68 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 2. — Variation in volume and composition of stomach contents of yeltowjin and bigeye tuna, by size groups 



is illustrated in figure 8. For the yellowfin, there 

 is an increase in average volume of stomach con- 

 tents with increasing depth of capture; for the 

 bigeye, the largest average volume was found at 

 the intermediate depth, with the deep-caught fish 

 ranking second. For both species, the most con- 

 sistent feature was the low average food volume 

 for the shallow-cauglit fish. 



In the yellowfin, the increase with depth is 

 largely due to a higher consumption of fish, 

 particularly juvenile tunas (Thunnidae) and sun- 

 fishes (Molidae), at the intermediate and deep 

 levels; the squid are utilized about equally at all 

 three depths. In the bigeye taken on the deeper 

 hooks, tliere is also greater utilization of fish, 

 particularly pomfrets (Bramidae) and snake 

 mackerels (Gempylidae), with squid decreasing in 

 relative importance witii depth but varying irreg- 

 ularly in absolute vohime. Despite these rather 

 minor differences, there is no marked variation in 



composition of stomach contents over this range 

 of depth (estimated at 150 to 500 feet), which may 

 be evidence that both the forage organisms and 

 the tuna range throughout this water layer. 



Variation in Food with Distance from Land 



In tlie routine processing of the stomach data, 

 the records were classified according to the distance 

 of the place of capture from the nearest emergent 

 land. An arbitrary scale (0-24 miles, 25-99 miles, 

 100-399 miles, and 400 miles and more) was used 

 as in the previous study (Reintjes and King 1953). 

 \o l>igeye stomachs were collected at 0-24 miles, 

 and few (eigiit) were collected in the 25-99 mile 

 interval; tlierefore, the data do not provide the 

 desired information on difterences in the food 

 related to this feature. There was some indica- 

 tion that the consumption of squid and pomferts 

 by the bigeye increased in an offshore direction, 

 as compared with tlieir uniform utilization by the 



