Blue Whale 



Balaemptera musculus (Linnaeus, 1758) 



Movement patterns of baleen whales generally consist of poleward 

 shifts in spring/summer and shifts back towards the equator in 

 autumn/winter. Unfortunately, however, neither the seasonal distribu- 

 tion nor the routes travelled by blue whales m the eastern North Pacific 

 are well mapped. Whaling records indicate that some degree of north- 

 south movement takes place, but in parts ot the species' range blue 

 whales are present in unexpected months. There may be geographically 

 separate stocks whose wanderings, viewed collectively, defy' recognition 

 of neat migratory patterns for the species in the eastern North Pacific. 



Blue whales are distributed from the waters off Panama north to 

 the Aleutian Islands, venturing occassionallv into the Bering Sea and 

 rarely, perhaps, even into the southern Chukchi Sea. An apparently 

 isolated, year-round stock exists between about 800 and 2000 nm off 

 Central America between latitude 7 N and latitude 9 N and some of 

 the blue whales seen in the Sea of Cortes, as far north as the northern 

 Midriff Islands, mav remain there all year. The blue whales encoun- 

 tered in the SCB and CINMS, however, are probably part of a more 

 general eastern North Pacific stock best known from Mexico to the 

 northern Gulf of Alaska and north central North Pacific. 



Blue whales feed almost exclusively on kriU and pelagic red crabs, so 

 their protracted stays in a given area are related largely to availability of 

 ample supplies of these organisms. Blue whales usually occur singly or 

 in pairs in most of their range, but large groups ('40 or more) have been 

 seen in areas where prey are abundant, particularly off Mexico. 



f IGURt 9. Sightings oi blue whales are fairlv reguUr Irom June through 

 September-October along the edge of the Patton Escarpment, outside the 

 Channel Islands. During this period some whales venture over the shelf, 

 especially near the outermost islands. (Photos from 4 nm, top, and 7 nm, 

 bottom, north of San Miguel Island, August 1979 bv D. Seagars.) 



Blue whales can be seen off the west coast of Baja California fi-om 

 about February through July. Peak numbers have been reported there 

 in April. Whales appear in the area again in October but have not been 

 reported between November and January. The absence of sightings in 

 autumn/wmter may reflect reduced searching effort during those 

 months, but Norivegian whalers working the Baja coast in the 1920s 

 and 19^05 killed blue whales primarily in late winter through spring 

 between Cabo San Lucas and Cedros Island. 



Blue whales are seen fairly frequently off Southern California from 

 June through December. Encounters have been most frequent in July 

 through October. Many animals appear to be migrating northward |ust 

 outside the Channel Islands, along the edge of the Patton Escarpment, 

 or to be lingering around Tanner or Cortes banks, along the Cortes 

 Ridge, or north of Santa Rosa and San Miguel islands. We are aware of 

 occasional sightings within the SCB in the last 20 years, from: the 

 Coronodo Islands, San Diego Bay, Pacific Beach, La Jolla, San Clem- 

 ente Island (east and north shores;, Santa Catalina Island, Santa 

 Barbara Island, San Nicolas Island, San Miguel Island, to withm 

 approximately 200 m of Castle Rock in October, and in the northern 

 Santa Barbara Channel to within 5 nm of the mainland coast in 

 September and November. Blue whales, thought to be the same 

 individuals, have been reported around San Miguel Island for a month 

 or more at a time during summer and autumn. This may mean that in a 

 given year some whales do not \enture north of Point Conception even 

 as the population center shifts northward. 



Figure 10. A blue whale takes a breath off San Nicolas Island m 1975. 

 Occurrence of this species near the CINMS can reasonably be expected to 

 increase as the populations grow. (Photo by J. D. Hall.) 



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