around Hawaii, in equatorial waters along long. 

 145°W, and in waters of the Trust Territory of the 

 Pacific Islands from 1967 through 1971, and caught 

 juveniles as large as 55 mm. The midwater trawl 

 was usually towed at night for 3-6 h (Appendix 

 Table 1). The area sampled with towed nets is ex- 

 tensive, covering nearly one-half of the Pacific 

 Ocean (Fig. 2). 



A total of 342 billfish larvae and juveniles was 

 obtained from 4,279 net tows of all types. A sum- 

 mary of the catch by type of gear and tow (Table 1) 

 shows that 4,170 tows (97%) were made with the 1-m 

 plankton net, and that of this number 2,850 (68%) 

 were oblique tows. Despite the large ratio of oblique 

 to surface tows (2:1), the catch ratio was just the 

 opposite. The surface tows caught five times as 

 many larvae and juveniles as the oblique tows. 



A closer look at the 1-m net tows by depth and 

 time of day (Table 2) shows that most of the larvae 

 were taken in the upper 1-m of water during daylight. 

 The small numbers taken in the oblique tows suggest 

 that these larvae are restricted to the surface, and the 

 small catches in night tows suggest that these larvae 

 migrate downward at night. Both observations are 

 similar to the results obtained by Ueyanagi (1964) in 

 the western Pacific, where he examined 32 day and 

 31 night plankton net samples from depths of 0, 20, 

 and 40 m. He found that abundance of larvae de- 

 creased with depth during the day, and that the day 

 catches at the surface were greater than those at 

 night. His data point out one other aspect which does 

 not appear in our data: that within the upper 40 m of 



Figure 2. — Localities of captures of young Istiophoridae 

 in the Pacific Ocean. Area sampled by the Honolulu 

 Laboratory indicated by solid line and capture sites by 

 black dots. Localities of captures by Howard and 

 Ueyanagi (1965) shown as shaded areas. 



Table 1 . — Billfish larvae and juveniles collected by various gear from research vessels of the 

 Southwest Fisheries Center. Honolulu Laboratory in the central Pacific Ocean, 1950-71. 



Larvae and juvenile catch 



Gear 



Type 

 of tow 



Number Blue 

 tows marlin 



Short- 

 bill 



spear- 

 fish 



Sail- 

 fish 



Damaged 

 un- 

 Sword- identi- 

 fish fied Total 



Per- 

 cent 



1-m plankton 30-min. surface 1.320 142 68 2 16 22 250 73.1 



net 



1-m plankton 30-min, 40-200m 2,850 25 14 4 50 14.6 



net oblique 



Cobb pelagic 6-h, 20-100m 92 18 18 5.3 



trawl horizontal 



1 x 2 m 30-min. surface 17 24 24 7.0 



neuston net 



Totals 

 Percent 



4.279 209 

 61.1 



82 

 24.0 



0.6 



20 29 342 100.0 

 5.8 8.5 100.0 



240 



