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The IUCN Red List of Threatened Species

Eschrichtius robustus (Northwest Pacific (Asian) stock)

 – Critically Endangered

Taxonomy

Kingdom: ANIMALIA
Phylum: CHORDATA
Class: MAMMALIA
Order: CETACEA
Family: ESCHRICHTIIDAE
Scientific Name: Eschrichtius robustus (Northwest Pacific (Asian) stock)
Species Authority: (Lilljeborg, 1861)
Common Name/s:
English—GRAY WHALE, GREY WHALE

Assessment Information

Red List Category & Criteria: CR D    ver 2.3 (1994)
Year Assessed: 2000
Assessor/s: Weller, D. & Brownell R.L., Jr. (Cetacean Specialist Group)
Evaluator/s: Reeves, R. & Taylor, B.L. (Cetacean Red List Authority)
Justification: This subpopulation was hunted to near extinction, remains severely depleted, and has yet to demonstrate a population recovery trend similar to that evident for eastern north Pacific Gray Whales. In addition, the potential impacts of industrial activity throughout the known range of this population represents a poorly understood threat. The basis for a Critically Endangered listing is that the subpopulation is geographically distinct, and plausibly contains less than 50 reproductive individuals.
History:
1996-Endangered (Baillie and Groombridge 1996)

Geographic Range

Range Description: Migratory between the west central Sea of Okhotsk (summer-fall) and the South China Sea (winter). Individuals remain in shallow, mainly nearshore waters year-round, except when crossing the La Perouse and Tartarskiy Straits off the southern end of Sakhalin Island, Russia; similar open-water passages may also be encountered during north-south migrations in the Yellow and East China Seas.

Key areas of distribution include the summer feeding grounds off northeastern Sakhalin Island, Russia (52°50’N 143°20’E). Known portions of the north-south migratory route include regions off the eastern shore of Sakhalin Island in the Okhotsk Sea (Berzin in press), along the eastern shore of mainland Russia near the La Perouse and Tatarskiy Straits (Berzin in press), and off the eastern shore of the Korean peninsula (Andrews 1914, Brownell and Chun 1977). In addition, gray whales were once hunted by net fishermen off the eastern shore of Honshu, Japan (Omura 1984), and occasional gray whale sightings were reported off the Pacific coast of southern Japan between 1959-1997 (Kato and Tokuhiro 1997). Whaling records indicate that peak gray whale numbers off Korea occurred in two seasonal pulses, one presumably during the southward migration between December and January, and the other between March and April during the northward migration (Andrews 1914, Kato and Kasuya in press).

Winter calving and mating areas for this population remain unknown. Whalers working off Ulsan, Korea, found that a majority of reproductive females taken between December-January were carrying near-term fetuses and were thought to be within two to three weeks of parturition. Based on these observations, and his own measurement of one 4.76 m fetus, Andrews (1914) suggested that calves were probably born somewhere off the southern end of the Korean Peninsula, and that this region represented the probable southern terminus of the winter migration. Several lines of evidence, however, suggest that Andrews (1914) miscalculated. Rice and Wolman (1971) reported an average near-term fetus size of 4.62 m for eastern gray whales taken off central California between December and January. Thus, the observed fetus size, seasonal timing, and latitudinal position (around 34° N) reported for Korea and central California closely correspond. However, eastern North Pacific gray whales migrate to breeding areas as far south as 20°-27°N off Baja California (Wolman 1985). While some western gray whales may terminate their southern migration approximately 7°-14° farther north than eastern gray whales, historical records indicate that they occurred as far south as the Yellow Sea, East China Sea, and South China Sea (Henderson 1972, 1984, 1990; Wang 1978, 1984; Omura 1988, Kato and Kasuya in press). Wang (1984) presented evidence that gray whales may have ranged at least as far south as 20°N off Hainan Island in southeastern China. In addition, Omura (1974) suggested that an alternative or additional calving and mating area was in the Seto Inland Sea (34°-35°N) off southern Japan, but little direct evidence is available to support this idea.
Countries: Native:

China; Japan; Korea, Democratic People's Republic of; Korea, Republic of; Russian Federation
FAO Marine Fishing Areas: Native:

Pacific-northwest

Population

Population: This subpopulation was thought to be extinct as recently as 1972 (Bowen 1974), but is known to survive today as a small remnant subpopulation (Berzin 1974, Brownell and Chun 1977, Weller et al. 1999). Aerial and ship-based sighting records in the Okhotsk Sea between 1979 and 1989 indicated that gray whales aggregated predominantly along the shallow-water shelf of northeastern Sakhalin Island, Russia, and were most common off the southern portion of Piltun Lagoon (Blokhin et al. 1985; Berzin 1988, 1990, 1991, in press; Blokhin 1996). The current population size of western gray whales is unknown, but suspected to be approximately 100 (Weller et al. 1999). Two non-quantitative population estimates of 100 (Blokhin 1996) and 250 (Vladimirov 1994) have been reported in the Russian literature, but neither of these are valid. The estimate of 250 by Vladimirov (1994) was derived from Russian cetacean sighting records collected between 1979-1992. These records were collected from a variety of observation platforms, during different seasons, and employed mostly non-systematic sampling strategies. Although counts may be inflated by repeated observations of the same individuals, the highest count reported by Vladimirov (1994) during any sampling period was 34 gray whales observed off northeastern Sakhalin Island in 1989. The foundation for how this count of 34 was extrapolated to a population estimate of 250 is not described or based on any apparent quantitative calculation. The estimate of 100 by Blokhin (1996) was based on eight shore counts and one helicopter survey conducted between July-August of 1995 along the northeastern Sakhalin Island coast. The highest number of whales counted on any one day during this period was 42. As was true for the estimate of 250 by Vladimirov (1994), the logic for how Blokhin (1996) took the highest count of 42 and extrapolated to a population estimate of 100 is not described. Both of these estimates should be considered unreliable and not used as the basis for understanding the current population status of western gray whales.

Recent photo-identification studies (1994-1995 and 1997-1999) on the primary feeding grounds off northeastern Sakhalin Island have identified a total of 88 individual whales (Weller et al. 2000). These photo-identification data indicate high levels of annual return and pronounced seasonal site fidelity. While new individuals continue to be identified annually, the rate at which this is occurring is near asymptote. Only 20 previously unidentified whales (excluding calves) were photographed during 91 days of effort between 1998-1999. This finding suggests that a majority of the population had been identified between 1994-1997 (Weller et al. 2000). Between 1995-1999, 11 reproductive females and their 13 calves were observed (Brownell et al. 1997, Weller et al. 1999, 2000). Two calves were observed in 1995, 1997, and 1999, and seven calves were sighted in 1998. Crude birth rates ranged between a low of 2.8% in 1999 to a high of 13.0% in 1998. Of the 11 calves identified between 1995-1998, seven (63.3%) have not been re-sighted on the Sakhalin feeding grounds subsequent to their birth year.

Estimating the number of whales inferred to be capable of reproduction, called the number mature for short, is problematic for this population because there are no direct data and demographic estimates depend on the population growth rate, which is unknown. We take two approaches to estimating plausible, conservative numbers mature. Rice and Wolman (1971) found that 24.0% of the eastern gray whales in their study were sexually immature, and suggested that the total proportion of immature animals was more likely to be 44.0–61.0%. Using the minimum estimate of 88 western gray whales (Weller et al. 1999, 2000) and using the proportion immature from Rice and Wolman (1971), the number of mature whales in the western subpopulation ranges between 34 and 49.

However, the eastern gray whale subpopulation was growing at the time Rice and Wolman conducted their study, and would therefore be expected to be composed primarily of immature animals. The proportion mature would be very different for a stable population. The proportion mature for a stable population can be estimated using age-specific birth and death rates. Rice and Wolman (1971) reported the mean age of sexual maturity for eastern gray whales to be eight years (range = 5-11). Reilly (1992) estimated adult survival to be 0.95. Although there are no data for first year survival in gray whales, survival should not differ strongly from that for humpback whales, which is 0.875 (Barlow and Clapham 1997). For a stable population the proportion mature is 63%, which for the estimate of 88 whales results in 55 mature animals. However, this estimate assumes that all mature adults are capable of reproduction. If this small population is not growing then it is plausible that reproduction has been compromised because the population is so small. Detailed data from another small population that has failed to recover could provide a pessimistic scenario. Only 70% North Atlantic right whales (Eubalaena glacialis) females known to be mature have actually reproduced. If we assume that all males reproduce but only 70% of the females reproduce, then 85% of the sexually mature animals are capable of reproduction. Thus, of the 55 mature western gray whales, 47 would meet the IUCN definition of mature.
Population Trend: Unknown

Habitat and Ecology

Habitat and Ecology: Gray Whales are endemic to the North Pacific Ocean, having become extinct in the North Atlantic more than 150 years ago. The species is known for its long-distance migrations between subtropical calving and mating grounds near continental coasts and high-latitude feeding grounds in the Arctic and Subarctic (Rice and Wolman 1981, Swartz 1986). As bottom-feeding specialists, Gray Whales aggregate during summer and fall in shallow shelf waters and offshore banks where benthic and epibenthic crustacean communities are concentrated (Nerini 1984, Oliver et al. 1984, Kim and Oliver 1989). Traditional nearshore migratory routes connect high-latitude feeding areas with warm-water coastal and inshore wintering grounds. Today, the primary summer-fall feeding habitat for western gray whales is located off the northeastern coast of Sakhalin Island, Russia. The calving and mating grounds for this population are presently unknown, but strongly suspected to be in coastal waters of the South China Sea.
System: Marine
List of Habitats:
9.1Marine Neritic - Pelagic
10.1Marine Oceanic - Epipelagic (0-200m)

Threats

Threats: The decline in the Northwest Pacific Gray Whale subpopulation can be largely attributed to modern commercial whaling off Russia, Korea, and Japan between the 1890s and 1960s. This subpopulation has been legally protected under the International Convention for the Regulation of Whaling since 1946. The Republic of Korea and China, however, did not join the International Whaling Commission (IWC) until 1978 and 1980, respectively. Prior to their IWC membership, at least 67 Gray Whales were killed between 1948-1966 off the Republic of Korea, and the lack of catch reports from 1967 to 1980 does not necessarily indicate the absence of Gray Whale takes by either of these countries during that fourteen year period (Brownell and Chun 1977). The Democratic People’s Republic of Korea, recognized for its long-term involvement in coastal and pelagic whaling operations, is presently not a member of the IWC and nothing is known about whaling in this country for the past fifty years.

Current threats to the western gray whale population include continued mortality from an undetermined level of hunting (Brownell 1999, Brownell and Kasuya 1999), and incidental catches in the extensive coastal net fisheries off southern China (Zhou and Wang 1994). The substantial nearshore industrialization and shipping congestion throughout the migratory corridors of this population also represent potential threats by increasing the likelihood of exposure to chemical pollution and ship strikes. Present and planned large-scale offshore gas and oil development in the South China Sea, and within 20 km of the only known feeding ground for western gray whales off northeast Sakhalin Island in the Okhotsk Sea, is of particular concern (Brownell et al. 1997, Würsig et al. 1999 and 2000, Weller et al. 2000). Activities related to oil and gas exploration, including high-intensity geophysical seismic surveying, drilling operations, increased ship and air traffic, and oil spills, all pose potential threats to gray whales. Disturbance from underwater industrial noise may displace whales from critical feeding, migratory, and breeding habitat (Bryant et al. 1984, Richardson et al. 1995). Physical habitat damage from drilling and dredging operations, combined with possible impacts of oil and chemical spills on benthic prey communities also warrants concern.
List of Threats:
3.1.3Harvesting (hunting/gathering) - Food - Regional/international trade (past)
4.1.1.3Accidental mortality - Bycatch - Fisheries-related - Entanglement (ongoing)
4.2.2Accidental mortality - Collision - Vehicle collision (ongoing)
6.3.3Pollution (affecting habitat and/or species) - Water pollution - Commercial/Industrial (future)
6.3.6Pollution (affecting habitat and/or species) - Water pollution - Oil slicks (future)
8.3Changes in native species dynamics - Prey/food base (future)
9.2Intrinsic factors - Poor recruitment/reproduction/regeneration (ongoing)
10.4Human disturbance - Transport (present, future)

Conservation Actions

Conservation Actions: Gray Whales are protected from whaling in Russia, Japan, the Republic of Korea, and China, as each of these countries belongs to the IWC. Regardless of this protection, at least one illegal take of a western Gray Whale occurred in 1996 off Hokkaido, Japan (Brownell 1999, Brownell and Kasuya 1999). No other conservation measures exist. In response to the concerns regarding the viability of this population, a joint research project under the U.S.-Russian Environmental Agreement (Marine Mammal Project) was initiated in 1995. Objectives of this investigation were to examine the conservation status, occurrence, distribution, behavior, and potential human-related disturbance of Gray Whales on their summer feeding grounds off the northeastern coast of Sakhalin Island. This ongoing project includes: aerial surveys, shore-based behavioral observations and theodolite tracking, acoustic monitoring, biopsy sampling, and photo-identification (Brownell et al. 1997, Würsig et al. 1999 and 2000, Weller et al. 1999 and 2000).

Bibliography

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Citation: Weller, D. & Brownell R.L., Jr. 2000. Eschrichtius robustus (Northwest Pacific (Asian) stock). In: IUCN 2007. 2007 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 08 September 2008.
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