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Blue whale
Scientific classification

</ref>[1] In the North Pacific Euphausia pacifica, Thysanoessa inermis, Thysanoessa longipes, Thysanoessa spinifera, Nyctiphanes symplex and Nematoscelis megalops;[2][3][4] in the Antarctic Euphausia superba, Euphausia crystallorophias and Euphausia valentin.

The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3,600 kg (8,000 lb) of krill in a single day.[5] This means that they typically feed at depths of more than 100 m (330 ft) during the day, and only surface feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 20 minutes are common. The longest recorded dive is 36 minutes (Sears 1998). The whale feeds by lunging forward at groups of krill, taking the animals and a large quantity of water into its mouth. The water is then squeezed out through the baleen plates by pressure from the ventral pouch and tongue. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. The Blue Whale also incidentally consumes small fish, crustaceans and squid caught up with krill.[6][7]

Life history

A juvenile Blue Whale with its mother

Mating starts in late autumn, and continues to the end of winter.[8] Little is known about mating behaviour or breeding grounds. Females typically give birth once every two to three years at the start of the winter after a gestation period of ten to twelve months.[8] The calf weighs about two and a half tonnes (2.75 short tons) and is around 7 m (23 ft) in length. Blue Whale calves drink 380–570 litres (100–150 US gallons) of milk a day. Weaning takes place for about six months, by which time the calf has doubled in length. Sexual maturity is typically reached at eight to ten years by which time males are at least 20 m (70 ft) long (or more in the Southern Hemisphere). Females are larger still, reaching sexual maturity at around the age of five, by which they are about 21 m (69 ft) long.

Scientists estimate that Blue Whales can live for at least 80 years;[9][10][8] however, since individual records do not date back into the whaling era, this will not be known with certainty for many years. The longest recorded study of a single individual is 34 years, in the north-east Pacific (reported in Sears, 1998). The whales' only natural predator is the Orca.[11] Studies report that as many as 25% of mature Blue Whales have scars resulting from Orca attacks.[9] The rate of mortality due to such attacks is unknown.

Blue Whale strandings are extremely uncommon, and, because of the species' social structure, mass strandings are unheard of.[12] However when strandings do occur they can become the focus of public interest. In 1920, a Blue Whale washed up near Bragar on the Isle of Lewis in the Outer Hebrides of Scotland. It had been shot in the head by whalers, but the harpoon had failed to explode. As with other mammals, the fundamental instinct of the whale was to try to carry on breathing at all costs, even though this meant beaching to prevent itself from drowning. Two of the whale's bones were erected just off a main road on Lewis, and remain a tourist attraction.[13]

Vocalizations

See also: Whale song
Multimedia relating to the Blue Whale
Note that the whale calls have been sped up 10x from their original speed.
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Estimates made by Cummings and Thompson (1971) suggest that source level of sounds made by Blue Whales are between 155 and 188 decibels when measured relative to a reference pressure of one micropascal at one metre.[14][15] All Blue Whale groups make calls at a fundamental frequency of between 10 and 40 Hz, and the lowest frequency sound a human can typically perceive is 20 Hz. Blue Whale calls last between ten and thirty seconds. Additionally Blue Whales off the coast of Sri Lanka have been recorded repeatedly making "songs" of four notes duration lasting about two minutes each, reminiscent of the well-known Humpback Whale songs. Researchers believe that as this phenomenon has not been seen in any other populations, it may be unique to the B. m. brevicauda (Pygmy) subspecies. The reason for vocalization is unknown. Richardson et al (1995) discuss six possible reasons:[16]

  1. Maintenance of inter-individual distance
  2. Species and individual recognition,
  3. Contextual information transmission (e.g., feeding, alarm, courtship)
  4. Maintenance of social organization (e.g., contact calls between females and males)
  5. Location of topographic features
  6. Location of prey resources

Population and whaling

Hunting era

Main article: History of whaling
Blue whale populations have declined dramatically due to commercial whaling.

Blue Whales are not easy to catch or kill. Their speed and power meant that they were rarely pursued by early whalers who instead targeted Sperm and Right Whales.[17] In 1864 the Norwegian Svend Foyn equipped a steamboat with harpoons specifically designed for catching large whales.[18] Although initially cumbersome and with a low success rate, Foyn perfected the harpoon gun and soon several whaling stations had been established on the coast of Finnmark in northern Norway. Because of disputes with the local fisherman, the last whaling station in Finnmark was closed down in 1904.

Soon blue whales were being hunted in Iceland (1883), the Faroe Islands (1894), Newfoundland (1898), and Spitsbergen (1903). In 1904-05 the first blue whales were taken off South Georgia. By 1925, with the advent of the stern slipway in factory ships, and the use of steam-driven whale catchers, the catch of blue whales, and baleen whales as a whole, in the Antarctic and sub-Antarctic began to increase dramatically. Between 1930 and 1931, these ships killed 29,400 Blue Whales in the Antarctic alone. By the end of World War II populations had been significantly depleted, and in 1946 the first quotas restricting international trade in whales were introduced, but they were ineffective because of the lack of differentiation between species. Rare species could be hunted on an equal footing with those found in relative abundance. Blue Whale hunting was banned in the 1960s by the International Whaling Commission,[19][20] and illegal whaling by the USSR finally halted in the 1970s,[21] by which time 330,000 Blue Whales had been killed in the Antarctic, 33,000 in the rest of the Southern Hemisphere, 8,200 in the North Pacific, and 7,000 in the North Atlantic. The largest original population, in the Antarctic, had been reduced to 0.15% of their initial numbers.[22]

Whale hunters had clearly driven the Blue Whale to near-extinction, but rather than taking smaller harvests over a longer period, whalers continued to deplete the population. In hindsight, had the whaling industry taken into account monitoring and regulation by marine biologists, more whales might have been commercially available, albeit over a longer time span. The population dynamics involved in harvesting long-lived mammals are quite different from those involved in harvesting shorter-lived fish. Due to longer rates of reproduction (gestation of more than a year) and smaller litter size (one or two calves), whale populations recover much more slowly than the populations of smaller animals, which tend to invest less time and resources in individual young.

Population and distribution today

A Blue Whale set against the backdrop of the Azores
Image of a Blue Whale's tail fluke with the Santa Barbara Channel Islands in the background. August 2007.

Since the introduction of the whaling ban, studies have failed to ascertain whether the global Blue Whale population is increasing or remaining stable. In the Antarctic, best estimates show a significant increase at 7.3% per year since the end of illegal Soviet Union whaling, but numbers remain at under 1% of their original levels.[22] It has also been suggested that Icelandic and Californian populations are increasing but these increases are not statistically significant. The total world population was estimated to be between 5,000 and 12,000 in 2002, although there are high levels of uncertainty in available estimates for many areas.[23] The Blue Whale remains listed as "endangered" on the IUCN Red List of threatened species as it has been since the list's inception. The largest known concentration, consisting of about 2,000 individuals, is the North-East Pacific population of the Northern Blue Whale (B. m. musculus) subspecies that ranges from Alaska to Costa Rica, but is most commonly seen from California in summer. Sometimes this population strays over to the North-West Pacific; infrequent sightings between Kamchatka and the northern tip of Japan have been recorded.

In the North Atlantic, two stocks of B. m. musculus are recognized. The first is found off Greenland, Newfoundland, Nova Scotia and the Gulf of Saint Lawrence. This group is estimated to total about 500. The second, more easterly group is spotted from the Açores in Spring to Iceland in July and August; it is presumed that the whales follow the Mid-Atlantic Ridge between the two volcanic islands. Beyond Iceland, Blue Whales have been spotted as far north as Spitsbergen and Jan Mayen though such sightings are rare. Scientists do not know where these whales spend their winters. The total North Atlantic population is estimated to be between 600 and 1500.

In the Southern Hemisphere, there appear to be two distinct subspecies, B. m. intermedia, the Southern Blue Whale and the little studied Pygmy Blue Whale, B. m. brevicauda, found in Indian Ocean waters. Recent abundance estimates for the Antarctic subspecies range from 1100[24] to 1700.[22] Research into the number of Pygmy Blues is on-going. Estimates from a 1996 survey were that 424 Pygmy Blue Whales were in a small area south of Madagascar alone,[25] thus it is likely that numbers in the entire Indian Ocean are in the thousands. If this is true, the global numbers would be much higher than estimates predict.[26]

A fourth subspecies, B. m. indica, was identified by Blyth in 1859 in the northern Indian Ocean, but difficulties in identifying distinguishing features for this subspecies lead to it being used a synonym for B. m. musculus. It is now thought it could be the same subspecies as the Pygmy Blue Whale. Records for Soviet catches seem to indicate that the female adult size is closer to that of the Pygmy Blue than B. m. musculus, although the populations of B. m. indica and B. m. brevicauda appear to be discrete and the breeding seasons differ by almost six months.[27]

Migratory patterns of these subspecies are not well known. For example, Pygmy Blue Whales have been recorded in the northern Indian Ocean (Oman, Maldives, Sri Lanka) where they may form a distinct resident population. In addition, the population of Blue Whales occurring off Chile and Peru may also be a distinct population. Some Antarctic blue whales approach the eastern South Atlantic coast in winter, and occasionally their vocalizations are heard off Peru, Western Australia, and in the northern Indian Ocean. In Chile, the Cetacean Conservation Center, with support from the Chilean Navy, is undertaking extensive research and conservation work on a recently discovered feeding aggregation of the species off the coast of Chiloe Island in an area named "Golfo del Corcovado" where actually, sometimes, can be seen close to the coast with 326 animals spotted in 2007 summer season.

Efforts to calculate the Blue Whale population more accurately are supported by marine mammologists at Duke University who maintain the OBIS-SEAMAP (Ocean Biogeographic Information System - Spatial Ecological Analysis of Megavertebrate Populations), a collation of marine mammal sighting data from around 130 sources.[28]

Threats other than hunting

Blue Whales may be wounded, sometimes fatally, after colliding with ocean vessels as well as becoming trapped or entangled in fishing gear.[29] The ever-increasing amount of ocean noise drowns out the vocalizations produced by whales, which may make it harder for whales to communicate.[29] Human threats to the potential recovery of Blue Whale populations also include accumulation of polychlorinated biphenyl (PCB) chemicals within the whale's body.

With global warming causing glaciers and permafrost to rapidly melt and allowing a large amount of fresh water to flow into the oceans, there are concerns that if the amount of fresh water in the oceans reaches a critical point there will be a disruption in the thermohaline circulation. Considering the Blue Whale's migratory patterns are based on ocean temperature, a disruption in this circulation which moves warm and cold water around the world would be likely to have an effect on their migration.[30] The whales summer in the cool, high latitudes, where they feed in krill-abundant waters; they winter in warmer, low latitudes, where they mate and give birth.[31]

The change in ocean temperature would also affect the Blue Whale’s food supply. The warming trend and decreased salinity levels would cause a significant shift in krill location and abundance.[32]

Blue Whale skeleton, outside the Long Marine Laboratory at the University of California, Santa Cruz

The Natural History Museum in London contains a famous mounted skeleton and life-size model of a Blue Whale, which were both the first of their kind in the world, but has since been replicated at the University of California, Santa Cruz. Similarly, the American Museum of Natural History in New York City has a full-size model in its Milstein Family Hall of Ocean Life. Living Blue Whales may be encountered on whale-watching cruises in the Gulf of Maine,[33] and are the main attractions along the north shore of the Gulf of Saint Lawrence and in the Saint Lawrence estuary.[29] The Blue Whale has been represented in children's popular culture in the 1967 movie Doctor Dolittle, where it appears as a symbol of size and strength when it is employed to move an island.

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Notes

  1. ^ Sears R, Wenzel FW, Williamson JM (1987). "The Blue Whale: A Catalogue of Individuals from the Western North Atlantic (Gulf of St. Lawrence)". Mingan Island Cetacean Study, St. Lambert, Quebec.: 27.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ Sears, R (1990). "The Cortez blues". Whalewatcher. 24 (2): 12–15.
  3. ^ Kawamura, A (1980). "A review of food of balaenopterid whales". Sci. Rep. Whales Res. Inst. 32: 155–197.
  4. ^ Yochem PK, Leatherwood S (1980). "Blue whale Balaenoptera musculus (Linnaeus, 1758)". In Ridgway SH, Harrison R (ed.). Handbook of Marine Mammals, Vol. 3:The Sirenians and Baleen Whales. London: Academic Press. pp. 193–240.
  5. ^ Cite error: The named reference afsc was invoked but never defined (see the help page).
  6. ^ Nemoto T (1957). "Foods of baleen whales in the northern Pacific". Sci. Rep. Whales Res. Inst. 12: 33–89.
  7. ^ Nemoto T, Kawamura A (1977). "Characteristics of food habits and distribution of baleen whales with special reference to the abundance of North Pacific sei and Bryde's whales". Rep. int. Whal. Commn. 1 (Special Issue): 80–87.
  8. ^ a b c "Blue Whale - ArticleWorld". {{cite web}}: Unknown parameter |accessmonthdate= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  9. ^ a b Cite error: The named reference SearsCal02 was invoked but never defined (see the help page).
  10. ^ "www.npca.org". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  11. ^ J. Calambokidis, G. H. Steiger, J. C. Cubbage, K. C. Balcomb, C. Ewald, S. Kruse, R. Wells and R. Sears (1990). "Sightings and movements of blue whales off central California from 1986–88 from photo-identification of individuals". Rep. Whal. Comm. 12: 343–348.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ William Perrin and Joseph Geraci. "Stranding" pp 1192–1197 in Encyclopedia of Marine Mammals (Perrin, Wursig and Thewissen eds)
  13. ^ "The Whale bone Arch". Places to Visit around the Isle of Lewis. {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  14. ^ W.C. Cummings and P.O. Thompson (1971). "Underwater sounds from the blue whale Balaenoptera musculus". Journal of the Acoustics Society of America. 50(4): 1193–1198.
  15. ^ W.J. Richardson, C.R. Greene, C.I. Malme and D.H. Thomson (1995). Marine mammals and noise. Academic Press, Inc., San Diego, CA. ISBN 0-12-588441-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
  16. ^ National Marine Fisheries Service (2002). "Endangered Species Act - Section 7 Consultation Biological Opinion" (PDF).
  17. ^ Scammon CM (1874). The marine mammals of the northwestern coast of North America. Together with an account of the American whale-fishery. San Francisco: John H. Carmany and Co. p. 319.
  18. ^ Cite error: The named reference factsheet was invoked but never defined (see the help page).
  19. ^ Gambell, R (1979). "The blue whale". Biologist. 26: 209–215.
  20. ^ Best, PB (1993). "Increase rates in severely depleted stocks of baleen whales". ICES J. mar. Sci. 50: 169–186. {{cite journal}}: Cite has empty unknown parameter: |month= (help)
  21. ^ Yablokov, AV (1994). "Validity of whaling data". Nature. 367: 108.
  22. ^ a b c Cite error: The named reference Ant was invoked but never defined (see the help page).
  23. ^ Cite error: The named reference pop was invoked but never defined (see the help page).
  24. ^ T.A. Branch, D.S. Butterworth (2001). "Estimates of abundance south of 60°S for cetacean species sighted frequently on the 1978/79 to 1997/98 IWC/IDCR-SOWER sighting surveys". Journal of Cetacean Research and Management. 3: 251–270. {{cite journal}}: line feed character in |title= at position 58 (help)
  25. ^ P.B. Best; et al. (2003). "The abundance of blue whales on the Madagascar Plateau, December 1996". Journal of Cetacean Research and Management. 5: 253–260. {{cite journal}}: Explicit use of et al. in: |author= (help)
  26. ^ Cite error: The named reference BBC_pop was invoked but never defined (see the help page).
  27. ^ T. A. Branch, K. M. Stafford; et al. (2007). "Past and present distribution, densities and movements of blue whales in the Southern Hemisphere and adjacent waters" (PDF). International Whaling Commission. {{cite web}}: Explicit use of et al. in: |author= (help); Unknown parameter |accessdaymonth= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  28. ^ The data for the Blue Whale, along with a species profile, may be found here
  29. ^ a b c Reeves RR, Clapham PJ, Brownell RL, Silber GK (1998), Recovery plan for the blue whale (Balaenoptera musculus) (PDF), Silver Spring, MD: National Marine Fisheries Service, p. 42, retrieved 2007-06-20{{citation}}: CS1 maint: multiple names: authors list (link)
  30. ^ Robert A. Robinson, Jennifer A. Learmonth, Anthony M. Hutson, Colin D. Macleod, Tim H. Sparks, David I. Leech, Graham J. Pierce, Mark M. Rehfisch and Humphrey Q.P. Crick (August 2005). "Climate Change and Migratory Species" (PDF). BTO. {{cite web}}: Unknown parameter |accessdaymonth= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)CS1 maint: multiple names: authors list (link)
  31. ^ Hucke-Gaete, Rodrigo, Layla P. Osman, Carlos A. Moreno, Ken P. Findlay, and Don K. Ljungblad (2003). "Discovery of a Blue Whale Feeding and Nursing Ground in Southern Chile". The Royal Society: s170–s173.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  32. ^ Moline, Mark A., Herve Claustre, Thomas K. Frazer, Oscar Schofield, and Maria Vernet (2004). "Alteration of the Food Web Along the Antarctic Peninsula in Response to a Regional Warming Trend". Global Change Biology. 10: 1973–1980.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  33. ^ Wenzel FW, Mattila DK, Clapham PJ (1988). "Balaenoptera musculus in the Gulf of Maine". Mar. Mammal Sci. 4: 172–175.{{cite journal}}: CS1 maint: multiple names: authors list (link)

References

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