By Mads Peter Heide-Jørgensen
The bowhead ecology project studies the habitat utilisation of bowhead whales at two spatial scales; the small scale in Disko Bay and the large scale covering the entire range of bowhead whales in Greenland and Canada. The methods that are used are:
- satellite tracking of individual whales with collection of positions and data on diving behavior
- collection of skin biopsies from bowhead whales
- collection of samples from local subsistence hunt of bowhead whales
- marine biological studies of the abundance and occurrence of important prey items for bowhead whales
The tracking data has now revealed where the bowhead whales from Disko Bay go when they leave the bay in June. Several concentration sites in northern Canada has been identified and the Hudson Strait is now clearly demonstrated to be the major wintering ground for bowhead whales from both Canada and Greenland. As a special treat in 2010 two bowheads instrumented with satellite transmitters have now completed a full annual cycle and are back in Disko Bay, closing the ‘missing link’ on how they return to Greenland from Canada. We are still tagging whales in the bay and have this year deployed 32 tags. This will also allow us to look at how the whales will react to the oil drilling west of Disko Island that is supposed to start in June.
A total of 500 skin biopsies from bowhead whales have been collected in Disko Bay since 2000 and these have shown a large scale sexual segregation of bowhead whales where Disko Bay is mainly visited by mature females without calves. Only about 20% are males. There are few between-year recaptures of whales indicating that it is indeed a large population that supplies Disko Bay with bowhead whales. Analyses of stock identity of whales from Canada and Greenland are in progress and the results suggest a single wide ranging and highly segregated stock.
Again in 2010 have we been able to succesfully collect samples from the local bowhead harvest, and this year two mature females were examined of which one was pregnant and the other resting with 8 previous pregnancies. Both were feeding exclusively on copepods.
The studies of the abundance and occurrence of the primary bowhead prey, the copepods, were assisted by some early winter data on diving behavior that we were able to collect in March. One whale was instrumented with a time-depth-recorder that was retrieved after a week in the southern part of the bay. The diving data showed that the bowhead was consistently targeting copepods at a depth of about 180 m, much deeper than the spring surface layer that bowheads in May have access to after the phytoplankton bloom.