Blue whales are thought to be among the most endangered of the great whales. Scientists estimate that the whaling industry destroyed 97 percent of the world's population. Over 360,000 blue whales were killed in the Antarctic alone. Antarctic blue whales continue to be one of the most depleted populations of whales in the world, with an estimated 2,280 remaining today, or less than 1% of pre-exploitation levels (Branch 2008).
Eastern North Pacific Blue Whales
The largest remnant group of blue whales in the world may feed off the California coast during the summer. This group, called the eastern North Pacific population, is estimated to number just under 1,200 individuals (NOAA Stock Assessment Report, 2007). The whales in this population migrate between feeding areas along the west coast of the United States and Canada and breeding and calving grounds off Mexico and Central America. The exact locations of the breeding and calving grounds remain unknown.
Beginning in 1993, the OSU Marine Mammal Institute has tagged 184 blue whales from this eastern North Pacific population, in an effort to more fully understand their critical habitat requirements, migration routes and destinations, seasonal movements, and diving behavior. Surface-mounted tags capable of recording the duration and depth of blue whale dives have been used (Lagerquist et al. 2000), as well as semi-implantable tags providing long-term location information
The results of our 1994 and 1995 studies led to the first long-term tracks of blue whales (up to 78 days), providing the first migratory route information for this species as well as documenting a link between blue whales feeding off California and those seen in the Eastern Tropical Pacific (ETP, Mate et al. 1999). Dive habit information showed changes in diving and respiratory characteristics depending on time of day, behavior, and water depth.
Satellite-monitored radio tracklines of blue whales tagged off California in 1994 and 1995. Each color represents a different whale.
The link between blue whales feeding off southern California and the ETP was reinforced during subsequent years, when blue whales were tracked from California to the Costa Rica Dome, where they remained for the winter. The Gulf of California was also identified as a wintering ground for this population, after 5 whales tagged in 1999 spent the winter there. Two tags from a study in the fall of 2000 continued to transmit for nine months, allowing the whales’ northward migration into U.S. waters to be recorded. A blue whale tagged in the Gulf of California in the spring of 2002 did not migrate to California during its tracking period (6.5 months), demonstrating that not all whales leave Mexican waters during the summer. The knowledge that not all eastern Pacific blue whales travel into U.S. waters in the summer is critical when interpreting abundance estimates from ship surveys conducted off the California, Oregon, and Washington coast during the summer.
Beginning in 2004, further information has been provided on migration routes and feeding ground movements for this population through our work with the TOPP Program (Tagging of Pacific Pelagics), co-funded by the Sloan, Packard and Gordon Moore Foundations. Each summer, from 2004-2008, we have taken our research vessel, the R/V Pacific Storm, from Oregon to California to study blue, fin, and humpback whales as part of this program. Seventy-four blue whales have been tagged during this time, one of these providing a record tracking period of up to 504 days.
As with previous years’ studies, tagged blue whales showed a great deal of individual variation in their movements, with some remaining in coastal waters, and others traveling as far as 2000 km from shore. While some animals headed south to Mexico, others moved north to Oregon and British Columbia. One animal spent almost 2 months in the Gulf of Alaska, confirming blue whale presence in this area in the fall. Annual variation in both feeding ground movements and migratory destinations was also evident, likely due to changes in oceanographic conditions from year to year. For example, blue whales tagged in 2005 were distributed farther offshore than those tagged in 2004, likely as a result of decreased productivity in the nearshore waters from El Nino-like conditions off California and Oregon in the spring and summer of 2005.
Similarities in blue whale movements from year to year were also evident, particularly the consistent use of areas off the west coast of Baja California and the Channel Islands in southern California, demonstrating that persistent oceanographic features are an important element in their seasonal distribution (Fiedler et al. 1998, Etnoyer et al. 2004, Etnoyer et al. 2006).
For real-time tracking information on tagged blue whales, check out the TOPP website.
Southern Hemisphere Blue Whales
In January 2004, five tags were placed on blue whales in the fjords of southern Chile, providing the first tracking data on a Southern Hemisphere blue whale population. The whales stayed in the feeding areas longer than was expected, mainly hugging the nearshore areas, with occasional forays out of the fjords into the open ocean. Two of the whales went north and offshore to the Nazca Ridge (approximately 500 miles from shore, 25 degrees south latitude), where colliding tectonic plates are building up an underwater ridge. The upwelling is excellent in this area, and where there’s upwelling, there are usually good food resources. It may be that the Nazca Ridge is a winter feeding area for this population.
