams et al. 2011).
Based on morphology, genetics and migration, Branch et al. (2007a) proposed that Chilean Blue Whales are a separate subspecies from B. m. intermedia and B. m. brevicauda. However, while Chilean Blue Whales are clearly distinct from the other Southern Hemisphere subspecies, the division between Chilean and North Pacific Blue Whales is not yet clear. LeDuc et al. (2017) found that most Blue Whales biopsy sampled during July-November on the Costa Rica Dome were genetically closer to whales sampled in the North Pacific, while most Blue Whales biopsy sampled in the same months off Ecuador and the Galápagos were genetically closer to whales sampled in Chilean waters, but there was a high degree of uncertainty in individual assignments to the two groups. There is movement between the two grounds, with individual whales matched or tracked between California and the Costa Rica Dome, between the Costa Rica Dome and the Galápagos, and between the Galápagos and southern Chile (IWC 2017a, Huecke-Gate et al. 2016). In Chilean waters, the seasonal distribution of acoustic detections suggests a migration to northerly tropical latitudes in winter, but calls typical of Chilean Blue Whales were also recorded year-round in the ETP (Buchan et al. 2015). Calls typical of Antarctic Blue Whales are detected in the ETP during the austral winter (Stafford et al. 1999, IWC 2017a). Clearly more research is needed to clarify the seasonal presence and distribution of the different groups of Blue Whales in the ETP, as the area is used by North Pacific, Chilean, and Antarctic Blue Whales, and there may also be resident individuals.
Calls typical of Antarctic Blue Whales have also been detected from January to June near Chiloé Island, but appeared to be from individuals making only brief visits to the area (Buchan et al. 2018).
Southern Indian Ocean and southwestern Pacific
Pygmy Blue Whales (B. m. brevicauda) occur north of 52°S, with very few or no individuals south of this latitude (Branch et al. 2007a, 2009). They occur off northwestern Madagascar (Cerchio et al. 2016), on the Madagascar plateau (Best et al. 2003), in the offshore waters of Kenya (Barber et al. 2016) around and north of the Seychelles (Mikhalev 2000), across the pelagic southern Indian Ocean, and off South Australia and Western Australia, where they form part of a more or less continuous distribution from Tasmania to Indonesia. The Blue Whales observed around New Zealand also appear to be Pygmy Blue whales, based on genetics (Sremba et al. 2015) and morphology (Olson et al. 2015). Blue Whales appear to be rare or absent in the central South Pacific between the New Zealand and Chilean areas of occurrence (Branch et al. 2007b).
Based on acoustic detections, Antarctic Blue Whales (B. m. intermedia) occur in the tropical and subtropical Indian Ocean only in winter and spring, while Pygmy Blue Whales occur year-round but with a tendency to move southward in the austral summer (Samaran et al. 2013). Other data are also broadly consistent with a lower-latitude distribution in the austral winter and a more southerly distribution in summer (Zemsky and Sazhinov 1982, cited by Best et al. 2003): Pygmy Blue Whales were present at the Seychelles in November but not April (Mikhalev 2000), and off Kenya in September and October but not during November to January (Barber et al. 2016). Foetuses found in the Pygmy Blue Whales taken by Soviet whalers near the Seychelles and in the southern Indian Ocean indicated that calves are born in the austral winter (Mikhalev 2000).
Northern Indian Ocean
Blue Whales are found year-round in the northern Indian Ocean, especially around Sri Lanka, and seasonally around the Maldive Islands and in the Gulf of Aden (Alling et al. 1991, Mikhaelev 2000, Stafford et al. 2011, Anderson et al. 2012). They occur virtually year-round off southern Sri Lanka but are most abundant during December to May and least abundant during July to September (Randage et al. 2014). Analyses of fetuses in Blue Whales taken by Soviet fleets in the Northern Indian Ocean (Mikhalev 2000) revealed no clear seasonality of reproduction, being consistent either with year-round reproduction or perhaps a bimodal pattern.
Anderson et al. (2012) considered that there is some east-west migration within the northern Indian Ocean, with peak occurrence in the western Arabian Sea in May-October, followed by dispersal eastward after the end of the southwest monsoon, past Sri Lanka and into the Bay of Bengal, with peak abundance northeast of Sri Lanka occurring in February and March. However, Samaran et al. (2013) found that call types detected off Sri Lanka were also heard in the southern Indian Ocean in December and January, at least as far south as 43°S, which suggests that some Blue Whales may migrate between Sri Lanka and the temperate southern Indian Ocean.
Although Blue Whales in the northern Indian Ocean are tentatively considered to be the distinct subspecies B. m. indica, their distinction from B. m. brevicauda is unclear. Mikhalev (2000) found the maximum body length, body length at maturity, and ovulation rate of Arabian Sea Blue Whales to be similar to Pygmy Blue Whales in the Southern Indian Ocean.
Antarctic and Southern Ocean
The Antarctic form B. m. intermedia, occurs throughout the Antarctic in summer, from the Antarctic Polar Front up to and into the sea ice, and in the subantarctic South Atlantic including the South Georgia area (Branch et al. 2007b). The winter distribution is not well known, but at least some and possibly most of the population migrates to lower latitudes in winter. Evidence for this comes from past catches of Antarctic-sized Blue Whales off Angola, Namibia, and South Africa in winter only (Branch et al. 2007b) and more recently from acoustics: call types characteristic of Antarctic Blue Whales have been recorded in the austral winter just north of the equator in the mid-Atlantic (Samaran et al. 2017), in the southeastern Atlantic on the west coast of South Africa (Bell 2016 ), in the tropical Indian Ocean and southwest Pacific Ocean (Balcazar et al. 2017), and near the Galápagos Islands (Stafford et al. 2004). However, there is also at least some winter presence in high latitudes (?irovi? et al. 2009, Thomisch et al. 2016) and perhaps some summer presence in mid-latitudes of the Indian Ocean (Samaran et al. 2013) and southeastern Pacific (Buchan et al. 2018).
Countries occurrence:
Native:
Angola; Argentina; Australia; Bangladesh; Bermuda; Brazil; Cabo Verde; Canada; Chile; Cocos (Keeling) Islands; Colombia; Comoros; Cook Islands; Costa Rica; Djibouti; Ecuador; El Salvador; Falkland Islands (Malvinas); Faroe Islands; Fiji; France; French Southern Territories; Greenland; Guatemala; Iceland; India; Indonesia; Iran, Islamic Republic of; Ireland; Japan; Kenya; Kiribati; Madagascar; Malaysia; Maldives; Mauritania; Mauritius; Mexico; Morocco; Mozambique; Myanmar; Namibia; Nauru; New Caledonia; New Zealand; Nicaragua; Norfolk Island; Norway; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Portugal (Azores, Madeira); Réunion; Russian Federation (Kamchatka, Kuril Is.); Saint Pierre and Miquelon; Senegal; Seychelles; Solomon Islands; Somalia; South Africa; South Georgia and the South Sandwich Islands; Spain (Canary Is.); Sri Lanka; Svalbard and Jan Mayen; Tanzania, United Republic of; Thailand; Timor-Leste; Tuvalu; United Kingdom; United States; Uruguay; Vanuatu; Western Sahara; Yemen
Vagrant:
Iraq
FAO Marine Fishing Areas:
Native:
Arctic Sea; Atlantic – northwest; Atlantic – southwest; Atlantic – eastern central; Atlantic – northeast; Atlantic – southeast; Atlantic – Antarctic; Atlantic – western central; Indian Ocean – western; Indian Ocean – eastern; Indian Ocean – Antarctic; Pacific – western central; Pacific – northeast; Pacific – Antarctic; Pacific – northwest; Pacific – eastern central; Pacific – southeast; Pacific – southwest
Additional data:
Range Map: Click here to open the map viewer and explore range.
Population [top]
Population:
North Atlantic
Nearly 11,000 Blue Whales were specifically recorded as taken in the North Atlantic since the start of modern whaling in northern Norway in the 1860s, but an additional 13,000 unspecified large whales were recorded as caught in the late 19th and early 20th centuries (Allison 2017), of which perhaps 30% could have been Blue Whales based on specified catches in the same areas in the same and following years. In addition, whaling in the earlier years (pre-1916) is thought to have involved substantial struck-and-lost rates (IWC 2010, 2017b) such that the total number of Blue Whales killed in the North Atlantic was probably in the range 15-20,000.
Catches started off the coast of Finnmark, northern Norway, where it is likely that over 3,000 Blue Whales were taken before whaling was banned from mainland Norway in 1905. Operations spread to Svalbard, where over 1,000 Blue Whales were taken, and to Iceland where probably over 5,000 were taken before whaling was banned for about 20 years starting in 1916 due to noticeably declining abundance. Over 2,000 Blue Whales were taken off Newfoundland, about 500 in the Gulf of St Lawrence and nearly 1,000 around the Faeroes, Scotland, and Ireland. Very few Blue Whales were caught off Spain and Portugal. After the main period of whaling, low-level catches throughout the range probably impeded recovery until catches all but ceased around 1960. The last recorded directed catches were six Blue Whales taken off Spain in 1978, three by pirate whaling vessels, and three by catchers boats working for land stations (Allison 2017).
Post-whaling abundance estimates for the central and eastern North Atlantic (Iceland, Denmark Strait, southeastern Greenland, Jan Mayen, Faeroes and the British Isles and the Norwegian and Barents Seas) rose from 298 (coefficient of variation (CV) 0.25) in 1987 to 1,012 (CV 0.23) in 2001 (Pike et al. 2009). The increasing trend is consistent with a previous trend detected in sighting rates from Icelandic whaling vessels during 1969-88 (Sigurjónsson and Gunnlaugsson 1990). The Blue Whales in these surveys were most abundant west of Iceland, but with a shift to the northeast of Iceland in recent years (Víkingsson et al. 2015) and around Jan Mayen and Svalbard. Blue Whales are now very rare along the coast of Norway despite large catches there in the past. Further surveys of this area were conducted in 2007 and 2014-16 but the data have not yet been analysed to produce updated estimates of Blue Whale abundance (NAMMCO 2017).
Too few Blue Whales were observed in a survey of the Canadian Atlantic in 2007 to estimate abundance (Lawson and Gosselin 2009) and none were seen in US waters in 2011 surveys (Palka 2012).
Only one Blue Whale was seen (west of Cap Finisterre) during the summer 2016 SCANS III surveys which covered UK waters, the North Sea, English Channel, Bay of Biscay, and the Atlantic waters of France and Spain (Hammond et al. 2017). By comparison, over 1,000 Fin Whales (Balaenoptera physalus) were seen. These results suggest a Blue Whale summer abundance in the area only in the tens. A separate survey of waters south-west of Ireland in 2013 (Baines et al. 2017) recorded16 Blue Whales (including resightings), and the data suggest that about 10-20 individuals were present. A Blue Whale seen in southeastern Biscaya in 2016 was the first live sighting off Spain since the last catches in the 1970s (Covelo et al. 2017).
About 500 individual Blue Whales were photo-identified in the Gulf of Saint Lawrence during 1979-2015 (Sears et al. 2015). In view of the long time period, many of the animals in the catalogue are likely no longer alive. The Northeast Atlantic photo-id catalogue contained over 500 individuals by 2015, including 125 collected off Iceland during 1995-2005 and 335 in the Azores during 2002-15. The catalogues have not yet yielded estimates of abundance.
North Pacific
About 9,000 Blue Whales were recorded as caught in the North Pacific, in addition to over 7,000 unspecified whales, some of which would have been Blue Whales (Allison 2017). The Blue Whale was protected by the International Whaling Commission (IWC) from 1966, but a further 760 Blue Whales were taken illegally by USSR fleets until 1972 (Doroshenko 2000, Ivashchenko et al. 2017)
The best estimate of abundance for the eastern North Pacific population, from photographic capture-recapture with an allowance for heterogeneity, is 1,647 (CV 0.07) (Calambokidis and Barlow 2013). Using the estimated catch history, including the assignment of a portion of the past catches in the Gulf of Alaska to the eastern North Pacific population, Monnahan et al. (2015) concluded that the eastern North Pacific population had recovered to near its pre-whaling abundance, estimated to be 1,750-2,500 whales. The population seems to have been roughly stable since the early 1990s (Carretta et al. 2017).
The international POWER (Pacific Ocean Whale and Environment) surveys covered the North Pacific east of 170°E and north of 40°N up to the Aleutian chain and the Alaska coast during 2010-12 (IWC 2018a). A total of 16 Blue Whales were seen. No abundance estimate has been calculated but the survey results suggest an abundance in the range 500-1,500, but which possibly includes some of the animals that are included in the above mark-recapture estimate. Only one Blue Whale was seen during the 2013-16 POWER surveys which covered the area between 20°N and 40°N. No Blue Whales were sighted in surveys of coastal British Columbia waters during 2004-08 (Best et al. 2015).
In the northwestern Pacific, Hakamada and Matsuoka (2016) estimated the late summer abundance in 2008 west of 170°E and north of 35°N at about 1,000 whales (CV ~0.5). The survey did not include the waters within the Russian Exclusive Economic Zone along the Kuril chain and Kamchatka, where Blue Whales also occur in summer (Miyashita 2006).
Blue Whales remain rare or absent in the Bering and Okhotsk Seas (Miyashita et al. 1996, Miyashita 2006, Friday et al. 2013), and very few historical catches are recorded from these areas.
Although over 2,000 Blue Whales were taken by coastal whaling in Japan until the 1960s, no Blue Whales were seen around Japan and in the North Pacific west of 155°E in extensive scouting vessel surveys during 1964-90 (Miyashita et al. 1996). Blue Whales were seen from 145°E eastward in surveys conducted during 1994-2015, but not near the coast of Japan (Matsuoka et al. 2016).
Eastern South Pacific and eastern equatorial Pacific
A total of 5,276 Blue Whales were reported as caught in the eastern South Pacific including equatorial waters in the 20th century (Allison 2017). Allowing for some Blue Whales among the unspecified catches and for some level of struck and lost animals, and a lack of catch records for some whaling operations, the likely total kill is in the range 6,000-7,000. However, about 1,000 animals which were taken in equatorial waters during the austral summer/northern winter may have consisted partly of animals from the North Pacific populations. Furthermore, in the first half of the 20th century, Antarctic Blue Whales were much more abundant than today, hence a significant portion of early catches off Peru and Chile, especially in the austral winter, may have been of Antarctic Blue Whales.
For the first 60 years of modern whaling, catches of Blue Whales off Chile and Peru averaged only 60 per year but catches increased from 1964 for meat exports, and 964 whales were taken during 1964-67, between 19°-39°S. Following a recommendation by the Comisión Permanente del Pacífico Sur (the international body responsible for regulating whaling in the southeastern Pacific at the time) (CPSS 1966) catching of Blue Whales were suspended in Peru after the 1966 season and in Chile after the 1966/67 season. Clarke et al. (1978) cited the high catches off Peru and Chile at a time when the Antarctic Blue Whale stock was reduced to less than 1,000, as evidence that the Chilean and Peruvian whales were not from the Antarctic population, an observation that was later confirmed (see Geographic Range above). Sighting rates of Blue Whales from Peruvian and Chilean whaling vessels apparently remained reasonably high after catches of this species ceased (Valdivia et al. 1984, Maturana 1982), but the high catches of the mid-1960s would probably have been unsustainable if they had been allowed to continue.
A survey conducted under the IDCR (International Decade of Cetacean Research) programme in November-December 1982 between 10°S and 10°N from the coasts of Peru and Ecuador out to 110°W resulted in 16 Blue Whale sightings, all within 100 nm of the coast (Donovan 1984), but the survey coincided with the onset of an especially severe El Niño event.
A survey conducted under the international SOWER (Southern Ocean Whale and Environmental Research) programme during December-January 1997/98 covered the area between 12-200nm off the Chile coast between 18°S and 38°S and resulted in an abundance estimate of 303 Blue Whales (95% confidence interval (CI) = 176-625) for this area (Williams et al. 2011). Most Blue Whale sightings were between 27°S-33°S. A mark-recapture estimate using photo-id data collected around Chiloé Island (42°S) during 2004-11 yielded an estimate of 450 whales (CV 0.17) in 2008 with no significant trend (Cooke and Jackson 2017) but it is unclear what population this estimate pertains to because it includes both resident and transient individuals. Only one match was found between the 23 “individuals” (actually: left or right sides) identified on the SOWER cruise and the 563 “individuals” identified around Chiloé Island (IWC 2017a), which suggests that the whales either belong to distinct groups or to quite a large common population. Likewise, only one match was found between the Chiloé whales and the Blue Whales individually identified off Chañaral (29°S) (Galletti Vernazzani et al. 2017). The overall abundance and trend of Chilean Blue Whales is currently uncertain. Williams et al. (2011 revised 2017) show possible population trajectories from the early 20th century to the present.
Southern Indian Ocean and Southwest Pacific
No comprehensive estimate of the population of Pygmy Blue Whales is available. From a survey in December 1996, Best et al. (2003) estimated the abundance of Pygmy Blue Whales in a survey area south of Madagascar to be 424 (confidence limits about 190-930) and suggested, based on the distribution of past catches, that the total population in the southwestern Indian Ocean was about three times that in the survey area. The Western Australia population has been estimated at 662-1,559 based on acoustic recordings during 2000-2006 (McCauley and Jenner 2010), and 712-1,754 based on photo-identification during 2000-2005 (Jenner et al. 2008). However, these estimates do not cover the full range of the species in the southeastern Indian Ocean, and updated estimates based on photo-identification and genetic recapture are in preparation (IWC 2017a). A total of 31 distinct blue whales were identified in New Zealand waters during 2004-2014 (Olson et al. 2015) and a population estimate is currently in preparation. The catch of over 9,500 Pygmy Blue Whales in the southern Indian Ocean in the period 1960-72 (Allison 2017) suggests that the initial population was at least this size, and hence that the current population is still depleted, but not as severely as that of the Antarctic Blue Whale.
Northern Indian Ocean
Mikhalev (2000) documented 1,294 Pygmy Blue Whales caught illegally by Soviet fleets in the northern and equatorial Indian Ocean during 1963-66, mainly in the Gulf of Aden, north of the Seychelles, off the Maldive Islands and Laccdive Islands, and west of southern India and Sri Lanka. Priyadarshana et al. (2016) estimated a population size of 270 whales (CV 0.09) in a 7,500 km² area off southern Sri Lanka, which probably does not cover the full extent of this area of occurrence. No other abundance estimates in the Northern Indian Ocean are available.
Antarctic
Catch records did not distinguish between subspecies until biologists accompanying Japanese and Russian whaling fleets started recording them separately from the 1960s (Ichihara 1966, Doroshenko 2000). Branch et al. (2009) concluded that virtually all of the Blue Whales taken south of 52°S in the southern Indian Ocean sector were Antarctic Blue Whales. The catch history of the various subspecies can be approximately reconstructed by assuming that Blue Whales not specified to subspecies taken south of 52°S or in the South Atlantic were B. m. intermedia, that Blue Whales taken off the west coast of South America were Chilean Blue Whales, and that Blue Whales not specified to subspecies taken in the northern Indian Ocean or in the Indian Ocean or the western South Pacific north of 52°S in the austral summer were Pygmy Blue Whales (understood here to include both B. m. brevicauda and B. m. indica). This leaves just a few hundred early catches in the southern Indian Ocean of doubtful identity. Allowing for some of the unspecified (to species) catch to have been Blue Whales, and for some struck and lost whales in the early years, the estimated total historical kill is about 350,000 Antarctic Blue Whales and 14,000 Pygmy Blue Whales (B .m. brevicauda and/or B. m. indica). These figures include the approximately 9,400 Blue Whales taken illegally by Soviet fleets in the 1960s and early 1970s that were not reported at the time (Ivashchenko et al. 2011), of which about 80% were Pygmy Blue Whales based on the above criteria.
The most recent circumpolar estimate of abundance for Antarctic Blue Whales agreed by the IWC Scientific Committee is 2,280 (CV 0.36) in 1998, based on sightings south of 60°S in summer, with an estimated annual increase rate of 8.1% (95% CI 1.6%-14.9%) (Branch 2007). A recalculation of the increase rate using more years of data is in progress (IWC 2017a).
An estimate from Japanese surveys covering just half of the Antarctic (35°E to 145°W) south of 60° S is 1,223 (CV 0.35) in 2008, with an estimated annual increase rate reported as 8.3% (95% CI 3.9% - 12.5%) (Matsuoka and Hakamada 2014). However, the annual increase rate implied by the presented data is 6.6% with a wide confidence interval (95% CI 0.0%-13.2%).
Photo-identification of Antarctic Blue Whales during 1991-2016 yielded 441 distinct individuals of which 14 were re-sighted in different years (Olson et al. 2016). The number of inter-annual re-sightings is too small for reliable estimation of abundance and trends, but is broadly consistent with the above circumpolar abundance estimate.
Assessment
The IWC Scientific Committee in 2008 accepted a stock assessment of Antarctic Blue Whales by T. Branch (IWC 2009). However, the assessment is redone here because the Committees assessment did not use an age-structured model and thus could not estimate the numbers of mature individuals that are required for the IUCN Red List assessment. The historical catch data have also been revised since then (Allison 2017).
The age at first reproduction is not well-known for Blue Whales in general, but Sears et al. (2013) found a youngest age of 11 years for first known calvings of female Blue Whales in the eastern North Pacific. This agrees with the estimate of 11 years by Taylor et al. (2007) from inter-specific comparisons. The generation time was estimated by Taylor et al. to be 30.8 years, which corresponds to a 3-generation period from 1926-2018 for application of the A criterion for the Red List.
Plausible rates of natural increase, taking into account the age at maturity and reproductive rates have been estimated to be 4.1% per year (Branch 2008a) for Antarctic Blue Whales and 2% per year for Pygmy Blue Whales, which appear to have a lower reproductive rate (Branch 2008b). Taylor et al. (2007) inferred an intrinsic increase rate of 5% for Blue Whales and estimated the proportion mature to be 72% for a stable population or 48% for a population increasing at the intrinsic rate.
For Antarctic Blue Whales, a 5% intrinsic increase rate with logistic density-dependence, and assuming a 5 year mean age at recruitment, as for Fin Whales, an annual natural survival rate of 0.975 (Ramp et al. 2006, Taylor et al. 2007), and a total population size of 2,280 whales in 1998, would imply a mature population size in 1926 of 125,000 or a total population size of 189,000, declining to a minimum of less than 1,000 in the late 1960s, and increasing to about 3,000 mature or 6,500 total by 2018 (see Supplementary Information).
As discussed above, there are no complete estimates of recent or current abundance for the other regions, but plausible total numbers would be 1,000-3,000 in the North Atlantic, 3,000-5,000 in the North Pacific, and possibly 1,000-3,000 in the eastern South Pacific. The number of Pygmy Blue whales is very uncertain but may be in the range 2,000-5,000. Taken together with a range of 5,000-8,000 in the Antarctic, the global population size in 2018 is plausibly in the range 10,000-25,000 total or 5,000-15,000 mature, compared with a 1926 global population of at least 140,000 mature. The current mature population would therefore be between 3 and 11% of the 1926 level. This overlaps the boundary (90% decline or 10% remaining) between the Endangered and Critically Endangered categories under criterion A1.
There is evidence of increasing abundance, at least up to around the year 2000, in the Antarctic and North Atlantic, and at least stability in the North Pacific. There is as yet no evidence of trend in the abundance of Pygmy Blue Whales or of Chilean Blue Whales, but it is likely that the global population of Blue Whales has increased in recent decades.
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Current Population Trend: Increasing
Additional data:
? Number of mature individuals: 5000-15000 ? Continuing decline of mature individuals: No
? Extreme fluctuations: No ? Population severely fragmented: No
Habitat and Ecology [top]
Habitat and Ecology:
Blue Whales feed almost exclusively on euphausiids (krill), with a variety of species being taken by different Blue Whale populations, such as Euphausia superba in the Antarctic, Nyctiphanes australis off southern Australia (Gill 2002), Euphausia recurva off Western Australia (J. Bannister pers. comm. 2007), Nyctiphanes simplex off the Galápagos (Palacios 1999), Euphausia pacifica and Thysanoessa spp. in the North Pacific (Fiedler et al. 1998), and Meganyctiphanes norvegica and Thysanoessa spp. in the North Atlantic (Visser et al. 2011, McQuinn et al. 2016). They feed both at the surface and at depths of up to 300 m (Sears and Calambokidis 2002, Calambokidis et al. 2007).
The migration patterns of Blue Whales are not well understood, but appear to be diverse. Although there is evidence of migratory behaviour in most of the populations studied, both wintering and summering areas appear to be occupied at some level throughout the year. Some individuals may reside year-round in habitats of year-round high productivity, while others undertake long migrations from tropical waters to high-latitude feeding grounds, but possibly stopping to feed in areas of high productivity on route, while yet others may undertake more limited migrations (Branch et al. 2007b, Gill et al. 2011, de Vos et al. 2014, Silva et al. 2013, Torres 2013, Lesage et al. 2017).
Systems: Marine
Continuing decline in area, extent and/or quality of habitat: Unknown
Generation Length (years): 30.8
Use and Trade [top]
Use and Trade: The Blue Whale was the subject of major commercial hunting in the past, which ceased in the 1970s.
Threats [top]
Major Threat(s):
The main threat to Blue Whales in the past was direct exploitation, which only became possible on a regular basis in the modern era using deck-mounted harpoon cannons. Modern Blue Whale hunting started in the North Atlantic in 1868 and spread to other regions after the northeastern Atlantic population had been severely reduced, and whaling was temporarily banned in Norway from 1905 and in Iceland from 1915 (Tønnessen and Johnsen 1982). The Antarctic and North Atlantic populations were each probably depleted to the low hundreds by the time whaling ceased in the 1960-1970s, but have increased since. Blue Whales have been legally protected worldwide since 1966, although they continued to be caught illegally by former USSR fleets until 1972. The last recorded deliberate catches were off Spain in 1978 (Allison 2017).
Blue Whales in a calving ground off southern Sri Lanka appears to be especially subject to ship strikes, as indicated by both direct observations of strikes and strandings that exhibit blunt trauma (Ilangakoon 2012, de Vos et al. 2016) and observations of living animals that appear to have injuries that prevent normal swimming (IWC 2018b). The large volume of ship traffic around the southern coast of Sri Lanka makes it one of the busiest ocean-going shipping lanes in the world, but Priyadasharnha et al. (2016) showed that the expected frequency of ship strikes on Blue Whales would be greatly reduced by moving the lanes slightly further offshore.
Nine deaths of Blue Whales plus some serious injuries were attributed to ship strikes on the west coast of North America during 2007-13 (Carretta et al. 2017). Of 21 carcasses of Blue Whales found off California during 1988-2007, eight were found to have been killed by ship strike (Berman-Kowalewski et al. 2010). This suggests that ship strikes represent a substantial addition to natural mortality (Rockwood et al. 2017). Monnahan et al. (2015), on the other hand, argued that ship strikes have only a small effect on this population. As of 2018 this issue had not been resolved.
Of the Blue Whales in the Gulf of Saint Lawrence photo-identification catalogue, 16% appear to have scars or wounds resulting from ship strikes (Sears and Calambokidis 2002).
McKenna et al. (2015) concluded from tracking data that Blue Whales do not demonstrate effective avoidance behaviour when ships are near. However, Priyardashana et al. (2016) showed, based on densities of whales and shipping, that the expected frequency of ship strikes off southern Sri Lanka would be an order of magnitude higher than current estimates if the Blue Whales took no evasive action.
Incidental catches of Blue Whales in fisheries appear to be rare. The only reported cases this century were one in the northeastern Pacific in 2015 and one in the Gulf of Saint Lawrence in 2002. Blue whales in cold waters often have marks or scars caused by contact with ice, which can make it harder to identify scars caused by contact with fishing gear.
The main food of Antarctic Blue Whales, Euphausia superba and E. crystallorophias, are predicted to decline during the 21st century due both to reduced ocean productivity associated with warming (Piñones and Fedorov 2016) and to increasing ocean acidity that limits their shell-building (Kawaguchi et al. 2013). Comparable changes are likely in other oceans.
Conservation Actions [top]
Conservation Actions:
Blue Whales have been protected from commercial hunting by the International Whaling Commission since 1966, although illegal catches by USSR fleets continued until 1972. No Blue Whales have been reported as having been caught deliberately since 1978. The species is on Appendix I of both the Conservation on International Trade in Wild Species of Fauna and Flora (CITES) and the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
Citation: Cooke, J.G. 2018. Balaenoptera musculus. The IUCN Red List of Threatened Species 2018: e.T2477A50226195. http://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T2477A50226195.en. Downloaded on 07 January 2019.
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Additional Info
Synonyms To Manage Synonyms for Balaenoptera musculus, click this link: Synonyms. |
Balaena musculus Linnaeus, 1758 ¦ Sibbaldius sulfureus Cope, 1869 ¦ |
Common Names To Manage Common Names for Balaenoptera musculus, click this link: Common Names. |
Blue Whale () |
Localities To Manage Localities for Balaenoptera musculus, click this link: Localities. |
Species Record Updated By:
Carlos Aurelio Callangan
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