Friday, 9 March 2012

Bowhead Whales in the Northwest Passage.

The Bowhead Whale (Balaena mysticetus) is a large (20 m, 75-100 tonnes) filter-feeding whale with an Arctic Distribution. It is found in both the Pacific and Atlantic Oceans with very little genetic variation between the two areas, although the populations are generally thought to be kept separate by the Arctic pack ice. Skeletons found in Coronation Gulf, between Victoria Island to the north and North America to the south, suggest that in the Early Holocene, 11 000-8500 years ago, Bowhead Whales were able to utilize the Northwest Passage between the Atlantic and the Pacific.

Bowhead Whale (Balaena mysticetus). Oregon State University.

In a paper published in the journal Biology Letters on 21 September 2011, a team of scientists led by Mads Peter Heide-Jørgensen of the Greenland Institute of Natural Resources, describe the results of a ten year study of Bowhead Whales using radio-tagging equipment, which suggests that modern Bowhead Whales may also be able to use the Northwest Passage.

The team first observed a sub-adult whale entering the eastern end of the Passage from Baffin Bay in 2002, but this whale stayed less than two weeks before returning to the Bay.

(a) The path taken by a young whale that entered the eastern end of the Northwest Passage in 2002. Ice pack is shown as it was on 20 September 2002. From Heide-Jørgensen et al. (2011).

After this no tagged whales entered the Passage for several years, then in 2006 an adult whale entered the Passage from the Alaskan end, spending five months in the Passage and coming within 800 km of the area reached by the 2002 whale; the opposite end of the ice pack blocking the central Passage.

Then in 2010 two whales were recorded entering the Passage, one from each end. This year the ice pack in the central Northwest Passage had completely melted, allowing the two whales to move into the same area and cross paths on several occasions, before returning to their home oceans.

(b) The path taken by a single whale from the Alaskan side of the Passage in 2006. (c) The paths taken by a pair of whales that entered the Passage from opposite ends in 2010. From Heide-Jørgensen et al. (2011).

This suggests that the whales are aware of the Northwest Passage, and are willing to use it should the opportunity arise. It is highly likely that global warming will lead to more summers when the passage completely opens, and that this will lead to a greater intermingling of whale populations (and other marine organisms) from both sides of the Arctic. It is also likely that the whales have utilized the Passage previously in other warm climatic periods, such as the Medieval Climate Optimum, between about 950 and 1100 AD, when temperatures were cooler than they are now, but warm enough that the Northwest Passage may have had occasional open years.

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