ent and easily available organisms in their habitats. 

 Watanabe (1960) stated that there is no significant 

 difference between the stomach contents of tunas and 

 billfishes except that billfishes feed more frequently 

 on juvenile tunas and billfishes than tunas do. The 

 forage organisms which are the most common in the 

 stomachs of billfishes in the North Pacific Ocean are 

 squid and fishes of the Lepidotidae, Alepisauridae, 

 Acinaceidae, and Katsuwonidae. 



Koga et al. (1972) examined the stomach contents 

 of the shortbill spearfish in the central South Pacific 

 Ocean and pointed out that the number of species of 

 fish eaten by this species is limited compared with the 

 striped and blue marlins, although the food of this 

 species is almost identical with the other marlins with 

 respect to the cephalopods and crustaceans. They 

 noted that the members of the Myctophidae, 

 Triacanthidae, and Polyipnus which are considered to 

 be deepwater dwellers are lacking in the stomachs of 

 the shortbill spearfish. These authors assume from 

 this that the shortbill spearfish swim in a shallower 

 layer of water than do the striped and blue marlins. 



Volume of food eaten during a given feeding 

 period: Information is lacking on the absolute 

 volume of food eaten by this species. Koga et al. 

 (1972) examined the relative volume of stomach con- 

 tents of tunas and billfishes by classifying it into five 

 categories and mentioned that the shortbill spearfish 

 and yellowfin tuna more often have stomachs filled 

 with food than the albacore, striped marlin, and blue 

 marlin do. They also stated that the shortbill spear- 

 fish and albacore tend to eat smaller food items than 

 do the other tunas and billfishes. 



3.43 Growth rate 



Relative and absolute growth pattern and rates: The 

 annual growth rate has been estimated for the Atlan- 

 tic sailfish (de Sylva, 1957), the western Pacific 

 sailfish and striped marlin (Koto and Kodama, 1962a; 

 Koto, 1963) and the black marlin in the South China 

 Sea (Koto and Kodama, 1962b). Age determination 

 using hard tissues such as scales, otoliths, and contra 

 are difficult to apply to the billfishes (Koto and 

 Kodama, 1962a). Information on the absolute growth 

 is lacking for the shortbill spearfish. (For relative 

 growth, see 1.31.) 



3.44 Metabolism 

 No information is available. 



3.5 Behavior 



3.51 Migration and local movement 



Data available thus far are too limited to consider 

 the movement of this species. 



3.52 Schooling 



Composition of stocks by size, age, and sex: See 

 4.13. 



Mixing between schools: Howard and Ueyanagi 

 (1965) mention that the two areas of greatest density 

 of the Pacific shortbill spearfish appear to correspond 

 with the overlapping borders of distribution of striped 

 and blue marlins, and speculate whether, if more data 

 were available, the same might be found for all such 

 areas of overlap between the distribution of striped 

 and blue marlins. For schooling habit, see 3.16 



3.53 Response to stimuli 



No information is available. For response when 

 hooked in the longline gear, see 3.32. 



4 POPULATION 

 4.1 Structure 



4.11 Sex ratio 



According to Nakamura (1944), the sex ratio of the 

 shortbill spearfish and sailfish is nearly 1:1 during the 

 spawning season in waters adjacent to Taiwan. For 

 the swordfish and the striped, blue, and black 

 marlins, the size difference with sex and the seasonal 

 change in sex ratio are noted (Nakamura, 1944; 

 Nakamura, Yabuta, and Ueyanagi, 1953; Ueyanagi, 

 1953). Koga (1959) states that size difference with sex 

 is also evident for the shortbill spearfish in the South 

 Pacific; the female is larger in average length than the 

 male. The catch data collected during 1966-70, 

 however, suggest that the difference in size between 

 the sexes for this species is not so definite as first ex- 

 pected (Koga et al., 1972). The sex ratio from 

 September through November in the South Pacific, 

 according to Koga's data, is 1:1.54 (M:F). The 

 preponderance of females in the catches of this species 

 is also noted in the equatorial western Indian Ocean, 

 although the longline catches are quite few (Merrett, 

 1971). 



4.12 Age composition 



No information is available on age. 



4.13 Size composition 



Size composition of the shortbill spearfish from the 

 Pacific Ocean is reported by various authors (Royce, 

 1957; Koga, 1959, 1967; Kume and Joseph, 1969b; 

 Strasburg, 1970; Koga et al., 1972). The size composi- 

 tion of fish from the Indian Ocean is given by Merrett 

 (1971). Although data on size compositions reported 

 thus far are limited in number and fragmental 

 seasonally, there appears to be a difference in size ac- 

 cording to localities in the Pacific Ocean. As shown in 



49 



