FISHERY BULLETIN: VOL. 80, NO. 2 



The remaining species— of six families— all 

 appear basically adapted for capture and inges- 

 tion of relatively large prey. All have large fangs, 

 none have well-developed gill rakers, and in most 

 the cardiac portion of the stomach is elongate 

 and, in some species, obviously capable of dis- 

 tension to accommodate prey over one-half the 

 predator's body length. All these species except 

 Malacosteus danae have eaten relatively large 

 prey (usually at least 20% of SL) at all sizes and 

 most of them exclusively such items. There was 

 rarely more than one prey item in a stomach. 



Juvenile Thysanactis dentex and Astronesthes 

 spp. — especially A. indicus — were the only fishes 

 of this group that routinely ate zooplankton. 

 Those consumed by small A. indicus were ostra- 

 cods and small copepods, generally similar to the 

 diet of Vinciguerria nimbaria. The juvenile T. 

 dentex, which were larger than the planktivorous 

 stages of A. indicus, had eaten mostly large cala- 

 noids and small euphausiids, essentially the 

 same eaten by similar-sized Gonostoma spp. In 

 both species, however, the incidence of relatively 

 large prey was as high in the small planktivorous 

 stages as in the sizes which ate only large prey. 

 Thus, rather than changing with growth from 

 small to large prey (but of the same range of rela- 

 tive size), these species appear to prey on an in- 

 creasingly narrower range of relative sizes of 

 prey. 



Most of the nekton-eating stomiatoids were 

 principally or exclusively piscivorous. The Pho- 

 tostomias spp. were the only ones that never ate 

 fish. The relatively large prey of juvenile A indi- 

 cus and A. "cyaneus" were euphausiids, but there 

 was limited evidence that adults of both species 

 are piscivorous. The smallest size group of 

 Chauliodus sloani and all sizes of T. dentex had 

 eaten some relatively large euphausiids or serge- 

 stids; usually these were relatively smaller than 

 the fishes eaten. Otherwise, crustaceans were 

 either a minor or suspect part of the diet. 



The systematic examinations of fairly large 

 numbers of specimens by Beebe and Crane 

 (1939), Legand and Rivaton (1969), and Borodu- 

 lina (1972), and many other isolated reports in 

 the literature generally agree that species of the 

 six families considered as nekton-eating here eat 

 primarily or exclusively relatively large prey 

 which are usually fish. The only well-documented 

 exception is Tactostoma macropus, which ap- 

 pears to eat only euphausiids and sergestids 

 (Borodulina 1972). Notes by Fitch and Laven- 

 berg (1968) indicate that off California several 



congeners of piscivorous Hawaiian species rou- 

 tinely eat crustaceans and that one, Bathophilus 

 flemingi, eats "small crustaceans almost exclu- 

 sively." The discrepancies may be artifacts due 

 to differences in towing speed (not given by Fitch 

 and Lavenberg and most other studies). The 

 same types of differences were observed between 

 specimens from the same area collected at speeds 

 of over or under ca. 1.5 m/s (see Methods). 



There was evidence of selectivity by the preda- 

 tors among the potential prey fishes. All but one 

 of the fishes identified from stomachs were ver- 

 tically migrating species; in particular, the non- 

 migrating Cyclothone and Sternoptyx, which are 

 abundant within the day depth ranges of the 

 predators, were absent from the diets of all pred- 

 ators except Heterophotus ophistoma. Other 

 stomiatoids, particularly the abundant Vinci- 

 guerria spp., were underrepresented, and the 

 abundant myctophids of the L. niger complex 

 were absent. Based on the relative abundances of 

 different migrating fishes in the study area 

 (Table 9), several species of predators took cer- 



Table 9.— Relative abundance and estimated average biomass 

 (wet weight) of vertically migrating fishes based on data from 

 58 oblique trawls taken at night near Oahu, Hawaii, in 1977- 

 78. Total number of fishes caught was 14,084. Relative abun- 

 dance is expressed as percent of total myctophids, the domi- 

 nant group. 



:um 



