570 



Fishery Bulletin 102(4) 



fully identified of which 191 were unique individuals 

 i Table 2). Of these 191, 83 (44%) had been seen in this 

 area in more than one year within this time period. The 

 proportion of animals seen more than one year changed 

 over the course of the study ( Fig. 4). The proportion of 

 whales identified each year that had been seen in others 

 years decreased annually (Fig. 4, regression r- = 0.63, 

 P=0.002); the most dramatic drop occurred between 

 1998 and 1999. 



Photographs of humpback whales documented animal 

 movements within the study area and provided some 

 insight into possible reasons for the high sighting rates 

 during the 2002 ship surveys. On two occasions, the 

 same humpback whale was identified on different days 

 in a slightly different area and represented a duplicate 



sighting of this animal from the ship survey. It is pos- 

 sible that shifting humpback whale distribution during 

 the course of the 2002 survey could have occurred in 

 a manner that resulted in the same animals being 

 encountered multiple times and that elevated the sight- 

 ing rate and line-transect abundance estimate (Fig. 3). 

 We cannot test this hypothesis because other animals 

 may have shifted in a manner that they avoided being 

 detected at all. 



Abundance of humpback whales from capture-re- 

 capture models yielded estimates of 89 to 343 whales 

 (Table 5, Fig. 3). These estimates tended to increase 

 over the course of the study from a low of 89 whales 

 for 1994-95 to a high of 343 for 2000-2001 and 230 

 for 2001-2002 (regression r 2 = 0.60, P=0.02). There was 

 fairly good agreement between the capture-re- 

 capture and line-transect estimates until 2002 

 (Fig. 3). 



A total of 17 of the 191 (9%) whales that we 

 identified off northern Washington had also 

 been photographed off California and Oregon 

 (Table 6). Interchange of whales seen off north- 

 ern Washington and other feeding areas to the 

 south decreased as distance among feeding ar- 

 eas increased. About 10% (10 of 105) of the 

 whales that were identified off Oregon were 

 also photographed off northern Washington. 

 This rate of matching dropped below 3% (8 of 

 313) off northern California and continued to 

 decrease to no interchange seen for whales pho- 

 tographed off southern California. 



The proportion of whales that were seen in 

 areas to the south appeared to change over 

 the course of the study. From 1989 to 1998, 

 when resighting rates between years within 

 our study area were highest, we also had a 

 higher proportion of interchange with feeding 

 areas to the south (13 of 109 whales or 12%). 

 From 1999 to 2002, after resightings within 

 our region decreased, there was also a decrease 



