X 



UJ 

 Q 



z 



T 



\ I r 



CATCH 

 TONNAGE 

 NO. OF BOATS 



T 



1 — \ — r 



It is considered 

 that both increases and de- 

 creases in the number of 

 operating vessels and changes 

 in the size of the vessels show 

 increases or decreases in the 

 fishing effort. It is not, how- 

 ever, reasonable to consider 

 these simply as increases or 

 decreases in the fishing 

 effort applied to the same re- 

 source. The reason for this 

 is that in many cases an in- 

 crease in the size of the 

 vessel means an extension of 

 the operating area to more 

 distant fishing grounds and 

 with the change in fishing 

 grounds there is a great pos- 

 sibility that different kinds 

 of fish will be tciken. Fur- 

 thermore, it may also be 

 thought that a shift to more 

 distant fishing grounds will 

 result in a reduced number 

 of operations in the course 

 of a year so that in some 

 cases at least larger vessels 

 do not mean an increase in 

 fishing effort. Consequently this comparison of the total catch of the tunas with the number of 



boats and their total tonnage does not enable us to discuss the correlation between fishing effort 



and the stock. 



200 



180 



160 



140 



120 



100 



1930 



1940 



Figure 8, --Catch in relation to number of boats 

 and total tonnage of vessels. 



These factors must nevertheless be thoroughly considered. In figure 8 we can see 

 fluctuations of about 10 percent in the number of vessels, and from 1934 on the total tonnage in- 

 creased sharply. Wide variations from year to year in the total catch can be seen, but through 

 these variations is shown a tendency for the catch to rise. It should be noted that the catch shown 

 here is a total of tunas and spearfishes and does not show any particular species. At any rate, 

 even though some degree of correlation can be detected between the total catch and fishing effort, 

 it may be thought that there are some other factors operating outside this correlation to bring 

 about fluctuations in the catch. The most innportant of these factors are thought to be changes in 

 the migrational pattern accompanying changes in oceanographic conditions and variations in the 

 recruitment to the stock caused by changes in environmental factors. In any case there is some- 

 thing which operates independently of fishing effort to control the variations in the catch, and if 

 the effect of fishing effort on the increase or decrease of the stock can be ignored, it cannot be 

 thought that this condition implies overfishing. 



Overfishing means that the catch exceeds the natural increase of the stock. Deciding 

 whether or not a particular stock is being overfished is an extremely difficult problenn. As far 

 as the resources of the tuna longline fishery are concerned, up to this stage in their developnnent 

 no one has put forward any definite views as to whether or not they are being overfished. 



The danger that the fisheries resource may be overexploited arises from the relation- 

 ship between the reproductive potential and area of distribution of the resource and the effective- 

 ness of the fishing. In fishes which have a high reproductive potential, there is comparatively 



25 



