Photographic identification of humpback and blue whales off the US West Coast: Results and updated abundance estimates from 2008 field season

Citation

Calambokidis, J., E. Falcone, A. Douglas, L. Schlender, and J. Huggins. 2009. Photographic identification of humpback and blue whales off the US West Coast: Results and updated abundance estimates from 2008 field season. Final Report for contract AB133F08SE2786 from Southwest Fisheries Science Center, La Jolla, CA.

Abstract

Photographic identification of humpback and blue whales was conducted along the US West Coast in 2008 for the primary purposes of generating updated abundance estimates of both species using mark-recapture. We conducted 66 days of dedicated and opportunistic photo identification surveys off California, Oregon, and Washington primarily between June and November 2008. Additional photographic identifications were obtained by collaborating researchers and naturalists including those working from whale watch boats in areas like the Santa Barbara Channel and Monterey Bay. For all of the US West Coast, 808 identifications were made of 497 unique humpback whales which represented the largest number of individuals identified in any year of research so far along the US West Coast. A total of 437 identifications of 216 unique blue whales were made along the West Coast with almost half of these from the Santa Barbara Channel. Petersen mark-recapture estimates for humpback whales off California-Oregon yielded estimates for 2007-2008 of 2,043 (CV=0.10) humpback whales, the largest we have obtained to date consistent with an 8% annual rate of increase, although trends for the last 10 years have been more erratic largely due to our sample representing a decreasing proportion of this growing population leading to greater variation and possibly greater susceptibility to biasing factors. Estimates of humpback whales off Washington, a feeding aggregation relatively distinct from California-Oregon, were more variable but in the range of 500 animals. Blue whale photographic identifications from 2005 to 2008 were pooled to generate a single improved abundance estimated based on identifications from systematic surveys in 2005 and 2008 conducted by SWFSC as the unbiased sample and all other identifications as the 2nd independent sample. This pooled sample yielded an improved abundance estimate of 2,497 (versus the previous 2,842) with a tighter CV than had been possible previously. This estimate is slightly higher than the mark-recapture estimates of about 2,000 from the 1990s and may reflect a slight increase in blue whale abundance. These estimates are in contrast to the sharp decline in estimates of blue whales in this region from line-transect estimates since the 1990s. This discrepancy between the two methods appears to be the result of blue whales expanding their distribution since the 1990s and only being present part of the time off the US West Coast lowering the average density present (but not reflecting an actual population decline).

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