U.S. Fish and Wildlife Service Reports on Pacific Walrus and Polar Bear Stocks in Alaska

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The U.S. Fish and Wildlife Service (FWS) on Wednesday (30 December 2009) released stock assessment reports for the Pacific Walrus and polar bears in Alaska.  The reports note the growing impacts of climate change on both species.

In a Federal Register notice (Marine Mammal Protection Act; Stock Assessment Report [PDF]), the FWS announced publication of a report on the Alaska stock of walruses; and two other reports on the status of polar bears.  The notice also responded to a series of questions raised during an earlier public comment period for previous drafts of the reports.

The Pacific Walrus in Alaska

The FWS presently is reviewing the status of the walrus under the Endangered Species Act, because it has found that listing of the walrus under the act may be warranted.  The review, initiated in October 2009, will produce a finding by 1 September of 2010. 

The information in the report is not reassuring.  According to the FWS, the "size of the Pacific walrus population has never been known with certainty."  The most recent population estimated cited by the report is for 2006 -- before the dramatic decline in Arctic Sea Ice in 2007 and subsequently.  Furthermore, the report says that "[i]mpacts to walrus of changes in arctic and subarctic ice dynamics are not well understood."  The report continues (references omitted):

Walrus are dependent on sea ice as a substrate for birthing, nursing, and resting between foraging trips. Annual winter ice in the Bering Sea
is predicted to decrease in extent by 40% by the year 2050. Summer sea-ice extent in the Chukchi Sea has decreased rapidly in recent years, retreating off the shallow continental shelf and over deep Arctic Ocean waters where walruses presumably can not feed. Declines in sea-ice extent, duration, and thickness are expected to continue

Some impacts of the loss of summer sea ice on walrus have been documented. Over the past decade, the number of walrus coming to shore along the coastline of the Chukchi Sea in Russia has increased. Female and young walrus are arriving earlier and staying longer at coastal haulouts as summer ice disappears. Numbers in the tens of thousands have been reported anecdotally from some haulouts in Chukotka. In fall of 2007 and 2009, large walrus aggregations were also observed along the Alaska coast. The ability of the food supply within foraging range of coastal haulouts to support large numbers of walruses over the long term is unknown. Thin walrus that appear to be physiologically stressed have also been reported from Chukotka. Walrus at dense coastal haulouts are vulnerable to disturbance, which can result in increased mortality from stampedes.

Limited subsistence hunting (or "harvesting") of the walruses is permitted, but the report notes that harvest levels far exceed sustainable levels and the "[i]mpacts of climate change on subsistence harvests of walrus are also difficult to predict."  It concludes that "[e]nsuring that harvest levels remain sustainable is a goal shared by subsistence hunters and resource managers in the U.S. and Russia. Achieving this management goal will require continued investments in co-management relationships, harvest monitoring programs, international coordination, and research."

See our posting, Dramatic Footage Shows Consequences for Walruses as Arctic Warms (2 October 2009).

Polar Bears in Alaska

Unlike the walrus, polar bears in Alaska already are listed under the ESA.  In the Chukchi/Bering and Southern Beaufort seas, polar bears are listed as threatened.   For both stocks, the primary concerns are habitat loss associated with climate change along with "potential overharvest," industrial activity and other human activities.

Both reports say:

Polar bears evolved over thousands of years to life in a sea ice environment. They depend on the sea ice-dominated ecosystem to support essential life functions. Sea ice provides a platform for hunting and feeding, for seeking mates and breeding, for movement to terrestrial maternity denning areas and occasionally for maternity denning, for resting, and for long-distance movements. The sea ice ecosystem supports ringed seals, the primary prey for polar bears, and other marine mammals that are also part of their prey base. 

Sea ice is rapidly diminishing throughout the Arctic and large declines in optimal polar bear habitat have occurred in the Southern Beaufort and Chukchi Seas between the two time periods, 1985–1995 and 1996–2006. In addition, it is predicted that the greatest declines in 21st century optimal polar bear habitat will occur in Chukchi and Southern Beaufort Seas. Patterns of increased temperatures, earlier onset of and longer melting periods, later onset of freeze-up, increased rain-on-snow events, and potential reductions in snowfall are occurring. In addition, positive feedback systems (i.e., the sea-ice albedo feedback mechanism) and naturally occurring events, such as warm water intrusion into the Arctic and changing atmospheric wind patterns, can operate to amplify the effects of these phenomena. As a result, there is fragmentation of sea ice, a dramatic increase in the extent of open water areas seasonally, reduction in the extent and area of sea ice in all seasons, retraction of sea ice away from productive continental shelf areas throughout the polar basin, reduction of the amount of heavier and more stable multi-year ice, and declining thickness and quality of shore-fast ice .

The Chukchi/Bering seas and the Southern Beaufort Sea population stocks are currently experiencing the initial effects of changes in sea ice conditions. These populations are vulnerable to large-scale dramatic seasonal fluctuations in ice movements, decreased abundance and access to prey, and increased energetic costs of hunting."

Learn more about polar bears.

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