Research on humpback and blue whales off California, Oregon, and Washington in 2001
Calambokidis, J., T. Chandler, L. Schlender, K. Rasmussen, and G.H. Steiger. 2002. Research on humpback and blue whales off California, Oregon, and Washington in 2001. Final report to Southwest Fisheries Science Center, La Jolla, CA. Cascadia Research, 218½ W Fourth Ave., Olympia, WA 98501. 50pp
Cascadia Research conducted research on humpback and blue whales off California, Oregon, and Washington in 2001. The primary purpose of the research has been to examine distribution, abundance, movements, and population dynamics of humpback and blue whales in the eastern North Pacific using photographic identification of individual animals.
Photographic identification was primarily conducted from small boats on 63 days of totaling 522 hours on the water. Additional, photo-ID was conducted from SWFSC’s ORCAWALE cruise off California, Oregon, and Washington, during surveys based from the Scripps vessel Sproul, and opportunistically from whale-watch boats. Suitable identification photographs of blue whales were made on 539 occasions representing 274 unique whales, one of our highest annual totals. Identifications of humpback whales were made on 541 occasions representing 311 unique individuals.
Estimates of humpback whale abundance using a number of mark-recapture models indicated abundance had declined starting in the late 1990s. After a high of just over 1000 whales in the late 1990s, the current estimate shoes a decline to 779 whales. The reduction appears to have occurred as a result of an elevated mortality (or emigration) rate. There has not been any indication of decreased number of calves in the population or increased number of strandings. The cause for this decline is not clear but appears to coincide with the timing of the severe 199798 El Nino. While the population does not appear to have recovered to pre-whaling numbers, there have been indications of declines in plankton and zooplankton-feeding seabirds off California in the 1980s and 1990s and may be lowering the carrying capacity for humpback whales.
Blue whale abundances could not be accurately estimated from the 2001 samples because relatively few blue whales were encountered and identified during the systematic SWFSC surveys. The identifications from these surveys provide an essential representative sample of blue whales in both inshore and offshore waters. Estimates made using the 2001 data yielded an abundance of only about 1,000 blue whales, well below the numbers estimated obtained from previous surveys. The small number of identifications obtained from the 2001 systematic surveys, however, result in these estimates having a high level of imprecision.
Tagging efforts in 2001 resulted in successful suction-cup attachment of two types of tags on blue whales. Crittercam deployments yielded information on feeding and diving behavior of blue whales off southern California. Data and video images from these deployments of San Miguel and San Nicolas Island showed blue whales feeding down to 300 m on extremely dense layers of krill. Additional short test deployments were made of a new acoustic-recording tag.