The Distribution of the Larvae of Swordfish, 

 Xiphias gladius, in the Indian and Pacific Oceans 



YASUO NISHIKAWA and SHOJI UEYANAGF 



ABSTRACT 



The distribution of larval swordflsh, Xiphias gladius, was determined on the basis of 325 specimens 

 collected from Japanese research vessels operating in the Indian and Pacific Oceans. These larvae, 

 ranging from 3 to 160 mm in total length, were caught by larva-net tows and by dip netting. 



The larvae are distributed over virtually the entire tropical and subtropical areas of the Pacific Ocean 

 except for the eastern Pacific east of long. 100°W. The northernmost occurrence was at lat. 31°N, long. 

 132°E, near Kyushu in the western Pacific, and the southernmost was at lat. 22°38'S, long. 105°24'W in 

 the eastern Pacific. Data were insufficient to delineate the distribution in the Indian Ocean. 



The surface water temperature in the areas of larval swordfish occurrence ranged from 24. 1° to 30.7°C. 



The distribution of larval swordfish, Xiphias 

 gladius. in the Indian and Pacific Oceans was de- 

 termined on the basis of 325 specimens collected 

 from Japanese research vessels. These larvae were 

 collected largely by larva-net tows and included the 

 26 specimens previously described by Yabe et al. 

 (1959). The results from this study supplement the 

 findings on larval swordfish occurrence in the In- 

 dian and Pacific Oceans by Taning (1955), Yabe et 

 al. (1959), and Gorbunova (1969). The method of 

 collection was as described by Ueyanagi ( 1969) and 

 included surface tows as well as simultaneous sur- 

 face (0-2 m) and subsurface (20-30 m) horizontal 

 larva-net tows. 



SIZE OF THE LARVAE 



The 318 larvae collected by larva-net tows ranged 

 in total length from 3 to 160 mm. Seven specimens 

 taken by dip netting measured 34-80 mm. The 

 length-frequency distribution of 280 larvae taken by 

 net tows is shown in Figure 1. 



A very large proportion of the larvae was cen- 

 tered around the 5 mm length class. The numbers 

 rapidly decreased between 5 and 10 mm, after 

 which they leveled off to about 30 mm. Very few 

 larvae exceeded 50 mm in total length. 



40 60 K) 100 



iotai length 



Figure 1. — Length-frequency distribution of swordfish 

 larvae collected by larva-net tows. 



VERTICAL DISTRIBUTION 



The fact that the larvae of swordfish are distri- 

 buted largely at the surface is well known (Taning, 

 1955; Yabe et al., 1959; Gorbunova, 1969). The ver- 

 tical distribution was further examined for possible 

 day-night differences (Fig. 2). The catches in sur- 

 face (0-2 m) and subsurface (20-30 m) tows were 

 compared through relative densities represented by 

 the percentage of occurrence, as follows: 



Number of surface tows on which larvae were caughl x 100 

 Total number of simultaneous tows on which larvae were caught 



Subsurface 



Number of subsurface tows on which larvae were caught x 100 

 Total number of simultaneous tows on which larvae were caught 



Far Seas Fisheries Research Laboratory. Shimizu, Japan. 



As seen in Figure 2, the density of larvae was 

 greater at the surface both during the day and night. 



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