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surface isotherms (Fig. 3) and moves northeastward 

 and southwestward with the seasons. Thus, in the 

 first quarter the larvae were found far south of the 

 island, but in the second quarter they were abreast of 

 the islands. In the third quarter the edge of larval 

 distribution shifted northward a few degrees of 

 latitude past the islands and moved back to just south 

 of the islands in the fourth quarter. The northward 

 shift of the distribution during the four seasons is 

 about 10° to 11° of latitude. 



Ueyanagi (1964) reports that larvae of istiophorid 

 species occur generally in water that is warmer than 

 24°C. Jones and Kumaran (1964) also show that none 

 of their larvae were taken in waters colder than 

 24.5°C. Our data (Appendix Table 1) show that al- 

 though most of the blue marlin larvae were taken in 

 water between 26° and 29°C, the lowest temperature 

 associated with capture was 23.8°C. 



Shortbill Spearfish 



Larvae of shortbill spearfish comprised 24.3% of 

 all billfish larvae collected by us. Their distributional 

 pattern in the central Pacific is similar to that of blue 

 marlin larvae (Fig. 2). North of the equator the cap- 

 tures were grouped around the Hawaiian Islands in 

 an area bounded by lat. 10° and 23°N and long. 150° 

 and 174°W. The area between long. 174°W and the 

 eastern limit of Howard and Ueyanagi' s (1965) data 

 should also contain larvae of this species to show a 

 continuous distribution from the western Pacific to 

 the Hawaiian Islands. Because of inadequate sam- 

 pling, only three surface day tows and eight oblique 

 tows, no larvae were taken there. 



South of the equator, larvae were taken in a band 

 (lat. 0° to approximately 20°S) extending from the 

 New Hebrides Islands through the Tuamotu Ar- 

 chipelago, similar to that for blue marlin. The gap in 

 the distribution along the equator, between lat. 7°N 

 and 5 C S, may be interpreted in two ways: first, the 

 gap could be due to insufficient samples of surface 

 day tows; and second, the gap could represent a 

 separation of the shortbill spearfish into northern 

 and southern populations. The latter is supported 



Figure 3. — Localities of captures of young blue marlin by 

 quarters. Solid lines represent mean surface temperature 

 for last month of quarter. Dashed lines represent surface 

 temperature at time of sampling. Small open circles rep- 

 resent sampling with plankton nets in 1° square area; large 

 solid dots represent capture sites. 



242 



