The fact that the density of distribution of the resource is low in terms of fish per 

 tinit of area is not an advantageous condition from the standpoint of the fishery. If the tunas and 

 spearfishes led a sedentary existence with a low density of distribution, they would be difficult 

 to catch and they would have an entirely different significance as the objectives of a fishery. 

 However, they do not live in this way, but rather form schools and migrate and the fishery is 

 established by utilizing this migratory character. Furthermore, the location and nature of the 

 fishing grounds and fishing seasons are naturally determined by these migrations. Unfortunately, 

 our knowledge concerning this migratory character is as yet extremely inadequate, and we cannot 

 utilize this chatracteristic fully, this being the greatest reason for the lack of stability in the tuna 

 longline fishery. The number of species which make up the resource of the tuna fishery is rather 

 large. We have not yet reached any solution to the problem of whether each of these species is a 

 single stock or whether there are a number of independent stocks in the Pacific and Indian oceams. 



There are some people who think that each of these species which is distributed 

 throughout the whole Pacific Ocean is a single stock and that at some time in their lives all of 

 the fish of each species migrate into Japanese waters. The migrations into Japanese waters 

 occur each year at about the same season and are made up of fish of about the sanne size each 

 year. Considering only these facts, it may be thought that this theory is correct. However, 

 when we consider the extent of the Pacific Ocean, there are some facts which give rise to doubts 

 concerning the above opinion and we know of some phenomena which can be thought to indicate the 

 existence of distinct races. 



The solutions to all of these problems must await future research, but they are prob- 

 lems which must be solved in order to determine the character of the resource. 



Dr. Tauchi— has studied the effects of fishery on the stock and has reported that the 

 catch rate for the tunas in Japanese waters ranges from 10 to 55 percent— , varying with the 

 species and among various age groups within a species. In every case he gives rather high 

 values. However, as was mentioned earlier, there is doubt as to whether or not all of the tunas 

 necessarily at some time in their life migrate into Japanese waters, eind therefore even though 

 Dr. Tauchi's values may correctly show the catch rate in Japanese waters, it is naturally doubt- 

 ful whether the tunas of the whole Pacific are being caught at catch rates like those cited above. 



If we consider the relationship between fishing effort and catch in the past, based on 

 statistics of the Ministry of Agriculture and Forestry, the Colonial Office, and the Formosa 

 Fisheries Experiment Station, we cannot perceive any very clear correlation. It appears that a 

 tendency toward an increase in the catch with an increase in fishing effort can be detected, but 

 we can see conspicuous fluctuations in the amounts of the catch from year to year. 



Statistics showing fishing effort are almost entirely limited to the number of vessels 

 engaged in the fishery and their total tonnage and therefore the fishing effort is shown by de- 

 duced values which do not make very good data. Figure 8 shows the total catch, the number of 

 vessels engaged, and the total tonnage of the vessels for the period from 1930 to 1940. The 

 graph shows index figures with 1930 as 100. It can be seen from the figure that the increase in 

 the size of the fishing vessels from 1934 on was very conspicuous. 



11 Tauchi, Morisaburo. 1940. Bull. Jap. Soc. Sci. Fish., Vol. 9, No. 4, pp. 133-135, 136- 



138, 139-141. 

 3/ Catch rates here mean the proportion of the stock represented by the total catch. 



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