Changing Arctic Sea Ice Patterns affect Movements and Habitats of Marine Mammals
| Marilyn Sigman, Alaska SeaGrant/MAP
Tags: Bowhead Whale, Gray Whale, Warlus, Arctic Ocean, Climate Change, Changing Arctic Sea Ice, Arctic Ocean, Alaska Marine Ecosystems, Marine Ecosystem Science
NOAA scientist Sue Moore reported at the 2010 Alaska Marine Science Symposium on a study that related the changes in Arctic sea ice extent with the movements and habitats of polar bears, walruses, and gray whales in the Pacific side of the Arctic region. During 2007-2009, September ice extent was 35% below normal with the major loss occurring on the Pacific side.
Autumn 2009 had an unprecedented low freeze-up rate. Polar bears were forced onshore or to ice over relatively unproductive deep water in the Arctic basin where seals may not have been accessible. Walruses hauled out in unprecedented numbers on land, resulting in trampling of calves and changes in foraging behaviors. The southbound migration has been delayed when freeze-up is later. A number of gray whales overwintered north of Barrow in 2003-2004 and they now routinely feed in the same areas with bowhead whales from late summer through autumn, a phenomenon not seen since the 1980’s.
Moore and her co-authors James Overland, NOAA, and Chad Jay, USGS, described the marine mammals as ecosystem sentinels and called attention to the likelihood that the effect of a warming Arctic would be different for ice-dependent and ice-associated species compared to the seasonally migrant whales. In particular, the effect on the whales was unpredictable and would depend on changes in their plankton prey which could increase as a result of stronger currents or novel species thriving in warmer water. In addition to changes in the ecosystem, marine mammals will have to contend with increased human activity in the Arctic.
A number of other studies focused on bowhead whales. Moore was a co-author on a presentation about using historical aerial photographs of muddy bowhead whales to study the amount of feeding on bottom-dwelling or epibenthic organisms such as amphipods. Woods Hole scientist Carin Ashjian headed up a study of the variability of ocean biology at a bowhead whale feeding hotspot on the Continental Shelf to the northwest of Barrow, Alaska, from 2005-2009.
The oceanographic conditions where water masses from the Pacific, Bering Sea, and Arctic Ocean come together produces the hot spot during the fall as the whales migrate from the Arctic Ocean to the Bering Sea. The year-to-year variability is related to the extent and location of sea ice and ocean temperatures in surface waters. Both 2005 and 2007 were characterized by little or no sea ice and warm surface and Pacific-origin water (approximately 11 degrees C.). In 2006, 2008, and 2009; less water from the Pacific, and melting sea ice in 2006, contributed to colder surface waters (less than 4 degrees C.).
The direction and strength of the wind combined with the currents are important in shorter-term variability in zooplankton abundance and species in the large concentrations of prey required by the bowheads. In 2009, the abundance of euphasiids, or krill, transported from the Bering Sea, increased dramatically.
For more background on this study which has involved whaling captains, oceanographers, and whale biologists, see the March 2009 report Interannual Variability in Physical-Biological Properties on the Shelf near Barrow, Alaska by Carin J. Ashjian. The report includes a graphic, “Winds, Currents, and Krill: the story of the Barrow Area Bowhead Whale Feeding Hotspot.”
The story compares the situations of when east winds blow and when the winds are weak or stop altogether. When east winds blow, the currents carry krill through the Barrow Canyon into the Beaufort Sea beneath the relatively warm Alaska Coastal Water mass. The winds from the east move the Alaskan Coastal water farther away from the coast and krill in bottom waters are upwelled into shallow Continental Shelf waters. The krill are then transported to the west around Barrow. When winds are weak or stop altogether, upwelling currents stop and warm Alaska Coastal current water move close to shore.
The Alaska Coastal current water extends down to the bottom and acts as a barrier to the movement of the krill. The krill carried westward by the currents when the winds were from the east are prevented from escaping into deeper water by the Alaska Coastal Current so they collect in large numbers around Point Barrow. The bowhead whales feed on the dense patches of krill during late summer and during their annual migration westward during the fall feeding migration.
A related monitoring effort conducted by oil industry observers led by LGL Alaska Research Associates scientist Dale Funk reported the use of land for haul-outs along the Alaska Chukchi Sea coast. Prior to 2007, few cases of terrestrial haul-out sites had been documented. The summer of 2007 had the lowest Arctic sea ice extent ever recorded.
During late summer, 2007, the scientists used observers on boats, aerial surveys, and acoustic recorders on the seafloor to locate and document 16 terrestrial haul-out sites with approximately 3,000 walruses between Point Hope and Barrow. 2007 More than 1,000 walruses were also encountered in open water by observers on boats. Based on acoustic recordings near Pt. Lay, the walrus began hauling out on land as early as August 10. Aerial surveys began on August 25 and continued to document large numbers of walrus on land through early October.
It appears that walrus abandoned the ice floes that remained after the ice retreated which were well north of their normal feeding areas in the Chukchi Sea. Walrus use of terrestrial haul-outs was not detected by similar industry monitoring efforts in 2006 and 2008.
Sue Moore co-authored a journal article with Henry Huntington that was published in Ecological Applications in 2008. Arctic Mammals and Climate Change: impacts and resilience provides resilience scenarios for the three ice-related species categories relative to four regions defined by projections of sea ice reductions by 2050.
According to the abstract, "resilience scenarios suggest that:
Link to 2010 Alaska Marine Science Symposium Abstracts
- some populations of ice-obligate marine mammals will survive in two regions with sea ice refugia, while other stocks may adapt to ice-free coastal habitats
- ice-associated species may find suitable feeding opportunities within the two regions with sea ice refugia and, if capable of shifting among available prey, may benefit from extended foraging periods in formerly ice-covered seas, but
- they may face increasing competition from seasonally migrant species, which will likely infiltrate Arctic habitats. The means to track and assess Arctic ecosystem change using sentinel marine mammal species are suggested to offer a framework for scientific investigation and responsible resource management."
Marine Mammals and Sea Ice Loss in the Pacific Arctic
Sue E. Moore, NOAA
James E. Overland, NOAA
Chadwick V. Jay, USGS
Evidence of Feeding by Bowhead Whales from Aerial Photography
Julie A. Mocklin, firstname.lastname@example.org, NOAA
David J. Rugh, email@example.com, NOAA
Sue E. Moore, firstname.lastname@example.org, NOAA
Year to year variability of ocean biology at a bowhead whale feeding hotspot near Barrow, AK: 2005-2009
Carin J. Ashjian, Woods Hole Oceanographic Institution
Robert G. Campbell, University of Rhode Island
Stephen R. Okkonen, University of Alaska Fairbanks
Barry F. Sherr, Oregon State University
Evelyn B. Sherr, Oregon State University
Pacific walrus movements and use of terrestrial haul-out sites along the Alaskan Chukchi Sea coast 2006-2008
Dale W. Funk, LGL Alaska Research Associates, Inc
Tannis A. Thomas, LGL Limited, environmental research associates
William R. Koski, LGL Limited, environmental research associates,
Darren S. Ireland, LGL Alaska Research Associates Inc
Marjo Laurinolli, JASCO Applied Science
A. Michael Macrander, Shell Exploration and Production Company