Baker et al,: Population characteristics of Megaptera novaeangliae in southeastern Alaska 



431 



and with field efforts during the summers of 1981-82 

 (Baker et al. 1985). 



Prey assessment 



Humpback whale prey species were assessed in Glacier 

 Bay with a Ross Fineline 250C recording fathometer 

 equipped with a 22° beam, 105-kHz transducer. In 

 Frederick Sound, prey were assessed with a Lowrance 

 recording fathometer equipped with a 250-kHz trans- 

 ducer. Putative identification of primary prey species 

 type (e.g., euphausiids vs. schooling fish) was based on 

 qualitative differences in target strength, as judged 

 from the relative intensity of fathometer recordings, 

 and the size, shape, and depth of prey schools. These 

 interpretations were based on reference to previous 

 documentation of humpback whale prey using quan- 

 titative hydroacoustics and net sampling (Wing and 

 Krieger 1983, Krieger and Wing 1984 and 1986). On 

 occasion, observations of feces from feeding whales or 

 the presence of prey species at the surface provided 

 direct confirmation of primary prey species type. 



Individual identification 



We attempted to individually identify all humpback 

 whales encountered by collecting photographs of the 

 ventral surface of the whales' flukes. The uniqueness 

 of the coloration, shape, and scarring pattern of the 

 flukes' ventral side allowed for the reliable identifica- 

 tion of individual whales (Katona et al. 1979). Because 

 our primary objective was to collect individual iden- 

 tification photographs for use in capture-recapture 

 analyses and the estimation of long-term reproductive 

 rates, we did not attempt to count unidentified whales 

 along the survey tracks. Consequently, all references 

 to 'sightings' or 'observations' of whales are based only 

 on photographs of unique individuals. 



Methods for processing and comparison of fluke 

 photographs followed that described by Perry et al. 

 (1988). Photographs of whales were taken with a 35 mm 

 single-lens reflex camera equipped with a motor drive 

 and a 300mm telephoto or 70-210mm zoom lens. High- 

 speed (ASA 400-1600) black-and-white film was used. 

 From each observation of a whale or group of whales, 

 the best photograph of each individual's flukes was 

 printed and assigned a "fluke observation" or iden- 

 tification number. Information on the location, date, 

 and social affiliation of each fluke identification was 

 stored in a data retrieval file at the University of 

 Hawaii Computing Center. During the matching of 

 fluke photographs, a whale that was identified on more 

 than one occasion was also assigned an "animal" 

 number. This number allowed us to reference all fluke 

 observations, or identifications, of that individual. All 



fluke photographs were judged to be of either good, 

 fair, or poor quality. Good- and fair-quality photographs 

 showed at least 50% of both flukes at an angle suffi- 

 ciently vertical to distinguish the shape of the flukes' 

 trailing edges. For this study, poor-quality photographs 

 were deleted from the data set. 



Results 



Abundance and regional fidelity 



A total of 257 humpback whales, including 19 calves, 

 were individually identified in southeastern Alaska dur- 

 ing 1986. This total includes 29 adults identified only 

 in Glacier Bay, 183 identified only in Frederick Sound, 

 16 identified only in Sitka Sound or Chatham Strait, 

 and 10 adults common to more than one subregion. The 

 majority (n 130, 54.6%) of the 238 adults identified in 

 1986 had been identified in southeastern Alaska pre- 

 viously, based on comparison with photographs col- 

 lected by University of Hawaii researchers and asso- 

 ciates during the years 1979-85 (Perry et al. 1988). The 

 addition of the 108 newly identified individuals to the 

 existing catalogue of photographs resulted in a cum- 

 ulative total of 579 adult whales identified in south- 

 eastern Alaska across the 8 study years (Table 1). 



To determine the fidelity of humpback whales to 

 regional feeding grounds, photographs collected from 

 southeastern Alaska during 1986 were compared with 



