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Saturday, April 26, 2008

Assessing the Impacts of Climate Change on Arctic Marine Mammals

Special issue of

Ecological Applications

Volume 18, Issue sp2 (March 2008)

published by the Ecological Society of America

While the Earth’s climate has exhibited broad extremes over geologic time, there is general agreement that the effects of global warming ongoing now are accentuated in the Arctic, and that the rate of environmental change may be unprecedented. How marine mammals respond to environmental change depends on a species’ adaptability, given its natural history and the temporal and spatial scale of perturbation. Although loss of sea ice as a platform for polar bears to hunt and walrus to rest grabs news headlines, there has been no rigorous effort to investigate either climate change or environmental responses, including those by humans, at the ecological scale of Arctic marine mammals. Here, we attempt just such an investigation through a collection of papers drafted by specialists in a cross-section of disciplines.

Why this collection of papers?—As Arctic sea ice is diminished, ice-associated marine mammals will be affected directly and indirectly. The overall area of sea ice habitat will shrink, reducing the range of ice-obligate species (e.g., ringed seal and polar bear). Ice substrate for breeding and resting will be lost, as will seasonal proximity between ice and key bathymetric features such as shallow continental shelves. Ecological process of the Arctic will change in many ways, while human activities such as shipping and resource development in the region will likely increase. The relationship among marine mammals, indigenous hunters, commercial interests, and sea ice will be sharply altered.

Such conclusions may seem self-evident, but understanding the specific mechanisms by which climate change will affect Arctic marine mammals is important both for its own sake and for determining the extent to which conservation strategies can help prevent or mitigate any negative impacts. A thorough assessment of this topic, involving several perspectives and disciplines, will help identify the species, characteristics, and regions of greatest vulnerability.

Four papers set the stage for assessing current and future status of Arctic marine mammals with respect to climate change. Walsh reviews current climatological understanding, including model projections for the coming century. Harington describes the evolutionary history of Arctic marine mammals. Murray discusses what zooarchaeology teaches us about past distributions. O’Corry-Crowe uses molecular genetics to investigate past and current distributions and behaviors.

The next four papers cover the potential effects of climate change on various aspects of Arctic marine mammals’ natural history and ecology. Bluhm and Gradinger discuss productivity and prey. Laidre et al. consider habitats. Burek et al. describe body condition and health. Hovelsrud et al. review human interactions. Metcalf and Robards examine the case of walrus hunting in western Alaska.

Finally, two papers synthesize the findings of the preceding papers to assess overall impacts and resilience of marine mammals (Moore & Huntington) and the potential for conservation action (Ragen et al.). Taken together, the papers provide a multidisciplinary, authoritative summary of current knowledge to serve both as a baseline for future assessments and as the basis for action in research and in conservation.

Defining the Arctic and Arctic marine mammals.—Simple and satisfactory definitions of the Arctic are elusive. Astronomical, climatological, oceanographic, botanic, and other boundaries have their strengths and weaknesses. For our purposes, we consider the Arctic marine environment to be the region where sea ice is a dominant feature for a considerable part of the year. Our region therefore includes the Arctic Ocean proper as well as the Barents and Bering seas and Hudson and Baffin bays. The Sea of Okhotsk and the Norwegian, Greenlandic, and Icelandic seas share some characteristics and species with the Arctic but are not included in the core Arctic region for our purposes.

More pertinent than a geographical limit, however, is the question of which species should be
considered ‘‘Arctic’’ for our assessment. Many species visit the Arctic at various times or are found in proximity to sea ice at some point in their migrations or life cycle. Relatively few species actually require sea ice for their survival, though it appears to be preferred habitat for several. Some species are found year-round in the Arctic but also have separate stocks in more southerly locations. While any species list has an element of arbitrariness, we have chosen as ‘‘core species’’ for this assessment the seven that occupy the Arctic environment and for which at least some portion of the population is associated with sea ice year-round:

Bowhead whale (Balaena mysticetus)
Beluga, or white whale (Delphinapterus leucas)
Narwhal (Monodon monoceros)
Bearded seal (Erignathus barbatus)
Ringed seal (Phoca hispida)
Walrus (Odobenus rosmarus)
Polar bear (Ursus maritimus)

These species are considered in all papers, and a summary of habitat and range for each appears in Laidre et al. in this volume.

In addition, nine other species are seasonal or occasional migrants to the Arctic or have some
association with sea ice. These include the harp seal (Phoca groenlandica), hooded seal (Cystophora cristata), ribbon seal (Phoca fasciata), spotted seal (Phoca largha), gray whale (Eschrichtius robustus), killer whale (Orcinus orca), minke whale (Balaenoptera acutorostrata), fin whale (Balaenoptera physalus), and humpback whale (Megaptera novaeangliae). Discussion of these species has been included where they either shed light on the core species or where changes in the core Arctic region are expected to have a significant effect on any one of these species. The reader is directed to species accounts in natural history guides for additional background information.

Acknowledgments.—We thank the Marine Mammal Commission (USA) for supporting the
preparation and publication of this Special Issue. We also thank the reviewers of the papers in this collection for their encouragement and constructive criticism.

Guest Editors

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