The Great Whales: History and Status of Six Species Listed as Endangered Under the U.S. Endangered Species Act of 1973

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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

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- , 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 . Mead (1977) noted that Horwood (1987) reported that 75Ð85% 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 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 (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). This low-precision estimate scale exploitation of some previously taken off Nova Scotia (Mitchell, 1975b). is not considered a true index of abun- unobtainable large whale species. The Southern Hemisphere dance (Blaylock et al., 1995). The most North Pacific and Antarctic whaling recent estimates for the Iceland/Den- operations soon added this modern A total of 152,233 sei whales were mark Strait stock are 1,290 (CV = equipment to their arsenal. After blue caught in the Southern Hemisphere 0.603) whales from ship-based surveys and fin whales were depleted in most from 1910 through 1979 (Horwood, in 1987 and 1,590 (no CV) whales from areas, sei whales became the focus of 1987). Whaling in the Southern Oceans ship-based surveys in 1989 (Cattanach operations. In the 1950’s through originally targeted humpback whales. et al., 1993). Based on data from Dis- 1970’s, these whales were severely de- By 1913, this target species had become covery tag38 studies, Mitchell and pleted by commercial whaling opera- rare and the catch of fin and blue whales Chapman (1977) provided a population tions (Fig. 33). began to increase. As these species like- estimate for the Nova Scotia stock of wise became scarce, sei whale catches North Pacific between 1,393 and 2,248 whales, with a increased rapidly in the late 1950’s and minimum estimate of 870 for this stock. From 1910 to 1975, approximately early 1960’s (Mizroch et al., 1984c). Estimates in U.S. waters (Nova Scotia 74,215 sei whales were caught through- The catch peaked in 1964 at over 20,000 stock), derived from the Cetacean and out the North Pacific Ocean (Horwood, sei whales, but by 1976 this number Turtle Assessment Program (CeTAP) 1987). From the beginning of the 20th dropped to below 2,000 and the species data70 in 1982, are not considered statis- century, Japanese whaling operations received IWC protection in 1977. tically reliable because of low survey ef- consisted of a large proportion of sei Recently revealed Soviet whaling fort and inaccuracy in accounting for sub- whales. In local waters off Japan, 300Ð catch data from the years 1947 through merged (Blaylock et al., 1995). 600 sei whales were caught per year 1980 showed that over 17,000 more sei

61(1), 1999 55 whales were caught (total = 50,034) the Antarctic waters of the Southern 1980, 1994; IWC, 1992a). However, than were previously reported (33,001) Hemisphere. They range farther off- Murphy et al. (1988) and Fraser et al. to the IWC (Zemsky et al., 1995). One shore than fin whales in search of prey (1992) suggested that competition reason for this discrepancy may have concentrations. among whales and other krill predators been the misidentification of sei whales Sei whales are less prey-selective in the Antarctic is relatively low as fin whales in the original reporting. than fin whales. Sei whales consume (Clapham and Brownell, 1996). primarily copepods, but they also prey Current Exploitation on euphausiids and small schooling Reproduction From 1988 to 1995, there have been fishes when these species are locally Sei whales reach sexual maturity be- 12 reported takes of sei whales from the abundant (Table 15) (Mizroch et al., tween 5 and 15 years of age. Similar to North Atlantic (Table 10). All of these 1984c). This species seems to have the the fin whale, conception occurs dur- takes were off Iceland and West Green- greatest flexibility relative to other ing a 5-month period in the winter of land. However, the IWC set a catch limit balaenopterids in their feeding strategies, either hemisphere. After a gestation of zero for all stocks of sei whales be- using both “engulfing” and “skimming” period of around 12 months, a calf mea- ginning in 1985 (IWC, 1995b). to capture prey (Nemoto, 1959). suring about 4.4 m is born. Between 6 In the Southern Hemisphere, there is and 9 months after birth, the immature Life History and Ecology some evidence that sei whales may whale is weaned at a length of 9 m. The minimize direct interspecific competi- calving interval for sei whales ranges Feeding tion with the blue, fin, and minke whales from 2 to 3 years (Rice, 1977a; Lockyer Sei whales spend the summer feed- by foraging in warmer waters than do and Martin, 1983; Mizroch et al., 1984c). ing in the relatively high latitudes of the latter species, by consuming a rela- Natural Mortality both hemispheres, particularly along the tively wider variety of prey, and by ar- cold eastern currents of the North Pa- riving later on the feeding grounds than Information on natural mortality in cific and North Atlantic Oceans and in other baleen whales (Kawamura, 1978, sei whales is scant. The estimated an-

Figure 33.—A raft of harvested sei whales. NMML Collection.

56 Marine Fisheries Review nual natural mortality rate is around Human-related Mortality the injured or killed animals do not 7.5% (Allen, 1980). This mortality rate strand. One death was documented in Fisheries Interactions is relatively higher for fin and blue 1994, when a container ship arrived in whales and may be even greater among There have been no reports of sei Boston harbor with a sei whale carcass immature sei whales. Endoparasitic hel- whale mortality caused by fishing ac- on its bow. The crew estimated that the minths are commonly found in sei tivities in any eastern North Pacific fish- whale had been struck approximately 4 whales, and these infestations can result ery. However, Barlow et al. (1997) noted days before the ship pulled into port in pathogenic effects, especially when that a conflict may exist in the offshore (Waring et al., 1998). found in the liver and kidneys (Rice, drift gillnet fishery. Potential injury or Noise Disturbance 1977a). Mizroch et al. (1984c) mentioned mortality in this fishery may go unde- an unknown disease affecting approxi- tected because entangled sei whales Although little is known of sei whale mately 7% of the California sei whale may swim away carrying gear. acoustic behavior, hearing thresholds, population, which results in loss of ba- In U.S. waters of the North Atlantic, and tolerance of noise, they appear to leen plates and could hinder feeding. fisheries-related mortality or serious respond to approaching vessel traffic in Sei whale predation by killer whales injury was not reported in commercial relatively the same manner as blue and has not been reported. However, it is fishing activities from 1989 to 1995 fin whales. Responses to boats appear likely, given observations of killer (Blaylock et al., 1995; Barlow et al., to depend on the behavior of the ani- whale attacks on fin, blue, and sperm 1997). Total mortality and serious in- mals at the time of approach and the whales, that killer whale attacks result jury from fisheries-related incidents is speed and direction of the approaching in mortality or serious injury to imma- considered biologically insignificant, vessel. In general, however, sei whales ture or weakened individuals. If such but a comprehensive review of all fish- exhibit more avoidance behavior than attacks occur, they likely go undetec- eries has not been done. do fin whales when being approached ted by humans. Although they have not by a vessel (Gunther, 1949). Vessel Collisions been reported, shark attacks may also Classification Status result in mortality or serious injury to It is possible that ship strikes affect vulnerable sei whales (e.g. the very all stocks of sei whales but, due to their The sei whale was listed as endan- young or old and the ill or injured). pelagic nature, go unreported because gered under the ESA in 1973 and is pro- tected under the MMPA. Endangered status is applied to all sei whale stocks Table 15.—Sei whale prey items (Mizroch et al., 1984c). in U.S. waters (Anonymous, 1994b). Region Prey type Species Internationally, an IWC “Protected

Northern Hemisphere Fish Engraulis spp. (anchovies) Stock” classification has been assigned Cololabis spp. (sauries) to the North Pacific, Nova Scotia, and Trachurus spp. (jack mackerel) Southern Hemisphere stocks by the North Pacific Copepod cristatus Commission. Under this designation, C. plumchrus C. pacificus the IWC recognizes that these stocks are Euphausid Euphausia pacifica 10% or more below their maximum sus- Thysanoessa inermis tainable yield (MSY) levels, and there- T. longipes T. spinifera fore commercial whaling is prohibited North Atlantic Copepod Calanus finmarchicus (IWC, 1995b). Two of the North Atlan- Euphausid Meganyctiphanes norvegica tic stocks, Iceland/Denmark Strait and Thysanoessa inermis Eastern North Atlantic, have no formal Antarctic Copepod Calanus tonsus IWC classification; however, their catch C. simillimus Drepanopus pectinatus limits will remain at zero until the Com- Euphausid Euphausia superba (Antarctic krill) mission receives a comprehensive as- E. vallentini sessment of these stocks and until the

Table 16.—Factors possibly influencing the recovery of North Atlantic sei whale stocks under the ESA (1973) ¤4(a)(1), 1992 Amend. (Southern Hemisphere data is not available).

Factor North Atlantic North Pacific

1. Present or threatened destruction or modification Unknown Unknown of habitat

2. Overutilization for commercial, subsistence, recre- Icelandic harvest; whale watching, scientific research, photog- Whale watching, scientific research, photography, and ational, scientific, or educational purposes raphy, and associated vessel traffic associated vessel traffic

3. Disease or predation Parasitic helminth infestations Unknown

4. Other natural or man-made factors Vessel collisions Vessel collisions

61(1), 1999 57 current moratorium on commercial of sei whale status awaits the collection (Anonynous7). This plan attempts to whaling is ended. of more reliable information on stock outline steps towards recovery of the sei Since Braham’s 1991 status review3, structure, distribution and migration whale through focused research priori- there has been little advance in the ac- patterns, trends in abundance, causes of ties designed to increase our under- curacy and availability of population mortality, and factors influencing the standing of sei whale biology, identify estimates or stock identity. The factors recovery of sei whale stocks, as well as current threats to their survival, allevi- possibly influencing the status and re- the development of objective delisting ate the possibility of future threats, and covery of sei whales are summarized in criteria. A joint Recovery Plan has been encourage international cooperation. Table 16. At this time, any reevaluation developed for both sei and fin whales

58 Marine Fisheries Review