FISHERY BULLETIN: VOL. 83, NO. 3 



RESULTS 



Food Composition 



Of the 1,041 stomachs that were examined, 436 

 were empty. The mean volume of food in all 

 stomachs examined was 36.9 mL, of which 18.9 mL 

 was bait and 18.0 mL was prey. A complete list of 

 the stomach contents in terms of numbers, volume, 

 and frequency is presented in Appendix Table 1. No 

 larval or juvenile skipjack were found in the stomach 

 contents. Overall contributions of each category are 

 presented in Figure 3. 



In terms of the M\''RM, the gonostomatid Mauro- 

 licwi muelleri was the major prey item (MVRM = 

 26.7%). The euphausiid Ewphausia similis, with the 

 highest IRI, was also important {IRI = 1 ,998). These 

 items were major constituents of the diet throughout 

 the year. Other important fishes in terms of both the 



ALL MONTHS 



ME«N % 

 VOLUME (ranki 



17 4 7 3 5 2 25 1 14 8 4 



PERCENT FREQUENCY OF OCCURRENCE 



FiGiiRE .3. -Index of relative importance (IRI) plots for selected 

 food items of skipjack tuna caught during 1982. The food categories 

 are ranked in terms of IRI and MVRM. 



JANUARY-MARCH 



5 60 



X 



o *o 



^ Tl ^ e I 



SPECIES 



Euphausia similts 

 Maurolicus muelleri 



Auxis thazard 

 Scomber japonicus 

 FISH 



CRUSTACEANS 

 CEPHALOPODS 



IRI 



(rank) 



1756 49 (I) 

 228 60 (3) 

 3805^^) 

 47 31 <5) 

 116 29^2) 

 58 92 (4) 

 1.57 (6) 



MEAN % 

 VOLUME (rank) 



19 80 (3) 

 14 IS (4) 

 Included in fish 

 1008 (5) 

 29 55 (1) 

 23 47 (2) 

 3.02 (6) 



APRIL-JUNE 



• Auxis thazard 

 included in fish for ranking 

 ~ combined IRI = 309.66 



70 73 24.3 22 6 27 



PERCENT FREQUENCY OF OCCURRENCE 



S 60 



O 40 



13.3 59 90 90 24 



PERCENT FREQUENCY OF OCCURRENCE 



JULY-SEPTEMBER 



SPECIES 



Euphausia similis 



IRI 



(rank) 



MEAN % 

 VOLUME (rank) 



1037 32 (2) 9 60 (3) 



3710 17 (1) 55 40 (1) 



34 45 (4) 5 70 (5) 



7 60*(3) Included in liah 



7 1.76*(3) 22.87 (2) 



7.31 (5) 6.42 (4) 



036 (6) 0.01 (6) 



• Benthodesmus sp. 



included in fish for ranking 



combined IRI = 127.4 



OCTOBER-DECEMBER 



MEAN % 

 VOLUME (rank) 



34 I 3.7 3 7 18 4 9 2 0.4 



PERCENT FREQUENCY OF OCCURRENCE 



17 2 23 2 19 3 33 5 17 2 9 2 



PERCENT FREQUENCY OF OCCURRENCE 



Figure 4. -Index of relative importance (IRI) plots for selected food items of skipjack tuna. The complete data are divided into four 3mo 

 quarters (I-IV). The food categories are ranked in terms of IRI and mean percent volume. 



382 



