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The Sei Whale The Great Whales: History and Status of Six Species Listed as Endangered Under the U.S. Endangered Species Act of 1973 Item Type article Authors Perry , Simona L.; DeMaster, Douglas P.; Silber , Gregory K. Download date 24/09/2021 08:16:12 Link to Item http://hdl.handle.net/1834/26411 The Sei Whale Introduction balaenopterids, sei whales appear re- North Atlantic stricted to the more temperate waters The sei whale, Balaenoptera borea- and occur within a smaller range of lati- The IWC recognizes three sei whale lis Lesson 1828, is the third largest tudes (Mizroch et al., 1984c). They do stocks in the North Atlantic (Fig. 32): member of the family Balaenopteridae, not associate with coastal features, but following the blue, B. musculus; and fin, instead they are found in deeper waters 1) Nova Scotia, B. physalus, whales. At maturity, sei associated with the continental shelf 2) Iceland-Denmark Strait, and whales range from 12 to 18 m in length edge (Hain et al., 1985). There is some 3) Northeast Atlantic. (Lockyer, 1977; Martin, 1983). Their evidence from catch data of differen- coloration is gray, with a variable white tial migration patterns by reproductive However, the IWC noted that identi- region from the chin to the umbilicus. class, whereby females arrive at and fication of sei whale stocks is very dif- The undersides and sides of the whale depart from feeding areas earlier than ficult, and that these three stocks are may appear mottled, with gray or white males (Matthews, 1938; Gambell, based on regions of past whaling op- circular scars caused by ectoparasitic 1968). erations, as opposed to biological infor- copepods, Penella spp. (Andrews, 1916; mation (Donovan, 1991). Mitchell and North Pacific Ivashin and Golubovsky, 1978), lam- Chapman (1977) noted another possible preys (Pike, 1951; Rice, 1977a), or The IWC’s Scientific Committee has stock boundary separating the Nova cookiecutter sharks, Isistius brasiliensis designated the entire North Pacific Scotia stock from sei whales off north- (Shevchenko, 1977). The dorsal fin is Ocean as one sei whale stock unit east Newfoundland and Labrador based generally tall, slender, and—compared (Donovan, 1991). However, mark-re- on catch data, tag recoveries, and known to the blue and fin whale—further for- capture studies using Discovery tag38 migration patterns. In the northwest ward on the body (Fig. 30). and catch distribution data, as well as Atlantic, whales travel along the east- The sei whale is usually found alone comparisons of morphology, indicate ern Canadian coast in autumn, June, and or in small groups, and the species ap- that more than one stock exists: one July on their way to and from the Gulf pears to have no well-defined social between long. 175°W and 155°W and of Maine and Georges Bank, where they structure. Like other balaenopterids, another east of long. 155°W (Fig. 4, 5) occur in winter and spring (Mitchell, they have fringed baleen plates instead (Masaki, 1976, 1977). During winter, 1975b; Blaylock et al., 1995). Peak of teeth and ventral grooves which ex- sei whales are found from lat. 20° to abundance in U.S. waters occurs in pand to allow for engulfing large quan- 23°N and during the summer from lat. spring along eastern Georges Bank, into tities of water during feeding on small 35° to 50°N (Masaki, 1976, 1977). the Northeast Channel, and along the zooplankton. Mead (1977) noted that Horwood (1987) reported that 75–85% southwest edge of Georges Bank in the sei whale baleen is much finer than that of the total North Pacific population of area of Hydrographer Canyon (CeTAP70). of other Balaenoptera species and is a sei whales resides east of long. 180°W. In years of copepod abundance, more reliable feature for species identification. Within the U.S.EEZ69 there is a sig- whales are found inshore of these ar- nificant lack of information regarding eas, such as in the Great South Chan- Distribution and Migration the distribution of sei whales in the east- nel, on Stellwagen Bank, and in the Gulf Sei whales are found in all oceans ern North Pacific (Barlow et al., 1997). of Maine (Payne et al., 1990; Schilling (Fig. 31). These whales migrate long Two whales tagged off California were et al., 1992). distances from high-latitude summer later captured off Washington and Brit- In the northeast Atlantic, sei whales feeding areas to relatively low-latitude ish Columbia, revealing a possible link winter south of Spain, move to the winter breeding areas. For the most part, between these two areas (Rice, 1974). Spanish, Portuguese, and western Ire- the location of these winter areas re- However, the lack of other tag recovery land coasts in early spring, to the north- mains a mystery. Compared to other data makes these two cases inconclusive. west of the Shetland Islands, off the 52 Marine Fisheries Review 61(1), 1999 Figure 30.—Underwater views of a sei whale. G. Williamson, NMML Collection. 53 Figure 31.—Worldwide sei whale distribution. Adapted from Mizroch et al. (1984c). Hebrides, and west Norway in April through May, and summer off north Norway, west Norway, the Shetland Is- lands, the Hebrides, and the Faeroe Is- lands (Fig. 7) (Ingebrigtsen, 1929). Occasionally, sei whales are found as far north as Bear Island and Spitsbergen (about lat. 72°N) (Fig. 18) (Jonsgård, 1966). Southern Hemisphere The IWC recognizes six sei whale stock areas in the Southern Ocean (Fig. 9) (Donovan, 1991). In general, Antarc- tic austral summer distribution based on historic catch data is from lat. 40° to 50°S, while austral winter distribution is unknown (Mizroch et al., 1984c; Anonymous, 1994b). There is no con- clusive evidence of potential wintering areas for any of these stocks, although Discovery tag38 data from captured whales showed links between some re- gions (IWC, 1977). For instance, links were found between the Brazilian coast with the western half of Area II, the Figure 32.—North Atlantic sei whale stock boundaries recognized by the IWC Natal Coast of South Africa with the (Donovan, 1991). eastern half of Area III and with the 54 Marine Fisheries Review western half of Area IV, and western and No sei whales were sighted during a more from 1911 to 1955. The Japanese sei southeastern Australia with Area IV. recent (August through October 1991) whale catch peaked in 1959, when 1,340 aerial survey conducted during the whales were caught. In 1971, after a de- Current and Historical Abundance CeTAP study. cade of high sei whale catch numbers, this There is no information on the initial species became scarce in Japanese waters. North Pacific abundance of sei whales in the North After 1975, sei whales became protected The most current (1977) population Atlantic prior to commercial whaling. in the western North Pacific under IWC estimate for the North Pacific Ocean is But, in 1966, there were an estimated authority (Mizroch et al., 1984c). 9,110 (no CV) based on the history of 1,856 whales in the Nova Scotia stock Off the west coast of North America, catches and trends in CPUE22 (Tillman, and 828 whales in the Labrador Sea sei whales were commercially hunted 1977; Braham3). There are no estimates (Mitchell, 1974a). by Canadians in British Columbia from of abundance for this ocean based on the late 1950’s until the mid 1960’s, Southern Hemisphere aerial or ship sighting surveys. In Cali- when the number of whales captured fornia waters, there were only one con- Based on the history of catches and dropped to around 14 individuals per firmed and five possible sei whale trends in CPUE22, current sei whale year. Along the U.S. coast, shore-based sightings from 1991, 1992, and 1993 abundance estimates range from 9,800 whaling operations existed in Califor- aerial and ship surveys (Hill and to 12,000 whales in the Southern nia (Cherfas, 1989). After 1971, hunt- Barlow, 1992; Carretta and Forney, Oceans (IWC, 1980b; Mizroch et al., ing of sei whales ceased in the eastern 1993; Mangels and Gerrodette, 1994). 1984c; Braham3). The IWC reported an North Pacific. There were no confirmed sightings off estimate of 9,718 whales (no CV) based North Atlantic Washington and Oregon during recent on results of the 1978 through 1988 JSV aerial surveys (Green et al.75). and IWC/IDCR survey data (IWC, From 1885 through 1984, approxi- Prior to commercial whaling in the 1996a). mately 14,295 sei whales were taken in North Pacific (late 1800’s to early Braham3 estimated that 65,000 sei the North Atlantic Ocean (Horwood, 1900’s), there were an estimated 42,000 whales occurred in the Southern Hemi- 1987). These whales were first hunted sei whales (Tillman, 1977). By the end sphere prior to commercial whaling. off Norway during the late 1800’s, of the period of exploitation (1974), Similarly, the IWC used catch data from where they became the target species their numbers had been reduced to be- the 1930’s to estimate that 63,100 sei in late summer, after the blue and fin tween 7,260 and 12,620 (no CV) whales occurred prior to commercial whales had already migrated out of high (Tillman, 1977). whaling in the Southern Oceans (IWC, latitude North Atlantic waters. And, as 1980b; Mizroch et al., 1984c). the stocks of blue and fin whales be- North Atlantic came scarce, sei whale catches gained Historic Exploitation Patterns The most current (1991) population importance in this region (Mizroch et al., estimate for the entire North Atlantic In 1864, explosive harpoons and 1984c). Sei whales were originally hunted Ocean based on the history of catches steam-powered catcher boats were in- only off Norway and Iceland, but from and trends in CPUE22 is 4,000 (no CV) troduced in Norway, allowing the large- 1967 through 1972, sei whales were also (Braham3).
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