FOOD OF ALBACORE IN THE PACIFIC 



467 



habitat with decrease in Latitude has been demon- 

 strated for the great blue sliark {Prionace glauca) 

 in the central Pacific by Strasburg (1958). 



Table 'A. — Percent occurrence of fishes prominent in the 

 diet of hjngHne-cauijht albacore, according to area of 

 capture 



6 15 



to 10- 



CRUSTACEA 



(62) 



(13) 



(50) 



(18) 



I6°S-5"'S, 5°S,-I°30-S, l°30'S-l°30'M 



LATITUIDE 



Figure 9. — Variation (ee./.stomach) of major food items 

 in the rliet of equatorial longline-caught albacore, 120° 

 W.-1S0°. (Numbers in parentheses indicate .sample 

 sizes.) 



Latitudinal variations in the temperate North 

 Pacific for zooplankton, forage organisms obtained 

 by niidwater trawling, and volumes of the stomach 

 contents of longliiie- and troll-caught albacore are 

 shown in figure 10. 



30°N.-34°N. 35°N.-39''N. 40°N,.44°N, 45°N-49°r4 



tJORTH LATfTUDE 



Figure 10. — Latitudinal variations in the temperate North 

 Pacific (140° W.-180°) of zooplankton, forage orga- 

 nisms, and in the volume of stomach contents per pound 

 of body weight of 71 albacore caught by longline and 

 trolling. ( Numbers in parentheses refer to sample sizes. 

 Data obtained during summer and fall cruises, except 

 for stomach volumes from 30°-34° N., which were ob- 

 tained in winter. Zooplankton data from McGary, 

 Jones, and Austin, 19."i(>. Forage organism data from 

 King and Iversen, 1962.) 



It appears from figure 10 that zooplankton vol- 

 umes are highest to the north, trawling volumes 

 are highest south of the zooplankton peak, and the 

 albacore stomacli volumes are highest south of the 

 I)€iak trawling volumes — indications of what may 

 be the development of successive trophic levels. 



McGary, Jones, and Graham (1958) have shown 

 the existence of a "Transition Zone'' in the central 

 Xorth Pacific between the Cent ral Water Mass and 

 the Subarctic Water Mass. This Transition Zone, 

 which has temperature-salinitj' qualities inter- 

 mediate between those of the Central and Sub- 

 arctic AVater Ma.'^ses. is characterized by a north- 

 ward movement of the isotherms starting in the 

 .spring as the .surface layer is wanned and a marked 

 thermocline develops. In the sunmier the north- 

 ern limit of the warmed surface layer is at about 



654104 O — 62- 



