Two Pacific Ocean populations are known to exist: one of not more than 130 individuals (according to the most recent population assessment in 2008) whose migratory route is presumed to be between the Sea of Okhotsk and southern Korea, and a larger one with a population between 20,000 and 22,000 individuals in the eastern Pacific traveling between the waters off Alaska and Baja California Sur.
The western population is listed as critically endangered by the IUCN. No new reproductive females were recorded in 2010, resulting in a minimum of 26 reproductive females being observed since 1995. Even a very small number of additional annual female deaths will cause the subpopulation to decline. In 2007, S. Elizabeth Alter used a genetic approach to estimate prewhaling abundance based on samples from 42 California gray whales, and reported DNA variability at 10 genetic loci consistent with a population size of 76,000-118,000 individuals, three to five times larger than the average census size as measured through 2007.
NOAA conducted a new populations study in 2010-2011; those data will be available by 2012. The ocean ecosystem has likely changed since the prewhaling era, making a return to prewhaling numbers infeasible; many marine ecologists argue that existing gray whale numbers in the eastern Pacific Ocean are approximately at the population’s carrying capacity. The gray whale became extinct in the North Atlantic in the 18th century Radiocarbon dating of subfossil or fossil European (Belgium, the Netherlands, Sweden, the United Kingdom) coastal remains confirms this, with whaling the possible cause. Remains dating from the Roman epoch were found in the Mediterranean during excavation of the antique harbor of Lattara near Montpellier in 1997, raising the question of whether Atlantic gray whales migrated up and down the coast of Europe to calve in the Mediterranean. Similarly, radiocarbon dating of American east coastal subfossil remains confirm gray whales existed at least through the 17th century. This population ranged at least from Southampton, New York, to Jupiter Island, Florida, the latest from 1675. In his 1835 history of Nantucket Island, Obed Macy wrote that in the early pre-1672 colony a whale of the kind called “scragg” entered the harbor and was pursued and killed by the settlers. A. B. Van Deinse points out that the “scrag whale”, described by P. Dudley in 1725 as one of the species hunted by the early New England whalers, was almost certainly the gray whale.
In mid-1980, there were three gray whale sightings in the eastern Beaufort Sea, placing them 585 kilometers (364 mi) further east than their known range at the time. In May 2010, a gray whale was sighted off the Mediterranean shore of Israel. It has been speculated that this whale crossed from the Pacific to the Atlantic via the Northwest Passage, since alternative routes through the Panama Canal or Cape Horn are not contiguous to the whale’s established territory. There has been gradual melting and recession of Arctic sea ice with extreme loss in 2007 rendering the Northwest Passage “fully navigable”. The same whale was sighted again on May 30, 2010, off the coast of Barcelona, Spain. In January 2011, a gray whale that had been tagged in the western population was tracked as far east as the eastern population range off the coast of British Columbia.