FISHERY BULLETIN: VOL. 75. NO. 4 



number of factors acting in an interrelated matrix 

 which impacts the fish both directly through 

 physiological means and indirectly through forage 

 availability. We postulate that the factors include, 

 but are probably not limited to: 1 ) habitat temper- 

 ature preference, 2) biological productivity, and 3 ) 

 thermal gradients as they affect the albacore's 

 thermoregulation processes, and that these fac- 

 tors act in an interrelated way superimposed on 

 the innate drive of the fish to migrate across the 

 North Pacific Ocean. 



HABITAT TEMPERATURE PREFERENCE. 



— The distribution and relative abundance of al- 

 bacore are related to sea-surface temperature (Cle- 

 mens 1961; Johnson 1962; Panshin 1971; and 

 others). The habitat temperature preference for 

 albacore ranges from approximately 16° to 19°C 



(Clemens 1961; Laveastu and Hela 1970). This 

 temperature range is found in the upper mixed 

 layer waters of the Transition Zone in spring. 

 Near-surface waters to the south of the Transition 

 Zone are generally warmer than this and those to 

 the north cooler. 



The sequence of spring-summer warming of the 

 surface layer along a section between Honolulu 

 and San Francisco during 1972 is illustrated in 

 Figure 14. The Transition Zone boundaries iden- 

 tified by the abrupt changes in depth of isotherms 

 at intermediate depths fall between long. 130° and 

 140° W. The habitat temperature preference range 

 for albacore (16° to 19°C) is shown with shading. In 

 early and mid-spring (upper left) only the Central 

 waters have preferred temperatures and these 

 waters occur down to a considerable depth, almost 

 200 m. In subsequent time periods, a shallow sur- 



APRIL 15-19. 1972 



^HONOLULU- 

 2.000 



NAUTICAL MILES - 



1,500 1,000 



SAN FRANCISCO^ 



500 



MAY 27-31,1972 



^HONOLULU - 

 2.000 



NAUTICAL MILES- 



1.500 1.000 



SAN FRANCISCO-. 



500 



800 



1.200 



JUNE 24-28. 1972 



VOYAGE 45 



-HONOi 



2.000 1.500 



-NAUTICAL MILES 

 1.000 



SAN FRANCISCO- 



500 



I45°W I40°W 



LONGITUDE 



30°W I25°W 



JULY 22-26,1972 

 ^HONOLULU— 



NAUTICAL MILES - 



1.500 1.000 



VOYAGE 4 7 

 -SAN FRANCISCO^ 



LONGITUDE 



FIGURE 14.— Vertical temperature sections on a transect from Honolulu to San Francisco during April to July 1972. The temperature 



range between 16° and 19°C (60.8° and 66.2°F) is shaded. 



818 



