Tracking of blue whales by satellite over a 15-year period off the U.S. West Coast suggests that the whales consistently return to feed in specific locations each year, according to a study published July 23, 2014 in the open-access journal PLOS ONE by Ladd Irvine from Oregon State University and colleagues. These data may be used to mitigate human threats to the whale population.
The endangered blue whale population has been slow to recover since the establishment of protections in the mid-1960s. Scientists suggest that one reason for this slow recovery may be ship strikes that injure or even kill whales. To better understand where important whale habitat and shipping lanes overlap along the U.S. West Coast, scientists attached satellite tags to 171 whales off the coast of California during summer and early fall from 1993 to 2008. The authors analyzed the whales' paths within 200 nautical miles of the coast, and based on their distribution identified areas of highest usage by the whales.
Travel distance and ranges of individual whales varied dramatically, but blue whales consistently used similar feeding grounds each year despite different ocean conditions, like El Niño and La Niña. The two most heavily used areas were in the Gulf of the Farallones, off central California, and the western part of the Channel Islands in southern California. The authors suggest the individual variation in range size may represent different feeding strategies for individuals. Additionally, the authors found that tagged whales generally departed U.S. waters from mid-October to mid-November and they tended to occupy the more northerly portion of the range during the latter part of the feeding season. The authors report a high overlap between the areas heavily used by tagged blue whales and busy shipping lanes leading to major U.S. ports, and suggest possible modifications to ship routing aimed at reducing the likelihood of collisions with whales.
Ladd Irvine added, "We found that the two areas of highest use by tagged blue whales off the U.S. West Coast during the summer and fall are crossed by busy shipping lanes leading to major ports. This information may be used to help mitigate human threats to the blue whale population."
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Citation: Irvine LM, Mate BR, Winsor MH, Palacios DM, Bograd SJ, et al. (2014) Spatial and Temporal Occurrence of Blue Whales off the U.S. West Coast, with Implications for Management. PLoS ONE 9(7): e102959. doi:10.1371/journal.pone.0102959
Funding: Funding: Funding for this research was provided by a variety of sources across 15 years including the Office of Naval Research, Tagging of Pacific Pelagics, the National Science Foundation , the Oregon State University Marine Mammal Institute Endowment, the Alfred P. Sloan Foundation , the Packard Foundation, and National Geographic. Funding was also provided under the interagency NASA, USGS, National Park Service, US Fish and Wildlife Service, Smithsonian Institution Climate and Biological Response program, Grant Number NNX11AP71G. While a number of the authors are employed by the Oregon State University Marine Mammal Institute, funding by the Marine Mammal Institute Endowment of some of the work presented here (typically in the form of matching funds) did not influence study design, data collection and analysis, decision to publish, or preparation of this manuscript. None of the other funding agencies influenced any aspects of this manuscript.
Competing Interest: Steven Bograd is currently an editor for this journal and is an author on this paper. This does not alter the authors' adherence to PLOS ONE Editorial policies and criteria.