+-3^ 



- O 



-icr 



Figure 1 . — Survey effort for blue whales in the northeastern tropical Pacific over 1 1 cruises from January to June in 197 1 , 1975, 1976, 

 and 1977. Each numeral represents the total number of times that vessels entered a 1° block. Darkened blocks indicate blue whale 

 sightings. 



fact that blue whales have been sighted in the 

 same general area for three winters indicates that 

 North Pacific blue whales may have a distinct 

 wintering ground to which they migrate each 

 year. 



The location of the suggested wintering grounds 

 indicated by the sighting data are lat. 7°29'- 

 10°31'N and long. 95°25'-99°00'W.2 Only 1 of the 

 20 blue whale sightings (lat TSO'N and long. 

 83°04'W, 23 January 1975, a solitary individual) 

 was outside of these bounds. The equatorial sight- 

 ing location of this whale may indicate that either 

 it was not from the North Pacific population, or 

 that North Pacific blue whales do not restrict mi- 

 gration to the hypothetical wintering grounds. 



^Cruikshank's observations, in 1928, were also in this area. 



Whale Groupings and Behavior 



Blue whales are believed to be found singly or in 

 pairs (Leatherwood et al. 1976). In fact, Nemoto 

 ( 1964) reported that blue whales observed on the 

 summer feeding grounds were solitary. However, 

 five of the sightings reported here were aggrega- 

 tions of whales dispersed over several square 

 miles. Many of the whales were paired. The multi- 

 ple sightings on 7 February 1975 and 13 February 

 1976 appear to be mostly of solitary animals (Ta- 

 ble 1). However, on both days, no less than 40 n. mi. 

 separated the first and last whales sighted. Also, 

 four out of the five whales observed on 7 February 

 1975 were headed in a northeasterly direction. 

 This information may indicate that these appar- 

 ently solitary whales were part of a large dis- 

 persed group. 



917 



