Occurrence of Young Billfishes in the Central Pacific Ocean 



WALTER M. MATSUMOTO and THOMAS K. KAZAMA' 



ABSTRACT 



Plankton and other net-caught samples collected on past cruises of the National Marine Fisheries 

 Service, Honolulu Laboratory vessels in Hawaiian and central Pacific equatorial waters were examined 

 for billfish larvae and juveniles. Of the 342 billfish young found in 4,279 net tows, 209 were blue marlin, 

 Makaira nigricans, 82 were shortbill spearfish, Tetrapturus angustirostris, 2 were sailfish, htiophorus 

 platypterus, 20 were swordfish, Xiphias gladius. Twenty-nine larvae were unidentified owing to excessive 

 damage. A preponderance of the catches was obtained from hauls made at the surface during daylight. 



In the equatorial central and North Pacific larvae of only three of the six billfish species nominally 

 found in the Pacific were taken. The captures of these larvae (blue marlin, shortbill spearfish, and 

 swordfish) fill the gaps in the known distribution of istiophorids and swordfish, and extend their distribu- 

 tion eastward to the Hawaiian Islands in the North Pacific. The two sailfish larvae were taken in New 

 Hebrides waters ui the western South Pacific. 



The absence of striped marlin, Tetrapturus audax, larvae in Hawaiian waters was significant, since 

 this species comprises nearly 82% of all istiophorids taken on the longhne in the Hawaiian fishery. Their 

 absence suggested that the striped marlin in Hawaiian waters probably migrate elsewhere to spawn. If 

 this is true, then the spawning habits of this species differ significantly from those of blue marlin. A 

 similar situation could hold for sailfish also. 



In recent years fishery workers have given more 

 attention to the early hfe history of billfishes, owing 

 to the increasing importance of these fishes in the 

 commercial and sport fishing catches. The billfishes 

 in the Pacific Ocean are represented by two 

 families: Istiophoridae and Xiphiidae. The Is- 

 tiophoridae includes five species: Istiophorus 

 platypterus, sailfish; Tetrapturus angustirostris, 

 shortbill spearfish; T. audax, striped marlin; 

 Makaira nigricans, blue marlin; and M. indica, 

 black marlin. The Xiphiidae is represented by a 

 single species, Xiphias gladius. swordfish. Larvae 

 of all these species, mainly from the western 

 Pacific, have been identified and reported by 

 Japanese workers. 



This study, based on larvae collected on past 

 cruises of the National Marine Fisheries Service, 

 Honolulu Laboratory (HL) vessels in Hawaiian and 

 central Pacific equatorial waters, verifies the iden- 

 tifications reported by Yabe (1953), Yabe et al. 

 (1959), Ueyanagi and Yabe (1959), and Ueyanagi 



'Southwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, Honolulu. HI 96812. 



(1959, 1962, 1964), and extends the distribution of 

 larvae of certain billfishes eastward through the 

 central Pacific. 



IDENTIFICATION OF LARVAE 



The three species of istiophorid larvae in our col- 

 lection, blue marlin, sailfish, and shortbill spearfish, 

 were easily identified on the basis of black pigmen- 

 tation (Ueyanagi, 1963) on more than half the length 

 of the lower jaw (sailfish) and on the branchiostegal 

 membranes (shortbill spearfish). Larvae of blue 

 marlin lacked this pigmentation. Since larvae of 

 striped marlin also lack this pigmentation, the sep- 

 aration of blue from striped marlin is most difficult. 

 Ueyanagi (1963) lists two main characters by which 

 he separates the larvae of these two species: (1) the 

 tip of snout either level or below center of eye 

 (striped marlin), and (2) the "anterior edge of orbit 

 projects forward" (blue marlin). The first character 

 is highly subjective and lacks a clear definition of 

 reference points. Even a slight distortion in the 

 body can effect a change in the position of the eye 

 relative to that of the tip of snout. The second 



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