FOOD OF ALBACORE IN THE PACIFIC 



475 



Table !). — Conipari.snii af stoiniich contents of vf/untorial 

 albacore {A) and hif/Cj/e (HE) tuna tal;cn on longlinc 

 more than i'> milix from land diirinij cruise II of the 

 John li. Mnnning 



|(+) donotos organism present, {— ) denotes absent. Bigeye data from 

 files of the Bureau of Commercial Fisheries Biological Laboratory, 



Honolulu] 



Orpiinism 



CRUSTACEA 



Isopoda.- 



Amphipoda 



Euphausiacea 



Decapoda: 



Penaeidae 



Homaridae: Enoplometopus sp. 



MOLLUSCA 



Octopoda.. 



Decapoda: 



Enoploteuthidae: Enoploleuthis sp- 



Omraastrephidae 



Decapoda '. _-. 



VERTEBRATA (Pisces) 



Steraoptychidae .. 



Paralepididae 



Alepisauridae 



Nemichthyidae 



Myclophidae 



Holocentridae 



Braniidae.. 



Chiasmodontidae, 



Oempylidae.. 



Tetraodontidae — 

 Molidae 



Number of stomachs examined. 



Sta. 16 



A BE 



Sta. 18 



Sta. 20 



A BE 



All 

 stations 



A BE 



' Unidentified. 



8. In the equatorial Pacific, tlie larger stomacli 

 volumes were from albacore captured from lati- 

 tude 5° S. to 11^° S., whereas the highest catch 

 rates per 100 hooks for albacore occurred south of 

 5° S. It was concluded that the latitudinal abun- 

 dance of albacore in the equatorial Pacific, as deter- 

 mined from catch statistics, is not related to the 

 amount of forage consumed by albacore. There 

 was only slight latitudinal variation in the percent 

 occurrence of squid, fish, and crustaceans in the 

 stomachs of equatorial albacore. Tlie amount of 

 squid per stomach was more than twice as miicli 

 between 5° S. and 5° N. as it was south of 5° S. 

 Tlie lowest amounts of fish and crustaceans per 

 stomach were recorded from li/4° S. to li/^° N. 



9. Fishes of the families Gempylidae and 

 Bramidae did not occur in the stomaclis of all)a- 

 core captured by longline in the temperate North 

 Pacific, whereas they were found in 28.5 and 21.5 

 percent respectively of the stomachs of loiigline- 

 caught albacore from equatorial waters. It is 

 suggested this may reflect the vertical distribu- 

 tion of these food fishes in these two areas. 



10. In the temperate North Pacific, the highest 

 stomach volumes of albacore troll-caught in sum- 

 mer between 140° W.-180°, were found to the 

 south of successive peak volumes of organisms 

 captured by midwater trawling and zooplankton 

 tows. This may show successive tropliic levels as- 

 sociated with an advancing oceanographic and 

 biological "frontier" during summer in the Transi- 

 tion Zone of the temperate North Pacific. 



11. With respect to longitudinal variations in 

 albacore food in the equatorial Pacific, the highest 

 stomach volumes were recorded in the western 

 portion of the sampling area while the high zoo- 

 plankton values were recorded in the east central 

 equatorial Pacific. In the temperate North Pa- 

 cific albacore stomach volumes were higher from 

 120° W.-140° W. than they were from 1-40° 

 W.-180°. 



12. In the temperate North Pacific, there was 

 little seasonal diti'erence in the volume of albacore 

 food. In the equatorial Pacific the amount of 

 squid and fish varied slightly and irregularly from 

 January through September. From October 

 through December, based on a small sample, the 

 amount of fish consumed was about twice the 

 amount consumed by albacore during other 

 months. In all months more fish than squid was 

 eaten by the equatorial albacore. 



13. The amount of squid eaten by equatorial 

 albacore increased with an increase in distance of 

 the place of capture from nearest land. The 

 amount of fish eaten was highest near land (0-2-t 

 miles) and then varied irregularly in an offshore 

 direction. Reef-associated organisms appeared 

 most frequently in the diet of albacore captured 

 near land. 



1-4. Feeding by troll-caught albacore in the tem- 

 perate North Pacific occurred throughout the day. 

 AVhile the lower stomach volumes were found in 

 albacore captured dui-ing 1100-1600 houi-s, the evi- 

 dence for distinct periods of feeding was not clear. 

 Squid were found in more than 10 percent of alba- 

 core stomachs from 0900 to 1700 hours and sauries 

 were common in albacore stomachs (more than 10 

 percent) throiiglioiit tlie day (0600-2000). Evi- 

 dence is presented liiat alliacore also feed during 

 the night. 



15. The higher stomach A-olumes of albacore 

 troll caught in the temperate North Pacific oc- 

 curred in waters of midclarity, as measured by 

 Secchi disc observations. 



