FOOD OF ALBACORE IN THE PACIFIC 



473 



well scattered throughout the range of Secchi disc 

 readings, but the higher values for stomach con- 

 tents are found in the mid-range of light pene- 

 tration valvies, with the highest value recorded at 

 a Secchi disc reading of approximately 22 meters. 

 An inference that can be made from figure 16 

 is that while foraging does take place in waters 

 which vary considerably in clarity, the most suc- 

 cessful foraging may take place in waters which 

 represent a compromise between (1) heavy stand- 

 ing crops of tuna forage in waters of low clarity 

 and (2) conditions of excellent visibility but where 

 the amount of tuna food is less. 



COMPETITION FOR FOOD AMONG ALBACORE, 

 YELLOWFIN, AND BIGEYE TUNA 



An investigation was made to determine 

 whether albacore compete for food with yellowfin 

 and bigeye tuna in the equatorial Pacific, since the 

 three species are caught in this general area. King 

 and Ikehara (1956) made an extensive compara- 

 tive study of the food of yellowfin and bigeye from 

 the equatorial Pacific and reported : "Despite the 

 differences we have point«d out, the foods of 

 yellowfin and bigeye are remarkably similar. We 

 conclude, therefore, that when occupying the same 

 general area the two species have the same feeding 

 liabits." 



The taxonomic categories they found in the food 

 of j^ellowfin and bigeye are compared in table 7 

 with tliose found in albacore stomach contents. 

 Table 7 shows that fewer taxa in every category 

 except one were found in albacore stomachs than 

 either yellowfin or bigeye stomachs. However, 

 more than twice as many yellowfin stomachs and 

 23 percent more bigeye stomachs were examined 

 than albacore stomachs, which lessens the weight 

 of evidence indicating more omnivorous feeding 

 by the yellowfin and bigeye. Also, most of the 

 yellowfin and bigeye studied by King and Ikehara 

 were considerably larger than the albacore with 

 which they are compared. One might expect a 

 larger yellowfin or bigeye, requiring a greater 

 daily ration than an albacore, to eat a greater 

 variety of organisms while foraging. The over- 

 all similarities in the diets of yellowfin and bigeye 

 are compared with albacore in table 7. Except 

 in two ca.ses, over half the taxa found in albacore 

 stomachs were reported in the food of yellowfin 

 and bigeye. 



TAni.K 7.—Sitiiibeni of crrtain taxonomic categories repre- 

 xcnlrrl in Hie fond of alharorc. j/clloirfln, and bigeye tuna 

 lakin on litiigliiir iiKire than ii.'> iiiilcx from land in the 

 ciiiiatorial I'uoific 



[Figures in parentheses are numbers of such categories common to yellowfln 

 or bigeye and albacore. Data on yellowfin and bigeye food from King 

 and Ikehara (1956)] 



Table 7 does not provide, however, a compari- 

 son based on a restricted geographical area. Such 

 data, available for cruise 11 of the John R. Man- 

 ning, are given in tables 8 and 9, which compare 

 the stomach contents of albacore with yellowfin 

 and bigeye caught at the same location. In these 

 instances, the food of albacore more closely re- 

 sembled that of yellowfin than of bigeye, although 

 the albacore is thought to inhabit, with the bigeye, 

 deeper waters than the yellowfin in the equatorial 

 Pacific. Nevertheless, the similarities in diet be- 

 tween both the albacore and the yellowfin and 

 albacore and the bigeye in the same specific loca- 

 tion, as well as in the same general area, are evi- 

 dence that there may be some competition between 

 the albacore and the other two species of tuna. 



SUMMARY 



1. This report is based upon the analysis of the 

 stomach contents of 544 albacore tuna captured by 

 longline, gill net, and troll fishing during 24 

 cruises by vessels of the Bureau of Commercial 

 Fisheries Biological Laboratory, Honolulu, from 

 1950 to 1957. 



2. Albacore from which stomachs were examined 

 were captured in the equatorial and temperate 

 zones of the central and northeastern Pacific. The 

 limits of the sampling area were approximately 

 latitude 16° S. to 49° N. and longitude 121° W. to 

 172° E. 



3. Troll- and gill net-caught albacore from 

 which stomachs were examined were 51-85 cm. in 

 fork length, while longline-caught albacore whose 

 stomachs were examined were between .~>4 and 117 

 cm., with 91 percent larger than 85 cm. 



4. Stomachs of the larger albacore contained 

 more food than did smaller albacore, but the 

 larger fish ate less per pound of body weight. 



