in large numbers just when the blue marlin are least 

 abundant. Striped marlin show a tendency to have 

 more than one annual peak in abundance. 



There are several explanations lor the fact that the 

 abundance of these two predators is generally com- 

 plementary. Perhaps they respond differently to 

 some environmental factor, such as temperature. 

 Another explanation concerns the food supply of the 

 two species. As shown earlier, blue marlin feed 

 largely on tuna whereas striped marlin eat a variety 

 of small fish. The seasonal abundance of skipjack 

 tuna is also shown in figure 3. The similarity of the 

 curves for blue marlin and skipjack tuna indicates 

 that fluctuations in blue marlin may be related to the 

 presence of their prey. 



Spawning 



The data on billfish reproduction are few. Male 

 blue marlin with freely flowing milt (sperm) were 

 captured in the central Pacific from February through 

 October. Specimens of striped marlin in the central 

 Pacific had enlarged gonads in February and March. 

 Sailfish spawn in July off Hainan, and from April to 

 August in Formosan waters. The shortbill spearfish 

 is reported to spawn in November and throughout the 

 year but most actively in winter. The broadbill 

 swordfish is thought to reproduce in the tropics, and 

 it is possible that the adults normally inhabit waters 

 cooler than the spawning grounds. Black marlin 

 apparently spawn between June and November in 

 broad areas of the Indo-Pacific. 



Early Life History and Growth 



The young of the billfishes have received enough 

 attention recently to make it possible to distinguish 

 the postlarval and juvenile stages of the several 

 species. Figure 4 is a reproduction of a Japanese 

 scientist's drawings of young billfishes. 



Figure 4 This drawing shows a blue marlin larva 

 less than '/« inch long. It is adapted from " Methods 

 for identification and discrimination of the larvae of 

 five istiophorid species distributed in the Indo- 

 Pacific," by the Japanese scientist Shoji Ueyanagi. 



