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Home , Fin whale, Sei whale

The Sei , borealis

SALLY A. MIZROCH, DALE W. RICE, and JEFFREY M. BREIWICK

Introduction balaenopterids have fringed from high- summer feeding plates instead of teeth, and feed on grounds to lower latitude winter areas The , Balaenoptera swarms of small which (Fig. 1). Populations north and south borealis Lesson, 1828, can range in they capture in their baleen as water is of the are presumed to be length up to 18.5 m (60 feet), which filtered through. Sei , like other separate, as their migration schedules makes it the third largest whale in the baleen whales, do not have a well­ are 6 months out of phase. family Balaenopteridae, following the defined school or social structure, and Unlike most other balaenopterids, blue, B. musculus, and fin, B. are generally found in small groups or sei whales tend to be restricted to physalus, whales. Sei whales are gray as solitary individuals (Tomilin, more temperate waters, and conse­ with a variable white area extending 1957). quently are generally found within a from the to the umbilicus. All the smaller range of . Although Distribution and Migration The authors are with the National Marine there have been sporadic reports of sei Laboratory, Northwest and Alaska Like most balaenopterids, sei whales close to the ice edge, this is Fisheries Center, National Marine Fisheries thought to be uncommon (Jonsgllrd, Service, NOAA, 7600 Sand Point Way N.E., whales are found in all oceans and Bin CI5700, Seattle, WA 98115. migrate long distances north-south 1966).

Figure 1. -Geographical distribution of the sei whale. Simple hatching indicates the summer feeding grounds. Stippling indicates distribution during autumn, winter, and spring; records are scarce during these , and the distribution is to a large extent speculative.

46(4),1984 25 A sei whale surfacing in Antarctic waters, showing the tall, sickle-shaped characteristic of this species. Photo by G. Joyce.

In the North Pacific, sei whales Although sei whale feeding areas Commission (lWC) con­ winter in waters from lat. 20 0 N to lat. are fairly well defined in all oceans, sidered the whales in the North 23°N, and summer from lat. 35°N to the location of wintering areas re­ Pacific as two stock units, but since 40 0 N (with a few individuals found at mains to a large degree a mystery, the capture of sei whales was pro­ lat. 50 0 N) (Masaki, 1976). In the Ant­ since sei whales migrate in the open hibited, the IWC considers only one arctic, the summer distribution (in­ ocean and are difficult to observe stock unit for management purposes. ferred from catch statistics) is mainly from shore. Research indicates, however, that from lat. 40 0 S to 50 o S, and the winter there may be at least three stocks Stock Identity distribution is as yet unknown. In the found within this large area. Masaki North Atlantic, the northern (sum­ Since most hunting (and hence (1976; 1977) suggests boundaries west mer) limit is thought to be lat. nON, research, which is usually conducted of 175°W between 175°W and although little is known of southern in association with whaling activities) 155°W, and east of 155°W, based on (winter) distribution (Jonsglird, 1966). occurs on feeding rather than mark-recapture studies, catch There is evidence of differential breeding grounds, the groupings distribution, and differences in baleen migration by reproductive class, with observed are generally feeding rather plate morphology. pregnant females leading waves of than breeding aggregations. The rela­ North Atlantic migration both into and out of the tionship of breeding groups to feeding feeding grounds (Matthews, 1938; groups is poorly understood. The IWC recognizes the following Gambell, 1%8). Pregnant females stocks in the north Atlantic: Nova North Pacific also tend to be found in higher Scotia, -, and latitudes (Masaki, 1976). At one time the International northeast Atlantic. There is also an in-

26 Marine Fisheries Review dication, inferred from catches, mark however, and if are absent, causes them to shed their baleen recoveries, and migration patterns, of they feed on euphausiids, or , that plates; this greatly impairs their a separation between the congregate in dense shoals near the feeding ability. on sei stock and the one off northeast New­ surface-notably superba whales by killer whales, Orcinus orca, foundland and (Mitchell and E. vallentini in the Antarctic; E. appears to be rare. Natural mortality and Chapman, 1977). Schmidly pacifica, inermis, T. rates are difficult to estimate, but ap­ (1981) speculates that a Gulf of Mex­ longipes, and T. spinifera in the pear to be about 7.5 percent per year ico/ stock exists, but this is North Pacific; and Meganyctiphanes in adults, perhaps somewhat greater questionable due to possible confu­ norvegica and T. inermis in the North in immature (Allen, 1980). sion with Bryde's whales, Atlantic. In some parts of the Nor­ Balaenoptera edeni (Leatherwood thern Hemisphere, they also feed ex­ Exploitation and Population Size and Reeves, 1983). tensively on small schooling History of Exploitation such as , mordax; sauries, Cololabis saira; and jack The earliest exploitation of sei By convention, sei whales are con­ mackerel, symmetricus. whales likely occurred in waters off sidered to belong to six separate In autumn, sei whales migrate northern , starting around the stocks in the Antarctic, based on the several thousand miles toward middle of the 17th century. The six IWC statistical areas developed us­ equatorial waters. During the winter Japanese method of capturing the ing blue, fin, and , they eat very little or fast for several nonbuoyant, fast-swimming Megaptera novaeangliae, data months, living off their fat reserves (including sei, fin, and humpback (Brown, 1962; Mackintosh, 1966). (Mackintosh, 1965). whales) involved netting the Mark-recovery data indicate links be­ before killing it, and then towing it to Reproduction tween sei whales in various areas, e.g., shore for processing for human con­ the Brazilian coast and the western The reproductive strategy of sei sumption. Until the introduction of half of Area II; the Natal coast of whales is similar to that of most other modern whaling in in 1864, South Africa with the eastern half of balaenopterid whales. The mating the Japanese were the only whaling Area III and the western half of Area covers about 5 months during nation that could effectively capture IV; and the western and southeastern the winter. Most females ovulate only rorquals (Tjijnnessen and Johnsen, Australian coasts and Area IV (lWC, once, but if they do not conceive, they 1982). 1977). Other than this information, may ovulate two or three times during we know nothing of potential one season. The single calf is born North Pacific breeding areas in the Southern after a gestation period of about 1 Since modern whaling was intro­ Hemisphere, and therefore cannot year, when it is about 4.4 m (14.5 feet) duced in Japan at the beginning of the delineate breeding stocks. Conse­ long. The calves are weaned on the 20th century, the sei whale has ac­ quently, sei whales are managed summer feeding grounds when they counted for a large proportion of the separately by IWC area. are 6-9 months old, and have attained total whale catch in Japanese waters. a length of about 9.0 m (30 feet). Both Catches ranged from about 300 to 600 Life History and Ecology attain sexual maturity between 5 per year from 1911 through 1955, and Feeding and 15 years of age. Adult females rose to 1,340 in 1959, remaining at bear a calf every 2 or 3 years. high levels until a large drop in 1971. During the summer, sei whales in­ (Gambell, 1968; Masaki, 1976; Rice, Sei whales off Japan were protected habit much the same range as fin 1977; Lockyer and Martin, 1983). after 1975. Catches of sei whales by whales in the higher latitudes and the Natural Mortality Japanese and Soviet fleets in the cold currents on the eastern sides of North Pacific and jumped the oceans, where food production is Important natural mortality factors from 260 in 1962 to over 4,500 in 1968 high. In general they range even far­ are unknown. The sei whale is usually and 1969, after which catches declined ther offshore than fin whales, and relatively free of ectoparasites, but is rapidly. Whaling ceased after 1975 tend to be nomadic. Sei whales very often heavily infected with en­ when this stock of sei whales was pro­ specialize on copepods when available doparasitic helminths; presumably tected. (mainly Calanus tonsus, C. this is because its diet is more catholic Except for harvests off British Co­ simillimus, and Drepanopus pec­ than that of the fin or lumbia in the late 1950's through the tinatus in the Antarctic; C. cristatus, (Rice, 1977). Some of these en­ mid-1960's, sei whale catches off the C. plumchrus, and C. pacificus in the doparasitic worms are frequently coasts of were fairly North Pacific; C. finmarchicus in the pathogenic, affecting especially the insignificant compared to fin and North Atlantic) (Nemoto, 1959; liver and kidneys. A disease of humpback whale catches. Catches in Kawamura, 1973, 1974). They are unknown origin affects 7 percent of this region rose from 39 in 1958 to more euryphagous than fin whales, the sei whales off , and over 600 in 1964 and 1965, after

46(4),1984 27 .0000

30000

/ ...... ·/l_fin blue- . i

~ u / \ 20000 j\ / I :. a U . ',i A\\,,; 10000

...... \ ...... \...... ,._ -.~...... 0,. -0 9~3-0--"--, 9"'!5~0 -~:::"":-, 9~6::-0 9:;7::0-....,:".~'980 gL2 ----.:=, g-r.-Ot:.:..:;;<:-=:..:., '=::'---:-, Year

Figure 2. -Catch of sei, fin, and blue whales in the Antarctic, 1920-75 (from the Bureau of International Whaling Statistics).

which the catch dropped to 14 by under 2,000 by 1976, and stopping en­ Southern Hemisphere 1968. Catch of sei whales in this tirely after sei whales were protected Estimates of early and current sei region stopped entirely after 1971. in 1977. whale population sizes (Table 1) were reported at the IWC Special Meeting North Atlantic Current and Pre-exploitation on Southern Hemisphere Sei Whales Stock Sizes When modern whaling began in (lWC, 1980). Norway in the late 1800's, blue whales North Pacific and then fin whales were the preferred Management species, although a few sei whales Ohsumi and Fukuda (1975) Sei whales have been especially dif­ were taken late each season after the estimated that the pre-expioitation ficult to assess as evidenced by the larger rorquals had migrated out of population of sei whales in the North number of special meetings on South­ the area. As blue and stocks Pacific was about 45,000 whales, with ern Hemisphere sei whales held by the declined, however, sei whale catches a current (1967) range of from 22,000 IWC since the early 1970's. During gained in importance. In the early to 37,000. the 1960's and early 1970's, it was years, most sei whale catches occurred North Atlantic thought that Southern Hemisphere sei in waters off Norway and Iceland, whales were at or near their unex­ although substantial catches were Mitchell (1974) estimated the cur­ ploited levels during the late 1950's. taken off Nova Scotia from 1967 to rent (1966) population ofsei whales to Later evidence suggested that sei 1972. Currently, the Icelandic stock is be 1,856 off Nova Scotia and 828 in the only one harvested in the North the . According to the Atlantic. Cetacean and Turtle Assessment Pro­ gramI, there may be as many as 2,273 Southern Hemisphere sei whales in U.S. Atlantic coastal waters. Table 1.-Estimates of early and cur· Antarctic exploitation began in rent sei whale population sizes by Iwe 1904, but in the early years statistical area in the Antarctic. preferred humpback, blue, and fin Population est. lCetacean and Turtle Assessment Program. whales. As stocks of these other Area 1930 1979 whales declined, catches of sei whales 1982. A characterization of marine and turtles in the mid- and north Atlantic areas I 6.900 1.600 began to increase, rising rapidly in the of the U.S. outer . Unpubl. II late 1950's and early 1960's (Fig. 2). manuscr., 450 p. Graduate School Oceanogr., III 22.400 1.1()()'1.200 Univ. Rhode lsI., Kingston, RI 02881. (Prep. IV 14,700 5,700 Sei whale catches peaked at over for U.S. Dep. Int., Bur. Land Manage. under V 11,2()()'12,300 1,1()()'2,900 20,000 in 1964, declining rapidly to Contr. AA551-CT8-48.) VI 7,900-8,100 300-360

28 Marine Fisheries Review whales were increasing prior to the Hemisphere. Discovery Rep. 35:35-133. Pacific. Rep. Int. Whaling Comm., Spec. International Whaling Commission. 1977. Issue 1:71-79. 1950's, and that they were at their Report of the special meeting of the Scientific Matthews, L. H. 1938. The sei whale, Bal­ "initial" size early in this century. Committee on Sei and Bryde's whales. Rep. aenoptera borealis. Discovery Rep. However, this later evidence has also Int. Whaling Comm., Spec. Issue 1:1-9. 17:183-290. ____. 1980. Report of the special Mitchell, E. D. 1974. Canada progress been questioned so that the true situa­ meeting on Southern Hemisphere sei whales. report on whale research, May 1972 to May tion is unclear. The basic indices of Rep. Int. Whaling Comm. 30:493-511. 1973. Rep. Int. Whaling Comm. 24:196-213. abundance used to assess sei whales Jonsgll.rd, A. 1966. The distribution of Bal­ ____, and D. G. Chapman. 1977. aenopteridae in the North Atlantic Preliminary assessment of stocks of north­ have been sightings per unit of effort Ocean. In K. S. Norris (editor), Whales, west Atlantic sei whales (Balaenoptera and catch per unit of effort. Often, dolphins, and , p. 114-124. Univ. borealis). Rep. Int. Whaling Comm., Spec. Calif. Press, Berkeley. Issue 1:117-120. these two indices have resulted in Kawamura, A. 1973. Food and feeding of Nemoto, T. 1959. Food of baleen whales substantially different estimates for sei whales caught in the waters south of 40 0 N with reference to whale movements. Sci. the same stock area. In the Southern in the North Pacific. Sci. Rep. Whales Res. Rep. Whales Res. Inst., 14:149-290. Inst., Tokyo 25:219-236. Ohsumi, S., and Y. Fukuda. 1975. On the Hemisphere, sei whale catches peaked ____. 1974. Food and feeding ecology estimates of exploitable population size and during the mid-1960's as preference in the southern sei whale. Sci. Rep. Whales replacement yield for the Antarctic sei whale shifted from fin to sei whales and then Res. Inst., Tokyo 26:25-144. by use of catch and effort data. Rep. Int. Leatherwood, S., and R. R. Reeves. 1983. Whaling Comm. 25:102-105. dropped to low levels during the The Sierra Club handbook of whales and Rice, D. W. 1977. Synopsis of biological 1970's. In the North Pacific, there dolphins. Sierra Club Books, San Franc., data on the sei whale and Bryde's whale in the 302 p. eastern North Pacific. Rep. Int. Whaling have been no sei whale catches since Lockyer, C, and A. R. Martin. 1983. The Comm., Spec. Issue 1:92-97. 1976; Iceland, however, still takes sei whale off western Iceland: II Age, growth, Schmidly, D. J. 1981. Marine mammals of some sei whales in the North Atlantic. and reproduction. Rep. Int. Whaling the southeastern coast and Gulf Comm. 33:465-476. of Mexico. U.S. Wildl. Serv., BioI. Mackintosh, N. A. 1965. The stocks of Servo Program, FWS/OBS-80/41, 163 p. whales. Fish. News (Books) Ltd., London, Tomilin, A. E. 1957. Zveri SSSR i prilez­ Literature Cited 232 p. hashchikh stran (Mammals of the U.S.S.R. __...,....,._. 1966. The distribution of south­ and adjacent countries.). Volume 9. Allen, K. R. 1980. Conservation and man­ ern blue and fin whales. In K. S. Norris Kitoobraznye (). Izd. Akad. Nauk agement of whales. Univ. Wash. Press, (editor), Whales, dolphins, and porpoises, p. SSSR, Moscow, 756 p. [In Russ., Transl. by Seattle, 110 p. 125-144. Univ. Calif. Press, Berkeley. Isr. Program Sci. Transl., 1967, 717 p.I Brown, S. G. 1962. The movements of fin Masaki, Y. 1976. Biological studies on the Avail. from U.S. Dep. Commer. , Natl. Tech. and blue whales within the Antarctic zone. North Pacific sei whale. Bull. Far Seas Fish. Inf. Serv., Springfield, Va., as IT65-50086. Discovery Rep. 33: I-54. Res. Lab. (Shimizu) 14:1-104. TjIlnnessen, J. N., and A. O. Johnsen. 1982. Gambell, R. 1968. Seasonal cycles and __-,-----_. 1977. The separation of the The history of modern whaling. Univ. reproduction in sei whales of the Southern stock units of sei whales in the North Calif. Press, Berkeley, 798 p.

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