509 



Abstract — The abundance and popu- 

 lation density of cetaceans along the 

 U.S. west coast were estimated from 

 ship surveys conducted in the summer 

 and fall of 1991, 1993, 1996, 2001, 

 and 2005 by using multiple-covari- 

 ate, line-transect analyses. Overall, 

 approximately 556,000 cetaceans of 

 21 species were estimated to be in 

 the 1.141,800-km2 study area. Delphi- 

 noids (Delphinidae and Phocoenidae), 

 the most abundant group, numbered 

 -540,000 individuals. Abundance 

 in other taxonomic groups included 

 -5800 baleen whales (Mysticeti), 

 -7000 beaked whales (Ziphiidae), and 

 -3200 sperm whales (Physeteridae). 

 This study provides the longest time 

 series of abundance estimates that 

 includes all the cetacean species in 

 any marine ecosystem. These esti- 

 mates will be used to interpret the 

 impacts of human-caused mortality 

 (such as that documented in fish- 

 ery bycatch and that caused by ship 

 strikes and other means) and to evalu- 

 ate the ecological role of cetaceans in 

 the California Current ecosystem. 



Abundance and population density of cetaceans 

 in the California Current ecosystem 



Jay Barlow (contact author)' 

 Karin A. Forney^ 



Email address for J. Barlow: Jay.Barlow@noaa.gov 



' National Ocean and Atmosphenc Administration 

 Southwest Fisheries Science Center 

 8604 La Jolla Shores Dnve 

 La Jolla, California 92037 



2 NOAA Southwest Fisheries Science Center 

 110 Shaffer Road 

 Santa Cruz, California 95060 



Manuscript submitted 4 October 2006 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 27 June 2007 by the Scientific Editor. 



Fish. Bull. 105:509-526 (2007). 



Estimates of cetacean abundance, 

 biomass, and population density are 

 key to assessing the potential effects 

 of anthropogenic perturbations on 

 cetacean populations (Carretta et al., 

 2006) and in understanding the eco- 

 logical role of cetaceans in marine 

 ecosystems (Trites et al,, 1997), Along 

 the U.S. west coast, most cetacean 

 species are vulnerable as bycatch in 

 gillnet fisheries (Julian and Beeson, 

 1998: Carretta et al., 2005), and fish- 

 eries catch many of the same species 

 that cetaceans consume (Trites et al., 

 1997). Large whales also die from ship 

 strikes (Carretta et al., 2006). West 

 coast cetaceans may be affected by 

 anthropogenic sound (e.g., sonar, ship 

 noise, and seismic surveys) and cli- 

 mate change. There is little published 

 information on current abundance to 

 evaluate direct anthropogenic impacts 

 on cetacean species and to estimate 

 their resource needs. 



The abundance of cetaceans along 

 the U.S. west coast was previously es- 

 timated for some species in some ar- 

 eas, but most available estimates are 

 based on surveys that were conducted 

 16 to 30 years ago (Dohl et al., 1986; 

 Barlow, 1995). In addition, most esti- 

 mates are based only on surveys that 

 were conducted within 185 km of the 

 coast. There was only one survey (in 

 1991) in waters greater than 185 km 

 offshore of California, and there are 

 no published estimates of cetacean 

 abundance for far offshore waters of 

 Oregon or Washington. The lack of 

 recent estimates and the lack of es- 



timates for offshore waters represent 

 clear gaps in our knowledge of west 

 coast cetaceans. 



In this study, new estimates of 

 abundance were determined in order 

 to fill our gaps in knowledge about 

 cetaceans in the California Current 

 ecosystem. Line-transect methods 

 were used to analyze data collected 

 from Southwest Fisheries Science 

 Center (SWFSC) ship surveys in 

 1991, 1993, 1996, 2001, and 2005 

 off the U.S. west coast. A new mul- 

 tiple-covariate, line-transect approach 

 (Marques and Buckland, 2003) was 

 used to account for multiple factors 

 that affect the distance at which ce- 

 taceans can be seen in different con- 

 ditions. Because cetaceans dive and 

 can be missed by visual observers, 

 the probability of detecting a group 

 of cetaceans directly on the transect 

 line was estimated from observa- 

 tions made by independent observ- 

 ers on those 1991-2005 surveys and 

 from other sources. Observer-specific 

 corrections were applied to remove a 

 bias in estimating group sizes. These 

 results represent one of the most 

 comprehensive analyses of cetacean 

 abundance and density for any large 

 marine ecosystem. 



Materials and methods 



Survey 



Surveys in 1991, 1993, 1996, 2001, 

 and 2005 were conducted in summer 



