Updated Analysis of Abundance and Population Structure of Seasonal Gray Whales in the Pacific Northwest, 1998-2010

The existence of a small number of Eastern North Pacific gray whales that spend the spring, summer and fall feeding in coastal waters of the Pacific Northwest has been known for some time and localized short-term studies have examined aspects of the natural history of these animals. We report the results of a 13-year (1998- 2010) collaborative study examining the abundance and the population structure of these animals conducted over a number of regions from Northern California to British Columbia using photographic identification. Some 14686 identifications representing 1031 unique gray whales were obtained. Gray whales seen after 1 June (after the northward migration) were more likely to be seen repeatedly and in multiple regions and years and therefore 1 June was used as the seasonal start date for the data included in the abundance estimates. Gray whales using the Pacific Northwest in summer and fall include two groups: 1) whales that return frequently and account for the majority of the sightings and 2) apparent stragglers from the migration seen in only one year, generally for shorter periods and in more limited areas. Abundance estimates for whales present in summer and fall using four different methods over different geographic scales revealed the abundance of animals to be at most a few hundred individuals. All of the estimators except those based on Lincoln-Petersen, which was likely biased by the violation of population closure, showed an increase in abundance in the late 1990s and early 2000s. This was during the period the eastern North Pacific gray whale population was experiencing a high mortality event and this created an apparent influx of animals into the area. While estimates during that period may have been altered by this event, the abundance since then has been very stable. Recent matches of photo-identified gray whales from the Pacific Northwest to other regions have provided new insights into the movement of some of these individuals including matches to Barrow, Alaska. The proportion of calves documented was generally low but varied dramatically among years and may have been biased downward by weaning of calves prior to entry in the study area or prior to much of the collaborative seasonal effort. Observations of calves returning to the Pacific Northwest in subsequent years documents one possible mechanism for recruitment. The results we present will be valuable in assessing the impacts of potential resumption of a gray whale hunt by the Makah Tribe.


Calambokidis, J., J.L. Laake, and A. Klimek. 2012. Updated Analysis of Abundance and Population Structure of Seasonal Gray Whales in the Pacific Northwest, 1998-2010. Paper SC/M12/AWMP2-Rev submitted to the International Whaling Commission Scientific Committee.

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