Blue whales occur widely in the world’s ocean and became a target of commercial whalers in what is termed the modern era of whaling. Largest populations occurred in the southern Hemisphere and the Antarctic blue whale was the most heavily hit by commercial whaling with close to 300,000 killed primarily in the first half of the 20th century. From a world-wide abundance of over 300,0000 their numbers are estimated at close to 10,000 now, more than 40 years after the supposed end of commercial whaling in 1966. One of the healthier populations of blue whales documented post-whaling is in the eastern North Pacific. There are thought to be at least a half dozen if not a dozen or more distinct populations of blue whales around the world (based in part on different song types as well as genetics). In the North Pacific, at least two populations exist based on these song types. The eastern North Pacific population we have been studying ranges at least from Central America to the south to the Gulf of Alaska in the north.
Cascadia Research has been studying eastern North Pacific blue whales since 1986 using photographic identification. Our catalog now contains over 2,000 individuals with distinct markings. Resightings of these identified whales have provided confirmation of movements of the blue whales off the US West Coast down to the Costa Rica Dome and up to Alaska. Our estimates of abundance based on mark-recapture calculations based on resightings of these photo-identified whales, have yielded an estimate of just over 2,000 for this eastern North Pacific population. While these initial estimates were higher than expected our data from the early 1990s to late 2009 have shown only a slight indication of an upward trends. Some other estimates of abundance from line-transect density estimates for the US West Coast have actually shown a decrease in numbers from the 1990s to the last 10 years. We think this discrepancy reflects that blue whales were dispersed more widely especially to the north in the last 10 years and that is why the density dropped even though the total population did not necessarily decrease.
Extensive research has been conducted on blue whales in a few key areas. This has included off the US West Coast (especially off southern California) in the summer and fall and also in the Sea of Cortez, Mexico in winter and spring. There have also been cruises to the Costa Rica Dome area both by Southwest Fisheries Science Center and two cruises Cascadia has participated in. While we know that the west coast of Baja is an important area for blue whales, relatively little work has been conducted there focused on blue whales.
The west coast of Baja was known as an important area for blue whales even in whaling days. One area where whaling was conducted in the early 1900s was based from a processor in Magdelena Bay off southwest side of Baja. Additionally, periodic surveys along the west coast of Baja have found high concentrations of blue whales. Satellite tags deployed on blue whales by Oregon State University have revealed the west coast of Baja as an important area in almost any time of year but especially winter and spring (Bailey et al. 2009). It is suspected blue whales are using these waters as a feeding areas.
Citation:
Calambokidis, J., S. Marin, and E. Vu. 2011. Baja blue whale research 2011: Summary of research conducted by Cascadia Research as part of an Oceanic Society Research Expedition with volunteers from Road Scholar. Unpublished report, 4 April 2011. 6pp.
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