in Japan must be made for the shortbill spearfish (see 

 2.1). 



5.42 Selectivity 



The longline gear takes fish distributed at a depth 

 range roughly from 50 to 150 m, while the pole-and- 

 line and the purse seine gears catch those living near 

 the surface. For tunas, this means that the longline 

 fishery exploits larger fish than does the surface 

 fishery. 



Concerning the effect of selective properties of the 

 longline gear on growth studies, Suzuki (1971) set 

 forth the following hypothesis and examined the 

 possibility of gear selectivity in connection with Lee's 

 phenomenon: If a fishery exploits fish within a certain 

 size range, the fishery tends to catch larger in- 

 dividuals out of the young fish group whose size is 

 near the lower limit of the selective range of the gear 

 and smaller ones out of the old fish group whose size is 

 near the upper limit. The catches, therefore, tend to 

 represent larger members for the young group and 

 smaller ones for the old group compared with fish ac- 

 tually distributed in the sea. Applying this to the 

 longline fishery, samples from the catch would result 

 in erroneously larger estimates of growth coefficient 

 and smaller estimates of asymptotic length. 



6 PROTECTION AND MANAGEMENT 



Protection and management are the most impor- 

 tant and urgent issues we now face in the world tuna 

 resources. Presently, little attention is paid to the 

 shortbill spearfish stock(s) because it is less important 

 in the commercial and sport fisheries. This, however, 

 does not appear to fix the relative value of the short- 

 bill spearfish in the future management of the fishery. 



7 POND FISH CULTURE 

 Not applicable. 



LITERATURE CITED 



CRAIG, W. L. 



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DE BUEN, F. 



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DERANIYAGALA, P. E. P. 



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DE SYLVA, D. P. 



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1959. Fishing condition of tunas and marlins in the western 

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1963. Some considerations on the growth of marlins, using 

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KOTO, T., and K. KODAMA 



1962a. Some considerations on the growth of marlins, using 

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53 



