Sei Whale

From Encyclopedia Jr, free information reference for Kids

Sei Whale
A Sei Whale surfacing side-on Size comparison against an average human
Conservation status
Endangered (EN)[1]
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Subclass: Eutheria Order: Cetacea Suborder: Mysticeti Family: Balaenoptiidae Genus: Balaenoptera Species: B. borealis
Binomial name
Balaenoptera borealis Lesson, 1828
Sei Whale range

The Sei Whale (pronounced: [seɪ] or [saɪ]), Balaenoptera borealis, is a baleen whale, the third largest member of the Balaenopteridae family after the Blue Whale and the Fin Whale.^[2] Other related whales from the same family include the Humpback Whale, the Bryde's Whale, and the Minke Whale. Its name comes from the Norwegian word for pollock, a fish that appears off the coast of Norway at the same time as the Sei Whale.^[3] The whale reaches lengths of 20 metres (66 ft) long and weights of up to 30,000 kilograms (66,000 lb).^[4] It eats an average of about 900 kilograms (2,000 lb) of food each day, primarily marine copepods and krill.^[5] It is among the fastest of all cetaceans, and can reach speeds of up to 50 kilometres per hour (31 mi/hr, 27 knots) over short distances.^[5]

The Sei Whale can be found worldwide in a band stretching from about 60 degrees south latitude to 60 degrees north latitude, preferring deep off-shore waters^[6] and tending to avoid tropical waters and semi-enclosed bodies of water such as the Gulf of Mexico, the Gulf of St. Lawrence, Hudson Bay, the North Sea, and the Mediterranean Sea. In general, the Sei Whale migrates annually from cool and subpolar waters in summer to temperate and tropical waters for winter, although in some areas the exact migration routes are not known.^[4]

Following large-scale commercial hunting of the species between the late-nineteenth and late-twentieth centuries when over 238,000 individuals were caught,^[7] the Sei Whale is now an internationally protected species,^[1] although it continues to be hunted to a limited extent under controversial scientific research programmes conducted by Iceland and Japan.^[8] Today, the worldwide population of the Sei Whale is about 54,000, approximately one-fifth of its pre-whaling population.^[3]

Contents 1 Taxonomy and naming 2 Physical description and behaviour 2.1 Feeding 2.2 Life history 3 Habitat and migration 4 Whaling 4.1 North Atlantic 4.2 North Pacific 4.3 Southern Hemisphere 4.4 International protection 4.5 Current whaling 5 Historic and current abundance 6 See also 7 References 7.1 General References 8 External links

[edit] Taxonomy and naming

The species was first described by René-Primevère Lesson in 1828, but a further description was given by Karl Asmund Rudolphi and the species is often referred to as Rudolphi's Rorqual in older texts.^[9] Other common names for the species include the Pollack Whale and Coalfish Whale.

Sei Whales are rorquals (family Balaenopteridae), a family that includes the Humpback Whale, the Blue Whale, Bryde's Whale, the Fin Whale and the Minke Whale. The family Balaenopteridae is believed to have diverged from the other families of the suborder Mysticeti as long ago as the middle Miocene.^[10] However, it is not known when the members of these families diverged from each other.

The word Sei comes from the Norwegian word seje for pollock, a close relative of codfish. Sei Whales appeared off the coast of Norway at the same time as the pollock, both coming to feed on the abundant plankton.^[3] Two geographically separated subspecies have been identified - the Northern Sei Whale (B. b. borealis) and Southern Sei Whale (B. b. schleglii).^[11]

[edit] Physical description and behaviour

The Sei Whale is the third largest member of the Balaenopteridae family, after the Blue Whale and the Fin Whale.^[2] Mature adults typically measure between 12.2 and 15.2 metres (40–50 ft)^[5] and weigh 20,000 to 30,000 kilograms (44,000–66,000 lb). The Southern Sei Whale is larger than the Northern Sei Whale, and females are considerably larger than males.^[4] The largest known Sei Whale measured 20 metres (66 ft),^[5] and weighed between 40,000 and 45,000 kilograms (88,000–100,000 lb). The largest specimens taken off Iceland were slightly longer than 16 metres (52 ft).^[12] At birth, a calf typically measures 4–5 metres (13–16 ft) in length.^[5] The Sei Whale is among the fastest of all cetaceans, and can reach speeds of up to 50 kilometres per hour (31 mi/hr, 27 knots) over short distances.^[5]

The whale's body is typically a dark steel grey with irregular light grey to white markings on the ventral surface. The whale has a series of 32-60 pleats or grooves along the bottom of the body that allow the throat area to expand greatly during feeding. It has a sickle-shaped dorsal fin that ranges in height from 25 to 61 centimetres (10 to 24 in). The snout is pointed and the pectoral fins are short.^[5] It has single ridge extending from the tip of the snout to the paired blowholes. The whale's skin is often marked by pits or wounds, which after healing become white scars. These are believed to be caused by ectoparisitic copepods (Penella spp.),^[13] lampreys,^[14] or possibly "cookie-cutter" sharks (Isistius brasiliensis).^[15] The dorsal fin is usually prominent and back-curved, set about two-thirds of the way back from the tip of the snout. Dorsal fin shape, pigmentation pattern, and scarring have been used to a limited extent in photo-identification studies of Sei Whales.^[16] The tail is thick and the fluke is small in relation to body size.

This rorqual is a filter feeder, using its baleen to obtain its food from the water by opening its mouth, engulfing large amounts of water, then straining it out through its baleen plates, trapping any food items inside the mouth. An adult has between 300 and 380 ashy-black baleen plates on each side of the mouth, about 48 centimetres (19 in) long. Each plate is made of fingernail-like keratin that frays out into whitish fine hairs on the ends inside the mouth near the tongue.^[5] The very fine bristles of the Sei Whale's baleen (about 0.1 mm, .004 in) are cited as the most reliable feature distinguishing it from all other baleen whales.^[17]

The Sei Whale looks similar to other large baleen whales. The best way to distinguish between it and the Bryde's Whale, apart from differences in each whale's baleen, is by the presense of lateral ridges on the dorsal surface of the Bryde's Whale's head. Large Sei Whales can be confused with Fin Whales unless the Fin Whale's asymmetrical head colouration is clearly seen; the right side of the lower jaw of the Fin Whale is white, and the left side is grey. Viewed from the side, the Sei Whale's head has a slight arch that differs from the comparatively flat profile of the Fin Whale.^[4]

Sei Whales usually move alone^[18] or in small groups of up to six individuals.^[16] Larger groups have been seen at particularly abudant feeding grounds. They appear to not have any well-defined social structure.^[2]

The whale's dive sequence is more regular than its close relatives. Blows occur at intervals of about 40 to 60 seconds for a few minutes followed by a "deep dive" lasting five to fifteen minutes. Between shallow dives the whale stays close to the surface and remains visible in clear, calm waters. Unlike the Fin Whale, the Sei Whale tends not to roll high out of the water as it dives. The blowholes and dorsal fin are often exposed above the water surface simultaneously. The whale almost never extends its flukes above the surface, and it rarely breaches.^[4]

[edit] Feeding

The whale feeds near the surface of the ocean, swimming on its side through swarms of prey. An average Sei Whale eats about 900 kilograms (2,000 lb) of food each day.^[5] In the North Atlantic, the Sei Whale feeds primarily on calanoid copepods, with a secondary preference for euphausiids.^[19] Its preference for zooplankton has been determined from stomach analyses, direct observations of feeding behaviour, and examination of feces collected near Sei Whales.^[20][21] It competes for food with a variety of other species, including clupeid fishes, basking sharks, and Right Whales. In the North Pacific, the Sei Whale feeds on similar zooplankton, in addition to larger organisms, including pelagic squid and fish the size of adult mackerel.^[22] Some fish in its diet are commercially important. Off central California, it feeds on anchovies from June through August, and on krill (Euphausia pacifica) during September and October.^[14]

[edit] Life history

Mating occurs in temperate, low-latitude seas during the winter, and the gestation period is estimated to be 10 3/4 months,^[23] 11 1/4 months,^[24] or one year,^[25] depending on what model of fetal growth is used. A newborn weans from its mother at 6 or 9 months of age when it is 11 or 12 metres (36 to 39 ft) in length,^[23] so weaning takes place on the feeding grounds in summer or autumn. Females reproduce every 2 to 3 years,^[23] with as many as 6 foetuses being reported, but single births are far more common.^[5] The average age of sexual maturity of both sexes is 8 to 10 years,^[23] at a length of around 12 metres (40 ft). for males and 13 metres (50 ft) for females.^[3]

[edit] Habitat and migration

Sei Whales are found worldwide in a band stretching from about 60 degrees south latitude to 60 degrees north latitude, preferring deep off-shore waters^[6] and tending to avoid tropical waters.^[4] The difficulty of distinguishing Sei Whales at seas from their close relatives, Bryde's Whales and in some cases from Fin Whales, has created confusion about their distributional limits and frequency of occurance, especially in warmer waters where Bryde's Whales are most common.

In the North Atlantic, the range of the Sei Whale extends from southern Europe or northwestern Africa to Norway in the east, and from the southern United States to West Greenland in the west.^[6] The southernmost confirmed records are strandings along the northern Gulf of Mexico and in the Greater Antilles.^[17] Throughout its range, the whale tends to avoid semi-enclosed bodies of water such as the Gulf of Mexico, the Gulf of St. Lawrence, Hudson Bay, the North Sea, and the Mediterranean Sea.^[4] It occurs predominantly in deep water, occuring most commonly over the continental slope,^[26] in basins situated between banks,^[27] or submarine canyon areas.^[28]

In the North Pacific, the Sei Whale is found from 20°N to 23°N latitude in the winter, and from 35°N to 50°N latitude in the summer.^[29] Approximately 75% of the total population of Sei Whales in the North Pacific is found east of longitude 180°W,^[7] but there is a significant lack of information regarding the overall distribution of the whales in the North Pacific. Two whales tagged off California were later captured off Washington and British Columbia, revealing a possible link between these areas,^[30] but the lack of other tag recovery data makes these two cases inconclusive. In the Southern Hemisphere, summer distribution based upon historic catch data is between 40°S to 50°S latitude, while winter distribution is unknown.^[31]

In general, the Sei Whale migrates annually from cool and subpolar waters in summer to temperate and tropical waters for winter.^[4] In the northwest Atlantic, sightings and catch records suggest that the whale moves north along the shelf edge to arrive in the areas of Georges Bank, Northeast Channel, and Browns Bank by mid to late June. They are present off the south coast of Newfoundland in August and September, and a southbound migration begins moving west and south along the Nova Scotian shelf from mid-September to mid-November. Whales in the Labrador Sea as early as the first week of June may move farther northward to waters southwest of Greenland later in the summer.^[32] In the northeast Atlantic, the Sei Whale winters as far south as West Africa and follows the continential slope northward in spring. Large females lead the northward migration and reach the Denmark Strait earlier and more reliably than other sexes and classes, arriving in mid-July and remaining through mid-September. In some years, males and younger females remain at lower latitudes during the summer months.^[12]

Despite knowing some general trends in the migration pattern of the Sei Whale, exact migration routes are not known^[12] and it is not easy to predict exactly where groups will appear from one year to the next. A particular location may one year see an influx of many whales only for them not to return for several years afterwards.^[33] F.O. Kapel noted a correlation between the ocassional appearance of the Sei Whale and the incursions of relatively warm waters off the Irminger Current off West Greenland.^[34] Some evidence from tagging data indicates that individual Sei Whales return off the coast of Iceland on an annual basis.^[35]

[edit] Whaling

Main articles: Whaling and History of whaling

The development of explosive harpoons and steam-powered catcher boats in the late nineteenth century allowed the exploitation of previously unobtainable large whales by commercial whalers. Because of their quick speed and elusiveness,^[36] and later because of their comparatively small yield of oil and meat, the Sei Whale was initially not generally hunted while sufficient stocks of Right Whales, Blue Whales, Fin Whales, and Humpback Whales were available. As these stocks became depleted, Sei Whales were hunted in earnest, particularly in the 1950s through the 1970s.^[2]

[edit] North Atlantic

In the North Atlantic, Sei Whales were hunted in large numbers off the coast of Norway and Scotland beginning in the late nineteenth and twentieth centuries.^[33] In 1885 alone, more than 700 Sei Whales were killed off Finnmark, Norway.^[37] Sei Whale meat was a popular food in Norway, and it was the value of the meat that made the hunting of this difficult-to-catch species economically feasible in the early twentieth century.^[38] Small numbers of Sei Whales were taken off Spain, Portugal, and in the Strait of Gibraltar beginning in the 1920s,^[39] and by Norwegian and Danish whalers off West Greenland from the 1920s to the 1950s.^[34] In Iceland, a total of 2,574 whales were taken from the Hvalfjörður whaling station between 1948 and 1985. Since the late 1960s or early 1970s, the Sei Whale has been second only to the Fin Whale as a preferred target of Icelandic whalers, with the demand for high-quality meat taking precedence over that for whale oil.^[36] A total of 825 Sei Whales were taken off the Nova Scotian shelf by whalers operating out of Blandford, Nova Scotia between 1966 and 1972.^[32] Overall, 14,295 Sei Whales were captured in the North Atlantic Ocean between 1885 and 1984.^[7]

[edit] North Pacific

In the North Pacific, the total reported kill of Sei Whales by commercial whalers was 72,215 between 1910 and 1975,^[7] and 61,500 between 1947 and 1987.^[40] At shore stations in Japan and Korea, 300 to 600 Sei Whales were taken each year by whalers between 1911 and 1955. In 1959, the Japanese catch peaked when 1,340 whales were caught. Heavy exploitation by pelagic whalers in the North Pacific began in the early 1960s, with total catches averaging 3,643 per year from 1963 to 1974 (total 43,719; annual range 1,280 to 6,053).^[41] In 1971, after a decade of high Sei Whale catch numbers, the species became scarce in Japanese waters.^[42][31] Off the coast of North America, Sei Whales were hunted by Canadians in British Columbia from the late 1950s to the mid 1960s, when the number of whales captured dropped to around 14 per year.^[2] More than 2,000 were killed in British Columbia waters between 1962 and 1967.^[43] Between 1957 and 1971, California shore whalers captured 386 whales.^[14] Commercial whaling for Sei Whales ended in the western North Pacific in 1975, and in the eastern North Pacific in 1971.

[edit] Southern Hemisphere

A total of 152,233 Sei Whales were caught in the Southern Hemisphere between 1910 and 1979.^[7] Whaling in the southern oceans originally targeted Humpback Whales. By 1913, this target species became rare and the catch of Fin and Blue Whales began to increase. As these species likewise became scarce, Sei Whale catches increased rapidly in the late 1950s and early 1960s.^[31] The catch peaked in 1964 at over 20,000 Sei Whales, but by 1976, this number had dropped to below 2,000 and commercial whaling for the species ended in 1977.^[2]

[edit] International protection

The Sei Whale did not have meaningful protection at the international level until 1970, when catch quotas for the North Pacific began to be set on a species basis by the International Whaling Commission (IWC). Prior to that time, the kill was limited only by whalers' ability to find the whales.^[44] The Sei Whale was given complete protection from commercial whaling in the North Pacific in 1976, and quotas on Sei Whales were introduced in the North Atlantic in 1977. With the moratorium on commercial whaling taking effect in the Northern Hemisphere in 1986, all legal whaling for Sei Whales stopped.^[4] In the late 1970's, some "pirate" whaling took place in the eastern North Atlantic.^[45] There is no direct evidence of illegal whaling in the North Pacific, although the acknowledged misreporting of whaling data by the Soviet Union^[46] means that catch data are not entirely reliable. The species remained listed on the IUCN Red List of Threatened Species in 2000, categorised as "endangered".^[1] Populations in the Southern Hemisphere are listed as CITES Appendix I, indicating that they are threatened with extinction if trade is not halted. Populations in the Northern Hemisphere are listed as CITES Appendix II, indicating that they are not necessarily threatened with extinction, but may become so if they are not listed.^[5]

[edit] Current whaling

Since the moratorium on commercial whaling, some Sei Whales have been caught and killed by Icelandic and Japanese whalers under the IWC's scientific research programme. Iceland carried out four years of scientific whaling between 1986 and 1989, catching up to 40 Sei Whales a year.^[47] Japanese scientists kill approximately 50 Sei Whales each year for this purpose. The main focus of the research is to examine what Sei Whales eat and to determine the level of competition between whales and fisheries. Dr. Seiji Ohsumi, Director General of the Institute of Cetacean Research in Tokyo, said "It is estimated that whales consume 3 to 5 times the amount of marine resources as are caught for human consumption, so our whale research is providing valuable information required for improving the management of all our marine resources."^[48] He later added that "...Sei Whales are the second most abundant species of whale in the western North Pacific, with an estimated population of over 28,000 animals. [It is] clearly not endangered."^[49] Environmental campaigners dispute the necessity of the research, saying that it is known that Sei Whales feed primarily on squid and plankton not hunted by humans, and only rarely on fish. They claim that the programme is "nothing more than a plan designed to keep the whaling fleet in business, and the need to use whales as the scapegoat for over-fishing by humans."^[8] The scientific quality of the research itself has been criticised as being very poor; at the 2001 meeting of the IWC Scientific Committee, 32 scientists submitted a document expressing their belief that the Japanese programme lacked scientific rigour and would not meet minimum standards of academic review that are widely used in science world-wide.^[50]

[edit] Historic and current abundance

The global population of the Sei Whale is estimated at only 54,000, about one fifth of the population before the era of commercial whaling.^[3] In the North Atlantic, the most current (1991) estimate based upon the history of catches and catch per unit effort (CPUE) data is 4,000.^[51] This low-precision estimate is not considered a true scientific index of abundance.^[52] Sei Whales were said to have been scarce in the 1960's and early 1970's off northern Norway, where plentiful numbers were taken at the end of the nineteenth century through the Second World War.^[53] One possible explanation for this dissapearance is that the whales were overexploited,^[53] while an alternative explanation is that a drastic reduction in copepod stocks in the northeastern Atlantic during the late 1960's caused a change in Sei Whale distribution.^[54] Surveys in the Denmark Strait found 1,290 whales in 1987, and 1,590 whales in 1989.^[54] Population levels off Nova Scotia are estimated to be between 1,393 and 2,248, with a minimum estimate of 870.^[32]

The most current (1977) population estimate for the Pacific Ocean is 9,110, based upon the history of catches and CPUE data.^[41] This figure is disputed by Japanese whaling interests, who in 2002 claimed that the population of Sei Whales in the western North Pacific was over 28,000 whales,^[49] but this figure has not been accepted by the scientific community.^[8] In California waters, there was only one confirmed and five possible sightings from 1991,^[55][56] 1992,^[56] and 1993^[57] aerial and ship surveys, and there were no confirmed sightings off Oregon and Washington aerial surveys. Prior to commercial whaling activities, there were an estimated 42,000 Sei Whales in the North Pacific.^[41] By the end of the period of exploitation (1974), there numbers had been reduced to between 7,260 and 12,620.^[41]

In the Southern Hemisphere, current Sei Whale abundance estimates range between 9,800 and 12,000 whales, based upon the history of catches and CPUE in the southern oceans.^[51] The IWC reported an estimate of 9,718 whales based upon survey data between 1978 and 1988.^[58] Prior to commercial whaling, there were an estimated 65,000 Sei Whales living in the Southern Hemisphere.^[51]

[edit] See also

• Whaling
• International Whaling Commission
• Whaling in Japan
• Whaling in Iceland

[edit] References

[edit] General References

[edit] External links

• ARKive - images and movies of the sei whale (Balaenoptera borealis)
• News report on Japanese whalers hunting Sei Whales in 2002/2003