04 Blue Mar Fish 61(1)

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 27/09/2021 05:17:25 Link to Item http://hdl.handle.net/1834/26411 The Blue Whale, Pygmy Blue Whale, and the Antarctic or True Blue Whale Introduction in the mid latitude waters of the south- within this ocean basin (Ohsumi and ern Indian Ocean and north of the Ant- Wada, 1974; Mizroch et al., 1984a; The Northern Hemisphere blue arctic Convergence is the smallest Barlow et al., 1994b; Braham3; Gilpatrick whale, Balaenoptera musculus muscu- (Ichihara, 1966; Omura et al., 1970; Kato et al.66). One such tentative stock desig- lus Linnaeus 1758; the pygmy blue et al., 1995; Gilpatrick et al.66). Distin- nation is for blue whales occuring dur- whale, Balaenoptera musculus brevi- guishing between the subspecies is dif- ing winter off Baja California and in the cauda Ichihara 1966; and the true blue ficult at sea and, therefore, information Gulf of California (Fig. 4). Photo-iden- whale65 , Balaenoptera musculus inter- on population size and distribution for tification studies have shown that indi- media Burmeister 1871, are members each subspecies may be unreliable. viduals from these concentrations travel of the Balaenopteridae family whose in summer and fall to waters off Cali- Distribution and Migration subspecies contain the largest animals fornia (Calambokidis et al.,1990; ever known to have lived on Earth Blue whale distribution is worldwide Barlow et al.,1997; Sears et al.67). Pre- (Rice12). Adult blue whales can attain (Fig. 24). Presumably they follow a liminary studies of these California/ lengths of about 30 m and weigh up to migration pattern of seasonal north- Mexico whales, based on body-length 160 t in the Southern Oceans (Mackin- south movements between summering data from whaling records and aerial tosh, 1942). In the North Atlantic and and wintering areas, but some evidence photogrammetry, indicate that they are North Pacific, their maximum lengths suggests that individuals in certain ar- morphologically distinct from blue have been recorded at 27 m (True, 1904) eas remain in low latitudes year-round whales of the western and central North and 26.8 m (Reeves et al., 1985), respec- (Donovan, 1984; Yochem and Leather- Pacific (Gilpatrick et al.66). tively. They are gray in color (appear- wood, 1985; Reilly and Thayer, 1990). Acoustic monitoring has resulted in ing blue below the water surface) with The location of wintering areas is still blue whale vocalizations being recorded distinct gray and white mottling, while somewhat speculative (Jonsgård, 1966; off Oahu, Hawaii, and the Midway Is- their ventral surface is lighter in color. Mackintosh, 1966), whereas known lands (Northrop et al., 1971; Thompson Their dorsal fin is relatively small (Fig. summer feeding areas are in the rela- and Friedl, 1982), although sightings or 23). Like other balaenopterids, they tively high latitudes. Migratory routes are strandings in Hawaiian waters have not have fringed baleen plates instead of teeth not well known, mainly because blue been reported. Nishiwaki (1966) noted and ventral grooves which allow for the whales occur primarily in the open ocean. the occurrence of blue whales near the filtering of large quantities of water dur- Aleutian Islands and in the Gulf of North Pacific ing feeding on swarms of euphausiids. Alaska. However, as of 1987, there have Rice12 recognizes the B. musculus Blue whales are found along the been no blue whale sightings in these subspecies based on body size and geo- coastal shelves of North America and waters (Leatherwood et al., 1982; Stewart graphic distribution. B. m. intermedia, South America in the Pacific Ocean et al., 1987; Forney and Brownell68). No which occurs in the high latitudes of the (Rice, 1974; Clarke, 1980; Donovan, distributional information exists for the Southern Oceans, is the largest (maxi- 1984). The IWC Scientific Committee western North Pacific Ocean. mum length = 30 m), B. m. musculus of recognized one blue whale stock in the 67 Sears, R., M. Berube, and D. Gendron. 1987. the Northern Hemisphere is slightly North Pacific (Donovan, 1991). How- A preliminary look at the distribution and mi- smaller (maximum length = 27 m), and ever, there is increasing evidence sug- gration of blue whales (Balaenoptera musculus) B. m. brevicauda (pygmy blue whale) gesting that more than one stock exists in the northeast Pacific, based on the photo-iden- tification of individuals (Abstr.). In Proceedings of the Seventh Biennial Conference on the Biol- 65 B. m. intermedia is referred to in the literature 66 Gilpatrick, J. W., W. L. Perryman, and R. L. ogy of Marine Mammals, 1987, Miami, Fla. by three common names: Antarctic blue whale, Brownell. 1997. Geographic variation in North 68 Forney, K. A., and R. L. Brownell. 1996. Pre- southern ordinary blue whale, and the true blue Pacific and Southern Hemisphere blue whales liminary report of the 1994 Aleutian Island ma- whale. To avoid confusion, this review refers to (Balaenoptera musculus). Unpubl. doc. SC/49/ rine mammal survey. Unpubl. doc. SC/48/011, this subspecies as the “true” blue whale. 09, 33 p., submitted to Rep. Int. Whal. Comm. 15 p., submitted to Rep. Int. Whal. Comm. 38 Marine Fisheries Review Figure 23.—A blue whale surfacing. Note the mottled coloration and very small dorsal fin. J. M. Waite, NMML Collection. Figure 24.—Worldwide distribution of all blue whale species. Adapted from Mizroch et al. (1984a). The Costa Rica Dome (centered presence: 1) the standing stock of prey utilize the area. Blue whales have been roughly around lat. 9°N, long. 89°W) (i.e. euphausiids) that results from this sighted in the Dome area in all seasons, is a stationary eddy in the eastern tropi- highly productive area, 2) the aggrega- but there is a peak in occurrence from cal Pacific Ocean which appears to be tion of juvenile, nonmigratory whales, June through November. an important year-round habitat for blue 3) the occurrence of a resident stock of North Atlantic whales (Fig. 13) (Reilly and Thayer, Northern Hemisphere blue whales, or 1990). Reilly and Thayer (1990) sug- 4) temporal overlap, when both North- Blue whales are found from the Arc- gested four reasons for this year-round ern and Southern Hemisphere whales tic to at least the mid latitude waters of 61(1), 1999 39 the North Atlantic with occasional oc- Sightings have been reported from the for these areas. Off the coast of Oregon currences in U.S. Exclusive Economic Gulf of Aden, Persian Gulf, Arabian and Washington, no blue whales were Zone (EEZ)69 waters (Yochem and Sea, and across the Bay of Bengal to sighted during an aerial survey in 1991 Leatherwood, 1985; Wenzel et al., 1988; Burma and the Strait of Malacca (Fig. (Green et al.75) or during ship-based line CeTAP70; Gagnon and Clark71). These 12, 14) (Mizroch et al., 1984a). The transect surveys in 1996 (Barlow74). In whales are currently recognized as one migratory movements of these whales the eastern tropical Pacific, Wade and stock by the IWC (Donovan, 1991). are unknown. Gerrodette (1993) estimated 1,415 (CV Sightings of blue whales occur most = 0.243) blue whales from ship-based Southern Hemisphere frequently off eastern Canada. During line transect survey data. There are no winter, they are found in the waters off Blue whales in the Southern Hemi- statistically reliable population esti- Newfoundland. In summer, they are sphere are assigned to six stock areas mates for the eastern North Pacific north found in Davis Strait (Mansfield, 1985), designated by the IWC (Fig. 9) (Donovan, of the State of Washington or in the in the Gulf of St. Lawrence (from the 1991). These areas are consistent with the western North Pacific. Nonetheless, it north shore of the St. Lawrence River presumed blue whale feeding locations, appears that at a minimum there are estuary to the Strait of Belle Isle), and although reliable distributional informa- currently over 3,300 blue whales in the off eastern Nova Scotia (Fig. 6) (Sears tion on blue whales is still scarce. His- North Pacific (Wade and Gerrodette, et al.67). torical catch records indicate that the 1993; Barlow74). In 1992, the U.S. Navy and its con- true blue whale and the pygmy blue According to calculations based on tractors conducted an extensive acous- whale may be geographically segre- historic whaling data, there were an es- tic survey of the North Atlantic using gated (Kato et al., 1995; Brownell and timated 4,900 (no CV available) blue the Integrated Underwater Surveillance Donahue73). The distribution of the whales inhabiting the North Pacific prior System’s (IUSS) fixed acoustic array pygmy blue whale is north of the Ant- to commercial exploitation (Gambell, (Clark, 1995). This study provided in- arctic Convergence, while that of the 1976). Admittedly, estimates such as formation on the seasonality and geo- true blue whale is south of the Conver- these are rather speculative. graphic distribution of several baleen gence in the austral summer (Fig. 10) whale species’ vocalizations (Clark et (Kato et al., 1995). True blue whales North Atlantic al.72). Localizations of the sounds indi- occur mainly in the relatively high lati- Braham3 provided a population esti- cated concentrations of blue whales on tudes. During summer, the true blue mate for the entire North Atlantic of the Grand Banks off Newfoundland and whale is found close to the ice edge between 100 and 555 blue whales based west of the British Isles. One blue whale (south of lat. 58°S) with concentrations on history of catches and trends in was tracked acoustically for 43 days, dur- between lat.

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