South Pacific Ocean (between long. 120°W and 

 180°), this again may be due to insufficient sampUng 

 effort since Gorbunova (1969) showed the presence 

 of larvae in this general area. On the other hand, the 

 absence of larvae along the equator to the east of 

 long. 140°W, and in the waters south of the equator 

 to the east of long. 100°W is probably due to the 

 effect of low temperature waters of the Equatorial 

 Upwelling. Peru Current and the extension of the 

 Peru Current. 



It has been shown by Taning (1955) and Gor- 

 bunova (1969) that swordfish larvae occur in waters 

 with surface temperatures higher than 24°C. The 

 present data confirm these reports since larvae have 

 been found in waters with temperatures ranging be- 

 tween 24.1° and 30.7°C. 



In order to describe accurately the distribution of 

 larval swordfish in the Pacific Ocean, further in- 

 formation is needed from the central South Pacific 

 and the eastern Pacific areas. It can be generalized, 

 however, that the larvae are distributed very 

 broadly in the north-south direction in the western 

 Pacific and distributed more narrowly in the eastern 

 Pacific. This pattern of distribution appears to be 

 governed by the positions of the 24°C surface 

 isotherm. 



As already mentioned, the absence of larvae from 

 the western Indian Ocean was very probably due to 

 insufficient sampling effort, since Gorbunova 

 (1969) showed larvae occurring in waters east of 

 Madagascar Island. In the Indian Ocean, also, it 

 seems that the southern limit of distribution, at 

 least, is determined by the location of the 24°C sur- 

 face isotherm. 



SPAWNING OF SWORDFISH 



To derive some information on the spawning of 

 swordfish, the size composition of larvae collected 

 from the western Pacific in waters between lat. 

 20°N and 20°S was plotted (Fig. 4). This large area 

 was grouped on the assumption that 24°C is the 

 lower temperature limit for swordfish spawning, 

 and since water temperature remains higher than 

 24°C throughout the year in this area. 



Newly hatched larvae, under 10 mm, were taken 

 during all quarters of the year, indicating that 

 spawning is taking place throughout the year in 

 tropical and subtropical waters, at least in the west- 

 em Pacific. If it is true that 24°C is the limiting 

 temperature, then it also follows that if there is any 



u 



z 



o 



Figure 4. — Length-frequency distribution of larval 

 swordfish. by quarters, taken in tropical and subtropical 

 western Pacific Ocean between lat. 20°N and 20°S. (The 

 number of larvae sampled in each quarter is shown in 

 parentheses.) 



spawning in higher latitudes, it would be highly sea- 

 sonal and limited to periods when temperatures are 

 above 24°C. 



The areas of relatively high density of adult 

 swordfish are separate and appear to surround the 

 areas of larval distribution (Fig. 3). They are gener- 

 ally located in the high-laUtude, low-temperature 

 areas. In the Pacific, these areas can be roughly 

 divided into the northwestern Pacific, eastern 

 Pacific, and the southwestern Pacific. Whether fish 

 of different subpopulations occur in these areas is 

 not now clear. Perhaps a more detailed study of the 

 temporal and areal distribution of larvae will con- 

 tribute toward the understanding of the popula- 

 tion structure of the swordfish. 



ACKNOWLEDGMENT 



We especially wish to thank Tamio Otsu of the 

 National Marine Fisheries Service, Honolulu, who 

 read the manuscript and helped us with the English 

 translation. We also wish to thank Kazuko Daito 

 who prepared the illustrations. 



263 



