affected by physical and biological factors such as, for 

 example, the ocean currents, water temperature, food 

 supply, and predation. 



4.33 Recruitment 

 No information is available. 



4.4 Mortality and Morbidity 

 No information is available. 



4.5 Dynamics of Population (as a Whole) 



Knowledge is limited. See 4.24 for information on 

 apparent abundance. 



4.6 The Population in the Community and the 

 Ecosystem 



Knowledge is very limited and no particular infor- 

 mation is available. 



5 EXPLOITATION 



5.1 Fishing Equipment 

 5.11 Gear 



The tuna longline fishery is essentially responsible 

 for all of the commercial shortbill spearfish catch from 

 the Indo-Pacific areas. The longline gear has been 

 developed to catch tunas, billfishes, and sharks that 

 are more or less sparsely distributed in a depth range 



roughly from 50 to 150 m. The form of the gear set in 

 the water is as shown in Figure 8. 



A single unit of gear consists of the main line, a 

 number of branch lines, each with a hook, the float 

 line and the buoy. The depth at which the hook hangs 

 from the main line can be adjusted by the length of 

 the float line. The construction of the gear differs 

 depending on the species of fish sought, the conditions 

 of fishing grounds and the efficiency of fishing vessels. 

 When aiming mostly at the albacore or a species of 

 salmon shark, as seen in Table 4, the gear ordinarily 

 used by the fishermen has relatively short branch 

 lines with short spacing between them. In such a con- 

 struction the branch lines in a single unit of gear tend 

 to increase in number. With increasing size of the 

 species of fish sought such as yellowfin and bigeye 

 tunas, the length of the branch lines and the spacing 

 between them tend to increase and the number of the 

 branch lines in a single unit tends to decrease. This 

 appears to come from the fishermen's experience in 

 improving fishing efficiency by considering the density 

 of schools of the fish sought, and in preventing the 

 gear from tangling while it is in the water or is being 

 retrieved. The relation between the length of the branch 

 lines and the spacing between them is given in Figure 

 9. 



The length of the main line tends to increase accord- 

 ing to the size of the vessels and the power of a 

 longline hauler rather than to the size of fish sought. 



u 

 z 

 < 



DISTANCE BETWEEN BRANCHES (m) 



Figure 8. — An example of the longline gear: A, buoy; B, main 

 line; C, branch line. (Katsuo-Maguro Nenkan, 1969). 



Figure 9.— Relation between length of branch line and distance 

 between branches (Katsuo-Maguro Nenkan, 1969). 



Table 4.— Longline gear construction by the species of fish sought (Katsuo-Maguro Nenkan, 



1969). 



51 



