FISHERY BULLETIN; VOL. 71, NO. 4 

 Table 6. — Stomach contents of yellowfin tuna and spotted porpoise taken in a single net haul; Haul 5. 



' Fish counted in 19 stomachs. 



2 Whole squid counted in 16 stomachs not saved ; only samples of beaks were saved for identification. 



was present in the tuna (beaks from three indi- 

 viduals), the only occurrence in tuna in the six 

 hauls. 0)iykia, however, was again present in 

 the porpoise but not in the tuna. 



Some of the frigate mackerel were sufficiently 

 undigested to allow them to be measured. 

 Thirty five ranged from 18 to 29 cm fork length 

 (average 24 cm), and sizes did not differ in por- 

 poise and tuna. 



Haul 6 



Nineteen stomachs of spinner porpoise were 

 examined in this haul, and all were empty. The 

 spotted porpoise contained freshly ingested 

 Auxis and squid (Table 7), in about the same 

 ratio as in Haul 5, but the tuna contained only 

 small amounts of Euphylax dovii, along with 

 well-digested fish and squid remains. The three 



species in this haul had fed on different food 

 and/or at different times. 



Summary of Results 



Ommastrephid squid A (probably Dosidicus 

 gigas) was the most important prey species in 

 terms of co-occurrence in the tuna and both 

 species of porpoise as an important food item 

 (Table 8). The greatest overlap between species 

 was in Haul 5, when Auxis and the ommastre- 

 phid were important in the tuna and the spotted 

 porpoise. As regards specialization, Diogenich- 

 thys sp., Benthosema panamense, Vinciguerria 

 sp., and Bregmaceros sp. were important only 

 in the spinner porpoise, and Euphylax dovii was 

 important only in the tuna. When spinner por- 

 poise were sampled (three hauls), the rate of 

 occurrence of empty stomachs and the state of 



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