298 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



achs were examined, ranged in size from 85 to 155 

 cm. (26 to 160 lb.) and averaged about 120 cm. 

 (74 lb.) . The fishing method, localities, and catch 

 data for this cruise have been described by Iver- 

 sen and Yoshida (1956). 



Table 18 lists, for 16 days of cruise 20, the cate- 

 gories of organisms that comprised 1 percent or 

 more, by volume, of the trawl catches and tuna 

 stomach contents. Except for the first three sta- 

 tions (stations 1, 2, and i) , all the trawl hauls were 

 made just after twilight or at night between 1840 

 and 2030 (zone time). It is obvious that whereas 

 the trawl consistently caught such animals as si- 

 phonophores, chaetognaths, crustaceans, and tuni- 

 cates, these organisms were largely missing from 

 the tima stomach contents. Decapod molluscs 

 (squids), on the other hand, were prominent in 

 tuna stomachs, but poorly sampled by the trawl. 

 Among the families of fishes, the Thunnidae (Kat- 

 sim)onus pelamis), Tetraodontidae, Molidae, 

 Sternoptychidae, Bramidae, Nomeidae, and Bal- 

 istidae were commonly found in the yellowfin 

 stomachs but were not captured in any quantity 

 by the trawl. Most of these families may be con- 

 sidered as pelagic fishes characteristic of the sur- 

 face layer both in periods of light and darkness. 

 For the Sternoptychidae, Marshall (1960) cites 

 records of Sternoptyx diaphana being taken at 

 600-800 m., and Argyropelecus hemigymniis at 

 150-500 m. at night but below 500 m. during the 

 day. The Myctophidae, Nemichthyidae, Gonosto- 

 midae, and Stomiatidae, which were the principal 

 fishes captured in the trawl, are bathypelagic in 

 distribution, occurring at the middepths during 

 the day (Marshall, 1960 : p. 82-88), but migrating 

 to the surface layer at night. The virtual lack of 

 these fishes in the food of yellowfin may indicate 

 that this species feeds principally in the daytime 

 and in the surface layer. 



Some fishes, such as Thunnidae, Balistidae, and 

 Gempylidae, commonly found in tuna stomachs, 

 are strong, fast swimmers, and their absence from 

 the trawl catches may simply indicate the ineffec- 

 tiveness of the gear, and not that the timas were 

 particularly selective in their feeding, or that the 

 trawl and the tunas were sampling different 

 environments. 



The results of two cruises to the central North 

 Pacific, Manning cruises 22 and 23, provide an op- 

 portunity to compare the composition of trawl 



Table 18. — Percentage composition of the stomach con- 

 tents of longline-caught yelloicfin tuna and of the 

 catches of the €-foot Isaacs-Eidd trawl on John R. 

 Manning cruise 20, equatorial Pacific, 1954 



Organisms i 



May 17: 



Lonpline and trawl, station 1; 7 stomachs: 



Siphonophora 



Chaetugnatha 



Amphlpoda- 



Fhabdosoma sp 



Octopoda 



Sepioteuthis sp... __ 



Unidentified Decapoda (MoUusca) 



Tuiiicata 



Katsuwonus pelamis. 



Nomeidae 



Acanthuridae _ _ _ 



Ostraciidae , 



Lactoria diaphanus 



Bramidae- 



Ranzania laevis 



Apogonldae- 



Leptocephali-- 



Larval fish _. 



Unidentified fish 



May 18: 



Longllne and trawl, station 2; 3 stomachs: 



Siphonophora. _ 



Medusae 



Chaetognatha,- 



Amphipoda __ _,. 



Argonautldae 



Unidentified Decapoda (MoUusca) 



Salpidae 



Katsuwonus pelamis 



Acantluiridae-,- 



CoUybus drocfime 



Tetraodontidae 



Leptocephali _ 



Larval fish- - 



Unidentified fish _ 



May 19: 



Longllne and trawl, station 4; 1 stomach: 



Siphonophora _ 



Chaetognatha 



Amphipoda.- -- 



Pbronima sp _ 



Rhabdosoma sp .- 



Unidentified Decapoda (MoUusca) 



Salpidae -_. 



Lactoria diaphanus 



Bramidae 



Larval fish _._ 



Unidentified fish -. 



May 22: 



Longline, station 8; trawl, station 9; 1 stomach: 



Siphonophora 



Medusae.- - - - 



Euphauslacea - --- 



Octopodldae 



Argonautldae - 



Pyrosomatldae.-- --- - 



Salpidae - - - 



Lampanyctus sp 



Photostomias sp 



Eustomtas sp. --- -- 



Thysanactis sp --- 



Unidentified fish - - 



May 23: 



Longline, station 10; trawl, station U; 7 stomachs: 



Siphonophora --- --- 



Euphauslacea - 



Sagesles sp -- 



HoplophoTus typus 



Octopodldae --- 



Oni/coteuthis banksii - 



Unidentified Decapoda (MoUusca) - 



Unidentified Tunicata - 



Pyrosomatldae - --- 



Salpidae --- 



Isistius brasitiensis - 



Lactoria diaphanus -- 



Unidentified Bramidae - 



CoUybus drachme 



Anoploffasler cornutus - 



Chautiodus sp -- 



Nemichthys scolopaceus - 



Diaphus sp--- 



Stomach 

 contents 



1 Includes all organisms or groups o( organisms comprising 1 percent or 

 more, by volume, ol the stomach contents or of the trawl catches. 



