In the present study, we examined the stomach con- 

 tents of four species of Thunnus in the western North 

 Atlantic: T. albacares (Bonnaterre), the yellowfin; T. 

 alalunga (Bonnaterre), the albacore; T. t. thynnus (Lin- 

 naeus), the Atlantic bluefin; and T. obesus (Lowe), the 

 bigeye. The specimens examined were obtained during a 

 series of exploratory longline cruises over the period 1957- 

 64 by the Bureau of Commercial Fisheries (now National 

 Marine Fisheries Service) MV Delaware, before a major 

 fishery was established in the region. While fishing for 

 tunas, lancetfishes of the genus Alepisaurus were often 

 hooked by the longline. In this capacity at least, the 

 lancetfishes were competing with tunas; being thus an 

 apparent competitor, it seemed worthwhile to examine 

 also the stomach contents of Alepisaurus taken with 

 Thunnus. Alepisaurus forage has previously been in- 

 vestigated in the Atlantic by Haedrich (1964). Parin et 

 al. (1967) reported on the feeding habits of Alepisaurus in 

 the Indian Ocean. In the Pacific, lancet fish feeding 

 habits have been reported on by Haedrich and Nielsen 

 (1966), Kubota and Uyeno (1969), Rancurel (1970), and 

 Kubota (1973). 



Included in the present study are both species of 

 lancetfishes, Alepisaurus ferox Lowe and A. brevirostris 

 Gibbs. No distinction is made between species, however, 

 because much of the data were collected before the latter 

 was described by Gibbs (1960). 



and, on one cruise, east to the Azores (Figure 1). 

 Specimens were taken from depths of 10-60 m. Longline 

 gear and methods used were described by Squire (1962) 

 and Wilson and Bartlett (1967). 



Most of the Thunnus stomach contents were collected 

 by Robert H. Gibbs, Jr. and Bruce B. Collette in con- 

 junction with a study of the anatomy and systematics of 

 the genus Thunnus (Gibbs and Collette 1967). Methods 

 to obtain stomach contents were used that would not 

 damage the tuna specimens. The stomach contents of 

 Thunnus were obtained through a longitudinal ventral 

 incision through which the stomach was pulled, the con- 

 tents were removed, and the emptied stomach pushed 

 back into place. As a result, the total contents were not 

 always obtained. The stomach contents that were 

 collected for each specimen were preserved in 10% For- 

 malin. Size (mm fork length (FL) ) and weight of the 

 tuna were usually recorded. 



Alepisaurus stomach contents were obtained by shak- 

 ing the specimen head-down over a bucket, after the 

 removal from the longline hook. The lancetfish's wide 

 mouth, esophagus, and stomach allowed its stomach 

 contents to fall out readily into the collection bucket. 

 Contents were then preserved in 10% Formalin. 



Some stomach contents were identified at sea, record- 

 ed, and discarded; others were identified at the Woods 

 Hole Oceanographic Institution and Boston University. 



MATERIALS AND METHODS 



We examined the contents of 395 Thunnus stomachs 

 (281 T. albacares, 52 T. t. thynnus, 48 T. alalunga, and 

 14 T. obesus) and those of 89 Alepisaurus. Number, size 

 range, and mean size of the Thunnus and Alepisaurus 

 specimens are presented in Table 1. All specimens were 

 collected by longline from the western North Atlantic off 

 the eastern coast of the United States north of Bermuda 



Table 1.— Numbers, size ranges, and mean sizes of Thunnus spp. and 

 Alepisaurus examined. 



N 



Size range 

 (cm FL) 



Thunnus albacares 



281 



74-166 



114 



Thunnus alalunga 



48 



96-106 



101 



Thunnus thynnus 



52 



158-232 



188 



Thunnus obesus 



14 



142-165 



149 



Alepisaurus sp. 



89 



48-138 



— 



Figure 1. — Area sampled (crosshatched) for Thunnus and Alepisaurus by longline in the western North Atlantic. 



2 



