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Coldest Habitat

The Bowhead whale range is restricted to the Arctic ice-bound seas (Braham, 1984). It spends all year in this unique habitat, unlike other Balaenidae that migrate to tropical waters to rear their young, therefore Bowheads are uniquely adapted to survive in this extreme habitat. The Arctic incorporates the Arctic Ocean and lands of Greenland, Svalbard, Baffin Islands, Iceland, small northern islands and northern parts of Europe, Canada, Alaska and Russia (Figure 2) (Braham et al., 1980). Due to the surrounding lands Bowhead whales are constantly threatened by many human activities. Their direct human threat is native whale hunters that live in the Arctic region and use whales for traditional purposes. Bowheads have been an important marine resource for Inuit survival for centuries (Braham, 1984, Best, 2001).

Arctic map

Figure 2: Map of the Arctic region. The Arctic Ocean winter ice extent is illustrated by the darker blue of the ocean and the summer ice extent is the white area. The isotherm encircling with radial latitude of 23° 28’ is the circular latitudinal line around the Arctic.

The Arctic ice cap is an isotherm (circular line where all the points connected by it have same average temperature over a given period) encircling with radial latitude of 23° 28’(Blix, 2005). At winter solstice (no solar radiation input) temperatures falls to -50°C and at summer solstice (continuous solar radiation) the temperature is rarely above 0°C due to the albedo effect (89-90% of radiation is reflected off the icy surface) and the systemic winds (Blix, 2005). In summer the sea ice melts, resulting in sea ice retraction.  Another important environmental factor is the Arctic surface water circulation of nutrients and isotherm climate. The surface currents are the Beaufort Gyre and the Transpolar Drift (Figure 3) (Blix, 2005). These physical factors are vital for maintaining constant ice cover all year and supporting and providing suitable habitat for primary productivity (ice algae and diatom growth) which is fundamental to the arctic ecosystem. Sea ice also provides a safe environment for seal breeding and protection from Killer Whale predation on Bowhead calves (Berta et al., 2005, George et al., 2004). These physical characteristics are also essential for Bowhead migration and survival as they break up the ice, creating polynyas (areas of open water surrounded by ice) (used for breathing holes, protection and an abundant food resource), reducing ice thickness and creating leads (channels in the ice) used by Bowheads for breathing (George et al., 2004, Carrol and Smithhisler, 1980, Stirling, 1980).  Climate change is at present one of the greatest threats to the survival of Bowhead and other Arctic organisms with loss of habitat and food resources (Moore and Laidre, 2006).

Sea  ice cover in September and March and the major surface currents governing the transport of sea ice. The numbered lines show the expected time in years for the ice at that location to exit the Arctic Ocean through the Fram Strait (Anon, 1997)  Image originates fromBlix, AS. (2005)  Arctic Animals and their adaptations of life on the edge. Book

Figure 3: Sea ice cover in September and March and the major surface currents governing the transport of sea ice. The numbered lines show the expected time in years for the ice at that location to exit the Arctic Ocean through the Fram Strait. (Source: Blix 2005)

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