6, 

 only 6 were recaptured giving a fishing rats of 50 or ,12. However, „06 is the 

 proportion of the tn.na belonging to the stock which is taken ia one year \7hile 

 .12 is the proportion of the tuna which come in to the Japan Sea side vfhich is 

 taken in one year, and therefore it is hard to malco any cloc6i comparison, but it 

 is thought that both of these valueo are not too fer off. 



Because vrL th species like the black tuna, #iich have a Tjide rangf^ of migra- 

 tion, the course and time of migration probably differ with age, it may happen 

 that older fish are comparatively plentiful or ecarce over a r&ther long period 

 of time, ?.nd it may be difficult to Ljarn the composition of tho stock by study- 

 ing the catch from a limited area. Furthermore a short" term study of the catch 

 frora a rather broad area can hardly ©scape being affected by year-to-year varia- 

 tions in oceanographical conditions. Kevertheless, since there is differmce 

 betT?een the survival rates obtained frora data from various sourcsa, it is prob- 

 ably permissible to make general deductions concerning the stock on the basis of 

 these data. It is therefore probably not too far wronjj to consider that the 

 rates of survival are on the order of .30 for young fish and .75 for aduJLt fieh, 

 and that the catch rate is on the order of .55 for young fish and .10 for adult 

 fieh„ 



Qnotes] 



(l)Kinsure, Kinosuke : Growth Rates of Black Tuna and Yellowfin Tuna as Revealed 

 in the Catch from the Shigedera Fishing Grounds. Bull. Jap, Soc. Sci, Fiah., 

 1 (1). Hay 1932. 



^2)Aika?mj, Hiroaki and Kasuo Kato : Ag® Determination of Piehoa (Preliminary Re- 

 port Ko.l). Bull. Jap. Soc. Sci. Fish., 7 (2). July 1938« 



(3)Ki!5ura, Kinosuke and Kazurai lohii : Fishing Conditions in the Northeastern 

 Part of Suruga Bay (Part 1), On tho Black Tuna and its Young. Bull. Jap, Soc. 

 Sci. Fioh., 1 (5). January 1933. 



{4.)Kawana, Takeshi : On the Relationship Between the Tuna Fishery and Oceano- 

 graphical Conditions. Report of Fisheries Investigations (31) , Warch 1934-, 



(5) Fisheries Kxperiment Station : Appendix to Oceanographic Charts, Fixed 

 Fisfieriee; Pelagic Fisheries, 



^^Accarding to Aikarsa and Kato's data, fish in the 4.0-100 kg group include 

 f}'' ^ " ^ "^ * .05 of th© fourth-year class, all of the fifth-year class, and 

 V?n '° ^i " •''^ °^ *^® sixth-year class. The fish weighing over 100 kg include 

 1 - ,73 a .27 of the sixth-year class and all fish of th© seventh-year and older 

 classes. Therefore if p is the rate of survival, the ratio between large and 



medium fish is 1-p This gives |±^ s ,91 and therefore p s ,655. 



.05^-p+,73p'• ^^° 



If we assume that there are no third=year young tuna included among the small 



adult tuna wsighlng less than 40 kg, since these fish include 1 - .05 s .95 ef 



