Abundance estimates of humpback and blue whales off the US West Coast based on mark-recapture of photo-identified individuals through 2008

Citation

Calambokidis, J. 2009. Abundance estimates of humpback and blue whales off the US West Coast based on mark-recapture of photo-identified individuals through 2008. Report # PSRG-2009-07 to Pacific Scientific Review Group, San Diego, CA 3-5 November 2009.

Introduction

Humpback and blue whales are considered endangered and their populations were depleted by whaling throughout most of their range. Both species make seasonal migrations between low latitude areas in winter and high latitude areas in summer. Blue whales feed off California from May through November (Dohl et al. 1983) and migrate to waters off Mexico and Central America in winter and spring (Calambokidis et al. 1990, Stafford et al. 1999, Mate et al. 1999, Chandler et al. 1999). Photographic identification of blue whales has revealed that animals identified off California are part of an eastern North Pacific population of blue whales that ranges as far north as the Queen Charlotte Islands and the Gulf of Alaska (Calambokidis et al. 2009) and as far south as the Costa Rica Dome (Chandler et al. 1999).
Recent studies of humpback whales in the entire North Pacific conducted under the SPLASH project have revealed a complex population structure with high degree of site fidelity to specific feeding and wintering areas but without a one to one association between these areas (Calambokidis et al. 2008). Overall abundance of humpback whales in the North Pacific was growing at 4-7% per year and through 2006 numbered about 20,000 (Calambokidis et al. 2008, Barlow et al. Submitted).
Starting in the early 1990s, photo-ID of humpback and blue whales along the US West Coast has provided accurate estimates of abundance using capture-recapture methods (Calambokidis et al. 1990a, 1990b, Calambokidis and Barlow 2004). These have complimented density-based abundance estimates available from line-transect surveys conducted by SWFSC (Barlow 2009, Barlow and Forney 2007, Forney 2007, Calambokidis and Barlow 2004). While annual estimates of humpback whales have been obtained from mark-recapture, blue whale abundance has only been primarily possible when at least one representative sample was obtained from the periodic surveys by SWFSC systematically covering both inshore and offshore waters (Calambokidis and Barlow 2004).
The primary objectives of the research reported here was to obtain new estimates of humpback and blue whale abundance along the US west coast based on mark-recapture of photographically identified individuals and examine trends in abundance.

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