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Cetacean Assessment & Ecology Program

The Ice Whale in the Sea of Okhotsk

Bowhead whales, Balaena mysticetus, are found only in the Northern Hemisphere and are closely associated with sea ice—so much so that they are known to Alaskan and other native people as the “ice whale.” Currently, five populations of bowheads are recognized. The best known one is in the “western” Arctic off Alaska and western Canada; this group inhabits the Bering, Chukchi, and Beaufort Seas and is duly known as the “BCB” stock. There are also three recognized populations in the North Atlantic off eastern Canada, Greenland, and the Norwegian island of Spitsbergen.

The fifth bowhead whale population is an apparently separate and historically isolated group in the Okhotsk Sea (OS). Comparatively little is known about this stock. Certainly, the population was greatly reduced by whaling in the 19th century and, more recently, by illegal catches made by the U.S.S.R. The typically difficult conditions with which bowhead whale biologists must contend are exacerbated in the Okhotsk Sea due to the remoteness of the area, the low human population size, and the absence of development and facilities in much of the region, notably in the northern portion of this sea.

see caption
Figure 1. Distribution of bowhead whales in the Okhotsk Sea according to whale catches plotted by Townsend (1935).

Recently, for a project funded by the U.S. Marine Mammal Commission and submitted to the journal Mammal Review (Ivashchenko and Clapham in press), we reviewed current knowledge regarding bowhead whales in the Okhotsk Sea, concentrating especially on their seasonal distribution (both historically and today) and relative abundance. In addition to well-known historical materials and other publications, we drew upon previously untranslated Russian language reports of marine mammal surveys in the region. We reviewed the available literature on OS bowheads in both English and Russian. This literature can be broadly divided into three types or sources: 1) historical information, largely whaling data; 2) Japanese sighting surveys; and 3) Russian or Soviet reports and papers—in most cases previously unavailable in English—giving results of surveys (some directed and others opportunistic or focused on other taxa). The majority of recent information comes from the last source, which is not surprising given that most of the Okhotsk Sea lies within the jurisdiction of the Russian Federation (and formerly of the Soviet Union). The quality of individual Russian reports varies considerably from quite good to very vague or confusing; however, our access to both English and Russian texts has provided greater detail than has been possible in past attempts to clarify the results of these surveys.

The Okhotsk Sea is the world’s ninth largest body of water; it is bounded by mainland Russia to the west and north, the Kamchatka Peninsula to the east, and the island of Hokkaido (Japan) and the Kuril Islands to the south. Because of strong seasonal productivity, the region supports large numbers of marine mammals, including several species of large whales. In winter, the Okhotsk Sea is primarily covered by ice except for waters near Kamchatka and the Kuril Islands. Overall, the Okhotsk Sea possesses physical and oceanographic characteristics of both Arctic and temperate seas.

The Okhotsk Sea was the site of an intensive 19th-century whale fishery that was dominated by American whalers, although other nationalities (notably British and French) also operated there. The renowned whaler and naturalist Charles Melville Scammon (1874) noted, “The Okhotsk Sea at one time equaled if not surpassed the Arctic as a productive whaling ground.” Despite this history, the OS fishery remains poorly documented. Whaling for bowheads in the Okhotsk Sea began sometime around 1846 in Taouyskaya Bay (near Magadan in the northern Okhotsk Sea). By 1854, the Okhotsk Sea became the center of much whaling activity for a few years, and by 1860 about 200 whaling vessels were operating, primarily in the Shantar area. Scammon provides a detailed and colorful description of the whaling business at Shantar, including a note that in the early years of the fishery the bays were so full of whaling ships that extreme care had to be taken to avoid collision in the dense fog and ice that occurred there, notably at the beginning of the whaling season in June. Evidently the waters around Shantar were characterized by considerable bioluminescence; Scammon adds the note that, as summer advanced and daylight became shorter, “night-whaling” was frequently practiced, with the “phosphorescent light caused by the whale’s movements in the water [showing] quite distinctly his whereabout.”

The total number of catches remains unclear, and various efforts to estimate the original population size have yielded substantially different numbers. After the OS populations of bowheads and right whales had been rendered commercially extinct, whalers paid no attention to the area until 1967, when the Aleut whaling fleet from the U.S.S.R. began to hunt bowhead whales in the Shantar region. Because bowheads had long been protected by the International Whaling Commission, and because the U.S.S.R. was a signatory to the International Convention for the Regulation of Whaling (1946), all of these catches were illegal; the bowhead takes were a small part of a large worldwide campaign of illegal Soviet whaling (Clapham and Ivashchenko 2009). The total number of Soviet catches of bowheads in the Okhotsk Sea during the period of illegal whaling is unknown. However, this hunting again depleted the already small population and, thereby, further inhibited its recovery.

There is no good estimate of current abundance for bowhead whales in the Okhotsk Sea, although some scientists have assumed from general sighting rates since the 1980s that it is in the low hundreds. Genetic comparisons of OS and BCB bowheads using both mitochondrial DNA and microsatellites have revealed significant genetic differences between the two populations, consistent with a common ancestry but no mixing in the recent past.

In a fascinating and often amusing memoir from 1888, the whaler Otto Lindholm noted reports that some bowheads killed in the Okhotsk Sea had old harpoons embedded in them, bearing the names of whaling ships that had only whaled in the Arctic. However, he largely discounted this evidence for mixing between the two populations, noting that it was common practice for harpoons and other whaling equipment to be sold in the major Hawaiian provisioning and layover port of Honolulu (and, presumably, also in Lahaina). Scammon (1874) states, “no Bowheads of the Okhotsk Sea have ever been seen passing in or out of the passages of the Kurile Islands, or from the Okhotsk to Behring Sea, or Arctic whales passing to the Okhotsk.” On the basis of current evidence, there is no reason to doubt the current belief that OS bowheads constitute a discrete population and never leave the Okhotsk Sea.

Information on historical and current distribution comes from whaling records (Fig. 1) and from modern (notably Russian/Soviet) marine mammal surveys (Fig. 2). Little is known about winter distribution, but sightings of bowheads in pack ice in the Okhotsk Sea and elsewhere contradict the popular view that this species winters exclusively along the ice edge or in polynyas. In spring and summer, known bowhead concentrations occur in Shelikhov Bay and at Shantar. Although historical whaling data show bowheads in Shelikhov Bay in summer and early autumn (Fig. 1), recent sightings in this area have not occurred later than June. However, extensive 19th-century catches were made over much of the northern Okhotsk Sea, and the present range and habitat use of the population is likely broader than existing data suggest. There is equivocal evidence for age/class segregation between Shantar and Shelikhov Bay, with the former hosting immature whales and lactating females and the latter used by adults.

map, see caption
Figure 2. Reported sightings of bowhead whales in the Okhotsk Sea from 1967 to the present.

Overall, it is apparent from our review that the bowhead whale population in the Okhotsk Sea is separate from the closest neighboring stock in the BCB region, remains relatively small and unrecovered, and probably still occupies much of its historical range in the northern Okhotsk Sea, from Shantar to Kashevarova Bank and Shelikhov Bay.

There is little information regarding current threats to this population, although at least one whale has been reported killed through entanglement in a deep-water crab fishery; anecdotal reports of other entanglements exist. Given the population’s continued endangered status, further work on Okhotsk bowheads is urgently required. Further assessment of the status and conservation needs of this population cannot be undertaken without dedicated surveys of known and likely habitats in the northern Okhotsk Sea. Current knowledge would suggest that future effort should focus on the areas identified above (Shantar, the Taouyskaya Bay area south of Magadan, Kashevarova Bank, and Shelikhov Bay). However, prior to conducting such surveys, it would be useful to revisit historical whaling data and clarify the extent of overlap between bowheads and right whales in the Okhotsk Sea; this information, together with more recent data summarized here, could then be used to identify potentially key habitats and to better plan future surveys. Such surveys, as well as satellite tagging to assess individual movements, are critical for the future management of this once-heavily exploited population.

By Yulia Ivashchenko and Phil Clapham

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