While the physical changes in the Arctic environment associated with climate change, such as reduced ice cover and loss of multi-year ice, are well documented, the biological impacts of these changes are not as well understood. There are indications that formerly sub Arctic species of mid trophic organisms (primarily zooplankton and fish) are extending their ranges northward and the introduction of these may disrupt the direct linkage between primary production and the rich benthic communities that have historically been the primary prey base for gray whales.
Since the early 1990s, there has been a general northward shift in the primary feeding grounds for gray whales from the previously rich benthic communities of the Chirikov Basin into the Chukchi Sea. Now large aggregations of gray whales have become a nuisance to native hunters out of Barrow, Alaska who are in pursuit of bowhead whales. How much of this shift in feeding behavior is the result of the slow warming of the Arctic environment and how much is caused by over grazing of benthic communities by a large gray whale population is still a matter of debate.
What is clear is that gray whales have increased the amount of time they spend feeding far north of the Bering Straits. In addition the timing of their southbound migration is occurring later and there is a strong link between the timing of the melt of seasonal ice in the Bering Sea and the number of calves counted in the following spring. There have also been more observations of “skinny whales” in the lagoons and along the Pacific Coast, but it is difficult to determine how much of this is the result of more sensitivity of scientists and the public to gray whale condition following the unusual mortality event of 1999 and 2000.
Figure 1. Historic primary feeding grounds for eastern North Pacific gray whales
Perryman, W., Donahue, M., Perkins, P., and S. Reilly. 2002. Gray whale calf production 1994-2000: Are observed fluctuations related to changes in seasonal ice cover? Marine Mammal Science, 18(1):121-144.
Moore, S.E. 2008. Marine Mammals as Ecosystem Sentinels. Journal of Mammalogy. 89(3)000-000.
Moore, S.E., Grebmeier, J.M. and Davies, J.R. 2003. Gray whale distribution relative to forage habitat in the northern Bering Sea: current conditions and retrospective summary. Canadian Journal of Zoology. 81:734-742.