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Gray whale (northeast Pacific DPS)

The gray whale (Eschrichtius robustus) occurred in the North Atlantic Ocean until the 17th or early 18th century [1]. Currently, however, this species is found only in the North Pacific [2]. Intense whaling led to the extirpation of Atlantic gray whales and decimated populations in the Pacific [1]. It is estimated that only between 4,000 and 5,000 gray whales remained by the mid 1800s [3]. Protection from commercial whaling, enacted in 1947, allowed the remaining gray whale populations in the North Pacific to increase [3]. The eastern North Pacific stock along the west coast of North America reached near pre-exploitation numbers in the 1990s and was officially removed from the list of endangered species on June 16, 1994 [1]. The western North Pacific or "Korean" stock, which lives along the coast of eastern Asia, has not increased in number and remains endangered [3].

The Eastern North Pacific stock of gray whales moves along the west coast from summer feeding grounds in the Bering and Chukchi Seas, to nearly landlocked lagoons and bays along the west coast of Baja California where calves are born from early January to mid-February [4]. Since 1967, shore-based counts of migrating gray whales have been conducted at strategic points in California where migration routes pass close to land [4]. In 1967/68 the abundance of this stock was estimated to be 13,095 (95% C.I. 10,593-15,597) [4]. By 1997/98 numbers had increased to 26,635 (CV = 0.1006) [2]. The estimated the annual rate of increase for these years was 2.52% (95% CI: 2.04%-3.12%) [2]. In 1999 and 2000, however, a large number of gray whale strandings (273 and 355) occurred along the west coast of North America (this is compared to an average of 38 stranding per year over the previous 4 years) [2]. The reason for these strandings is not known, but causes could include starvation, chemical contaminants or natural toxins, disease, or direct anthropogenic factors such as ship strikes [2]. It could also be the result of changes in wind shifts or currents causing more carcasses to be washed ashore [2]. Population estimates in 2001 and 2002 dropped to 18,761 and 17,414 respectively [5]. This drop in numbers compared to previous years could indicate an actual population decline due to increased mortality or could be due to an unusual number of whales not migrating as far south as the counting station [5]. Some researchers suggest that it could indicate this population is reaching its carrying capacity [5].

Although the gray whale is no longer considered endangered, there are still threats to gray whale populations [1]. Between 1996 and 2000, subsistence hunters in Alaska and Russia took an average of 97 gray whales per year [1]. Because gray whales spend a great deal of time near coastlines, they are also susceptible to ship strikes, coastal development, pollution, military activities, exploration and development of oil and gas resources, and increasing harassment by the whale-watching industry [1].

[1] NOAA Fisheries, Office of Protected Resources. Cetaceans: Whales, Dolphins, and Porpoises: Gray Whale. Website http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/gray_whale.doc (Accessed on 12/6/05).
[2] NOAA Fisheries. 2003. Stock Assessment Report. Gray Whale (Eschrichtius robustus): Eastern North Pacific Stock. Revised 3/20/02. National Oceanic and Atmospheric Administration, Washington, D.C.
[3] Noecker R.J. 1998. Congressional Research Service, Report for Congress: Endangered Species List Revisions: A Summary of Delisting and Downlisting. Made available by National Council for Science and the Environment. Washington D.C. http://www.ncseonline.org/NLE/CRSreports/Biodiversity/biodv-18.cfm
[4] Reilly, S.B., D.W. Rice, and A.A. Wolman. 1983. Population Assessment of the Gray Whale, Eschrichtius robustus, from California Shore Censuses, 1967-80. Fisheries Bulletin 18(2): 267-279.
[5] Rugh, Dave. 2004. Gray Whale Census (2001-2002). National Marine Mammal Laboratory, Alaska Fisheries Science Center. http://nmml.afsc.noaa.gov/CetaceanAssessment/GrayWhale/GrayCensus01-02.htm

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