Calambokidis, J., J. Barlow, J.K.B. Ford, T.E. Chandler, and A.B. Douglas. 2009. Insights into the population structure of blue whales in the eastern North Pacific from recent sightings and photographic identifications. Marine Mammal Science 25:816-832
full PDF. The definitive version is available at Wiley
and some of the figures from the ms are provided below. For details and
photographs regarding the sightings of blue whales in British Columbia in 2007
see press release issued in 2007.
Blue whales were widely
distributed in the North Pacific prior to the primary period of modern
commercial whaling in the early 1900s. Despite concentrations of blue whale
catches off British Columbia and in the Gulf of Alaska, there had been few
documented sightings in these areas since whaling for blue whales ended in 1965.
In contrast, large concentrations of blue whales have been documented off
California and Baja California and in the eastern tropical Pacific since the
1970s, but it was not known if these animals were part of the same population
that previously ranged into Alaskan waters. We document 15 blue whale sightings
off British Columbia and in the Gulf of Alaska made since 1997, and use
identification photographs to show that whales in these areas are currently part
of the California feeding population. We speculate that this may represent a
return to a migration pattern that has existed for earlier periods for eastern
North Pacific blue whale population. One
possible explanation for a shift in blue whale use is changes in prey driven by
changes in oceanographic conditions, including the Pacific Decadal Oscillation (PDO),
which coincides with some of the observed shifts in blue whale occurrence.
Locations of blue whale
identifications in British Columbia and Gulf of Alaska and where these
individuals were also seen off California.