whales between lat. 7° and 10°N. Although indi- 

 vidual species of baleen whales were not enumer- 

 ated by Volkov and Moroz, two sightings of blue 

 whales were made on 29 March 1975 and are pre- 

 sented here (Table 1, Vni/shitelnyi cruise). 



Typically blue whales are seen along the Baja 

 California coast in October while migrating 

 southward, and subsequently reappear off Baja 

 California in large numbers in March-June on 

 their northward migration (Rice 1974). The 

 whereabouts of the North Pacific blue whales dur- 

 ing the winter months is completely unknown, but 

 this is probably due to the lack of sighting effort. 

 For instance, Japanese whale scouting has been 

 carried out systematically since 1965, but their 

 effort has been restricted to the Pacific waters 

 north of lat. 20°N (Wada 1977). 



Two theories have evolved regarding the win- 

 tering grounds of the blue whale. Wheeler ( 1946), 

 suggested that blue whales winter within a lim- 

 ited area of the subtropics. He maintained that 

 whales congregate in large groups in areas not 

 frequented by vessels. A second theory maintains 

 that wintering blue whales disperse between the 

 feeding grounds and the tropics (Harmer 1931; 

 Mackintosh 1942). Presented in this note is a 3-yr 

 record of blue whales sighted in the northeastern 

 tropical Pacific. Reference is made to migration, 

 whale groupings, behavior, and to the oceano- 

 graphic features of the sighting area. These recent 

 sightings were made by trained observers aboard 

 vessels involved with the National Marine 

 Fisheries Service Tuna/Porpoise Research Pro- 



gram. Sighting information from other experi- 

 enced observers has also been contributed. 



Shipboard identification of rorquals is difficult 

 and this problem was compounded by the fact that 

 most of the sightings mentioned in this paper were 

 incidental to ship's activities. However, the blue 

 whale is easily discerned from other rorquals by 

 the recognition of the following combination of 

 characteristics: 



1. Mottled blue-grey coloration. All other ror- 

 quals are uniformly steel grey on the dorsal 

 surface. 



2. A small dorsal fin of varying shapes located in 

 the posterior third of the body. The dorsal fin of 

 the sei, fin, and brydes whales is larger, falcate 

 shape, and placed farther anterior than the 

 blue whale dorsal fin. 



3. A U-shaped rostrum. The rostrum shape of 

 other balenopterids is more pointed. 



4. Tall, dense, disperse blows. Generally, the blow 

 of the sei and brydes whales is low and dissi- 

 pated, while the fin whale has a tall conical- 

 shaped blow. 



A total of 1 1 cruises are discussed in this report, 

 covering the period from January to May for 1971, 

 1 975, 1 976, and 1 977. 1 The area of effort and sight- 

 ings of blue whales are reported in Figure 1. The 



'No blue whale sightings were made in 1977. although two 

 cruises have been included in Figure 1 to complement survey 

 effort. 



Table l. — Annotated listofblue whale sightings by National Marine Fisheries Service observers in the northeastern tropical Pacific, 



January-May 1971-76. 



916 



