Barlow. Abundance of cetaceans in California waters: ship surveys 



Species identification 



Observers attempted to classify all the species 

 present in a group to the lowest possible taxonomic 

 level (one member of each team was a cetacean iden- 

 tification expert with at least nine months of at-sea 

 survey experience on prior marine mammal surveys). 

 Several higher taxonomic groups were used in cases 

 where species identification was not possible. These 

 higher groups were beaked whales of the genus 

 Mesoplodon; unidentified sei or Bryde's whales; uni- 

 dentified beaked whales (including members of the 

 genera Mesoplodon and Ziphius); unidentified large 

 whales (including members of the species group 

 "large whale" in Table 1 as well as the genera Esch- 

 richtius and Eubalaena); unidentified baleen whales 

 (including members of the genera Balaenoptera, 

 Megaptera, Eschrichtius, and Eubalaena); unidenti- 

 fied small whales (including members of the species 

 groups "small whales" and "large delphinids" in Table 

 1 ); unidentified delphinoids (including members of the 

 species groups "small delphinids," 'large delphinids," 

 and "cryptic species" in Table 1); and unidentified 

 cetaceans (which could include any of the species listed 

 above or in Table 1). The number of sightings identi- 

 fied to these higher taxonomic levels is relatively small, 

 and these animals were not included in the abundance 

 estimates for individual species. 



Conditionally independent observer 



In addition to the primary observation team, a fourth 

 observer was on duty 81% of the time and looked for 

 cetaceans that were missed by the primary team. 

 This conditionally independent observer was sta- 

 tioned immediately next to the other observers, 

 searched with 7x binoculars and unaided eyes, and 

 did not reveal the presence of cetaceans until after 

 they were clearly missed by the primary observation 

 team (i.e. after they had passed abeam of the vessel 

 or were bow-riding). Nine different people served as 

 independent observers during the survey, and all 

 worked irregular schedules that overlapped with both 

 primary teams. Independent observers did not work 

 more than two consecutive hours. When a sighting 

 was made by the independent observer, that person 

 maintained their normal behavior so as to avoid 

 drawing the attention of the primary observer team. 

 Initial bearing and distance were estimated by eye 

 or with the aid of reticles in the ocular of 7x binocu- 

 lars and a hand-held protractor. After a group was 

 clearly missed by the primary team, the independent 

 observer announced the presence of the animals to 

 the data recorder and gave the initial bearing and 

 distance. Typically the vessel was diverted towards 



the group, and species composition and group size 

 were estimated by the primary observation team. 



Analytical methods 



Cetacean abundance was estimated from survey 

 data with line-transect methods (Buckland et al., 



