Islands axound 30 N. , in the Kinan sea area, and farther north in the Hyuga Nada. Because they 

 make their appearance within a short time and then move away somewhere within a short time, 

 the peak in the catch rate at this season is extraordinarily sharp. 



In the second type of pattern the schools gradually become more concentrated in a 

 connparatively limited area and the schools so formed move andniigrate comparatively slowly. 

 Examples of this type are the spearfishes which appear around Formosa in the winter, the black 

 tuna around Tanegashima, the albacore of the Kinam sea area, the broadbill of the northeastern 

 sea area, and the albacore of the central North Pacific. In this type the center of the fishing 

 grounds does not n-iake any very violent shifts, and the catch rates gradually increase with the 

 passage of time £ind then gradually decline. Consequently in this type it seems as if the schools 

 congregate successively in one sea area after another, and the center of the grounds moves 

 comparatively slowly with the passage of time. As a result, it is easier to follow the paths of 

 migration of the schools in this cas^ than in the former type, and the slopes of the seasonal 

 catch rate curves in a given area are connparatively gentle. 



It is impossible at present to give a full explanation of the relationships between the 

 ecological significance of these two types and oceanographic conditions, however, on the basis of 

 what data we have it appears that the former is related to spawning while the latter is more deep- 

 ly related to food hunting. Accordingly, the former is to be thought of as the spawning season 

 type of migration jind the latter as the food-seeking type of nnigration. However, in many cases 

 it is difficult to draw the line clearly between these two types and opinions will differ on where to 

 establish the criterion. Furthermore, more data are necesseiry in order to establish clearly 

 whether or not these two types actually exist, and it goes without saying that we can arrive at no 

 conclusion without further research. 



Thus we can under the present conditions do nothing concrete about the biological and 

 oceanographical essentials and their theoretical analysis, but from the point of view of the com- 

 mercial fishery it can be innagined that these two types will have a rather important significance. 

 It may also be thought that they would be highly significant from the point of view of population 

 studies, and we feel keenly the necessity for tagging studies to trace the paths of migration, 

 morphometric studies, more complete fish catch statistics, and thorough studies of the spawning 

 and feeding habits of the fish. 



VU. Conclusions 



1. Data from past surveys covering about 20 years have been gathered and worked 

 up. There are omissions because of the author's inability to obtain Sonne of the past data. 



2. An attempt has been made on the basis of these data to clarify the character of 

 the tuna longlining grounds of the eastern Indian Ocean and the western Pacific. 



3. A description in brief has been given of the existing tuna and spearfish fisheries 

 and a discussion has been made of the character of the tuna fishery. 



4. Tuna grounds hitherto had been discussed in terms of total catch and number of 

 vessels operating, but this method leaves the relationship between fishing effort and catch un- 

 clarified. In order to explain this relationship the number of hooks has been tciken as the unit of 

 fishing effort. The number of fish caught per hundred hooks has been called the catch rate. Con- 

 sequently the fishing grounds discussed in this book are'linnited to the grounds of the longline 

 fishery. 



5. Sea areas have been delimited mainly by longitude and latitude or by topography, 

 the seasonal and geographical variations in fishing conditions have been recorded in terms of 

 catch rates, and the character as fishing grounds of the various sea areas has been discussed. 



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