64 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



A detailed list of the food organisms found in 

 the tuna stomachs is presented in the appendix 

 (table 11). For each kind or group of organisms 

 there are shown (1) the total number of sucli 

 organisms, (2) the number of stomachs in which 

 they occurred, (3) the percentage of occurrence, 

 (4) the total aggregate volume of each food 

 element, and (5) the percentage of total volume. 



Regardless of the method or methods of anal- 

 ysis used, there are many uncontrollable variables 

 inherent in food studies which detract from the 

 precision of the results. It is our belief, however, 

 that for a fish with a generalized diet, such as 

 that of the tuna, any of the commonly used meth- 

 ods of evaluation will give substantially the same 

 results if a sufficiently large number of specimens 

 are examined. In reporting the results of our 

 studies on tuna food we use both the percentage- 

 of-occurrence and the percentage-of-volume meas- 

 urements (as described by Reintjes and King 

 1953) and the average volume of food per stom- 



ach. The food items that rank liigh in number, 

 volume, and frequcncv of occurrence are most 

 likely to be important foods. 



No attempt has been made to apply statistical 

 tests of significance to the data. It is likely tliat 

 the variates used — volume of food per stomach, 

 percentage of occurrence, and percentage of total 

 volume of the organism — are not distributed nor- 

 mally and that the means are correlated with the 

 variances or standard deviations. To apply 

 meaningful tests of significance, transformation of 

 the data would be necessary. Moreover, several 

 of the comparisons that will be made involve 

 two-way or three-way classification of the data. 

 Even if suitable transformations were derived, 

 the application of advanced analysis of variance 

 techniques would be hampered by unequal 

 subclass numbers. 



Furthermore, it appears that in both yellowfin 

 and bigeye there is an increase in mean volume 

 of food per stomach with increase in size of fish. 



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Fir.URE 3. — Exainple.s of type.s of food commonly found in .stomach.s of yellowfin and bigeyf tunas: Left to right: pom- 

 fret (1), truncated .sunfi.sh (1), snake mackerel (1), lancet fish (1), shrimps (3), viper fish (15), hatchet fi.sh (3), euphausids 

 (8), juvenile stomatopods (3), crab megalopa (12), squid (3), and paper nautilus (1). 



