regions of the Pacific and Indian oceans are examined 

 in section 5.41. 



Seasonal variations in available stock are marked. 

 See 2.22 on differential distribution. Kume and 

 Joseph (1969a) have shown that there is a threefold 

 seasonal fluctuation in CPUE for the various regions 

 in the eastern Pacific. 



4.23 Average density 

 No data. 



4.24 Changes in density 

 No data. 



4.3 Natality and Recruitment 



4.31 Reproduction rates 



Annual egg production rates have not been es- 

 timated. Little is known of fecundity relationship 

 with fish size. See 3.15 for some estimates. 



Nothing is known of survival rates of eggs and lar- 

 vae because they are so rarely collected. 



4.32 Factors affecting reproduction 

 No data. 



4.33 Recruitment 



There is little information pertaining to the varia- 

 tion in annual recruitment (see 3.43 and 4.24). 



4.4 Mortality and Morbidity 



No work has been done on mortality rates or causes 

 of mortality. 



4.5 Dynamics of Population (as a Whole) 

 No work has been done. 



4.6 The Population in the Community and the 

 Ecosystem 



There is no specific information on this subject 

 available; some general information on distribution 

 and life history is presented in sections 2 and 3. 



5 EXPLOITATION 



5.1 Fishing Equipment 

 5.11 Gear 



Virtually all of the commercial catch of striped 

 marlin is by longlining. The harpoon fishery for 

 billfishes is responsible for less than 5% of the total 

 catch. 



The longline gear aims largely at tunas and 

 billfishes which are distributed at depths of around 

 100-150 m. The gear consists of mainline, float lines, 

 branch lines, hooks, and buoys. The construction of 

 the longline gear differs according to the species of fish 

 sought, but Morita (1969) presents an example of a 

 "standard" gear (Table 6). Several hundred of these 

 units (each unit is referred to as a "basket") are joined 

 in a series to make up a set. The gear is retrieved with 

 a longline hauler. 



Suda and Schaefer (1965) gave examples of the 

 various types of longline gear presently in use (Table 

 7), and indicated that types 1 through 5 are the more 

 typical ones in use. They also included the estimated 

 hook depths for the different types of gear. 



Billfishes are generally found closer to the sea sur- 

 face than tunas. Therefore, in fishing primarily for 

 billfishes, the longline gear is modified by shortening 

 the float line and the branch lines and also by adding 

 another buoy in the middle of the mainline section, 

 the latter bringing the hooks closer to the surface. 

 Furukawa et al. (1957) reported that for fishing 

 billfishes in the East China Sea, the combined length 



Table 6. — General form of tuna longline. (From Morita, 1969.) 



'Length per one basket. 

 ! 1 sun = 3.03 cm. 



150 



