FOOD OF BIGEYE AND YELLOWFIN TUNA 



63 



Table 1. — Distribution of yellowfin and bigeye stomachs collected from the central Pacific, identified by vessel, cruise, 



time of year, and locality 



I Of this number, only 38 (29 percent of the catch) were considered comparable in respect to time and place to the bigeye collections and were included in 

 this report. 



' Of this number, only 87 {19 percent of the catch) were included in this report for the same reason as above. 



1 — i — I — I — r 



YELLOWFIN 



1 — I — \ — I — I — I — I — I — 1 — \ — r 



I r^^rT^^rrr . 



FORK LENGTH (CM ) 



BODY WEIGHT (LBS ) 



-1 — 1 — t — I — ' — I — I — I — I — I — r- 



BIGEYE 



200 

 360 



FiGiRE 2. — LeiiKth-frequeiicy distribution of yoUowfin 

 and bigeye tuna from which stomach.s were collected. 



derived from length measurements converted by 

 means of length-weight tables provided in the 

 POFI Scientific Field Manual (unpublished). 



METHODS 



At sea, the stomacii was removed as soon as 

 possible after the fish was captured, placed with 

 any iTgui-gitaled material in an unbh'aclied-inuslin 

 bag. and preserved in lO-peicent formalin. A 



label bearing date, species najme, fork length, fish- 

 ing method, hook number, bait used, name of 

 observer, vessel, and cruise number was placed 

 with each stomach. Tuna landed with their 

 stomachs everted were not sampled. 



The stomach was removed by one of the follow- 

 ing methods: (1) The abdominal cavity was 

 opened by a longitudinal midventral incision, the 

 small intestine was severed posterior to the pyloric 

 valve, and the stomach was freed by cutting 

 through the esophagus; or (2) the gill membrane 

 was slit along the line of attachment with the 

 cleithrum posterior to the fourth gill arch, the 

 viscera was pulled out, and the stomach was 

 removed by cutting througli the small intestine 

 and esopliagus. 



In the laboratory, the stomachs were soaked 

 in fresh water for a period of 16 to 24 hours to 

 remove excess formalin. Each stomach was then 

 slit open, and the contents were carefully removed 

 and separated into groups according to kind of 

 organism. Identifications were made as com- 

 pletely as was practicable, and the number of 

 each species or group of organisms present was 

 recorded. Each species or group was measured 

 volumetrically by the displacement of water in 

 a graduated cylinder of appropriate size. Bait 

 used to capture tlie tuna was omitted from this 

 analysis. The methods and literature used in 

 the identification of the food organisms were 

 essentially the same as that employed bv Reintjes 

 and King (195.S) and will not be I'eviewed here. 

 Berg's (1947) system of classification and nomen- 

 clature was primarily useii foi' the family names 

 of tlie forage fishes. 



