09 March 2012

NORTHWEST PASSAGE OPENS FOR BOWHEAD WHALES

Bowhead whale. Via.
  
A new paper in Biology Letters reports on two satellite-tagged bowhead whales from different oceans meeting in the ice-free waters of the Northwest Passage in September 2010. 
  
One whale was from West Greenland. The other from Alaska. Their paths crossed in the Parry Channel in the Canadian Arctic Archipelago (maps, below). 
  
From the paper:
  
It is not known what attracted the whales to this area, given the region has relatively low marine production in autumn compared with other known bowhead whale feeding areas.
   
Bowhead whale bones on ceremonial ground, Point Hope, Alaska. Credit: rnoblin via Flickr.

This was not the first times whales from different waters have met in an ice-free Northwest Passage. From the paper:
  
During the commercial whaling period (i.e. pre-1900), several harpoon heads of Atlantic origin were discovered in bowhead whales harvested in the Chukchi Sea/western Arctic, but this information was largely dismissed as anecdotal by scientists. 
  
Further evidence appears in the genetic record:
  
Recent genetic studies compared DNA of whales from Foxe Basin, Canada to whales from Alaska and suggest genetic mixing, although results are based on a small sample size from a highly segregated population. The lack of genetic differentiation between whales in the Pacific and the Atlantic, acknowledging that samples are taken several thousand years apart, suggests that some exchange of individuals occurred between whales in Svalbard and Alaska
  
Credit: Mads Peter Heide-Jørgensen, et al. Biol Lett. DOI:100.1098/rsbl.2011.0731. 

The maps show the individual tracks of the two whales from late spring through early autumn. The inset map shows where they overlapped. From the paper:
  
The Northwest Passage with tracks of four bowhead whales and extent of sea ice with greater than 50% concentration (white fields). (a) Track of a whale tagged on 4 May 2002 in West Greenland and ice extent on 20 September 2002. (b) Track of a whale tagged in Alaska on 12 May 2006 and sea ice extent on 8 August 2006. (c) Track of a whale tagged on 24 May 2010 in Alaska, one tagged on 15 April 2010 in West Greenland, and sea ice extent on 14 September 2010. The insert shows the area where whales occurred together in 2010. The whale from Alaska was present in Viscount Melville Sound between 19 August and 18 September while the whale from Greenland was present from 11 to 28 September.
  
1980: Sea ice coverage 1 Nov-31 Jan. Credit: NASA Earth Observatory.
2012: Sea ice coverage 1 Nov-31 Jan. Red star marks approximately where the two whales met in 2010. Credit: NASA Earth Observatory.
These latest images posted by NASA's Earth Observatory give you a sense of how the passage has opened up in the last three decades for whales... and presumably for others too. I marked (red star) approximately where the two whales met in 2010.
  
The authors conclude:
  
Given recent rates of sea ice loss, climate change may eliminate geographical divisions between stocks of bowhead whales and open new areas that have not been inhabited by bowhead whales for millennia (e.g. North of Greenland and north of the Canadian Archipelago).
The documented movements of bowhead whales in the Northwest Passage are perhaps an early sign that other marine organisms have begun exchanges between the Pacific and the Atlantic Oceans across the Arctic. Some of these exchanges may be harder to detect than bowhead whales, but the ecological impacts could be more significant should the ice-free Arctic become a dispersal corridor between the two oceans.


Foxe Basin Bowhead Whales from Stephen Ambruzs on Vimeo.

The open-access  paper:
  
  • Mads Peter Heide-Jørgensen, Kristin L. Laidre, Lori T. Quakenbush, and John J. Citta. The Northwest Passage opens for bowhead whales. Biol Lett. DOI:10.1098/rsbl.2011.0731.
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