JAPANESE ALBACORE AND BIGEYE TUNA SIZE COMPOSITION STUDIES 



Translated from the Japanese language by 



W. G. Van Campen, Translator 



Pacific Oceanic Fishery Investigations 



U. S. Fish and Wildlife Service 



Honolulu, T. H. 



Size Composition of Albacore and Bigeye 

 Tuna of the North Pacific Fishing Grounds* 



By 



Hiroshi Nakamura, Tadao Kamimura, 



and Yoichi Yabuta 



Nankai Regional Fisheries Research 



Laboratory 



/English title and summary/ 



Size Composition of the Albacore and Big- 

 eyed Tuna Caught in the North Pacific Area 



1) The data upon which this report is 

 based have been obtained during the two 

 periods, viz. , Nov. '48-March '49, and Oct. 

 '49-March '50. The fishes measured were 

 taken exclusively by the longline. The length 

 given in this paper is the so-called fork 

 length. The North Pacific Area, in this paper, 

 is the seas north of 26 N. , between 130°E.- 

 170°W, 



2) As shown in fig. 1, the most dominating 

 size of the albacore is from 60 cm. to 110 cm. 

 in length; the min. is 41 cnn. and the max. is 

 119 cm. in both periods, while the donninating 

 size of the fish taken by rod and line is be- 

 tween 70 cm. and 90 cm. , as shown in fig. 2 

 (after Uno). 



Such large-sized ones as those taken by 

 long-line are nnore variable in length than 

 those taken by rod and line. The difference in 

 size composition of both catches is thought to 



♦Contribution No. 12 of the Nankai Regional 

 Fisheries Research Laboratory, published in 

 1953 in Contributions of Nankai Regional 

 Fisheries Research Laboratory, No. 1. 



Translator's note : The literature citations 

 for the six papers in this collection have been 

 combined and amplified and will be found at 

 the end of this report. 



be due to the difference in the fishing methods, 

 seasons and grounds. 



3) It is recognized clearly that there is a 

 remarkable difference in the size composition 

 of both periods, namely, the nnode C in the 

 former period is perfectly in discord with the 

 mode B and D of the latter period; and the nnode 

 E and F, which appear clearly in the former 

 period, are quite indistinct in the latter, 



4) We explain the phenomenon mentioned 

 above as follows: 



a) The difference in length is caused 

 by the annual difference of the growth. 



If it is assumed that the fishes 

 migrating in a certain sea in a certain 

 season are always composed of the 

 definite age groups, then the mode A 

 and C are composed of the X-age and 

 (X + l)-age group respectively. On 

 this supposition, the fish forming the 

 mode B must be the remarkably well- 

 grown group of the X-age, or the quite 

 undergrown group of the (X + l)-age. 

 It is known in some cases of the fresh 

 water fishes that their annual growth 

 is greatly affected by the environmen- 

 tal conditions. If this holds true with 

 such pelagic fish as albacore, it may 

 be said to be an interesting phenomenon, 



b) The difference in length is caused 

 by the difference in the annual 

 propagation. 



On this supposition, modes A, B, 



C, F are thought to be formed by 



the X, (X + 1), (X + 2), (X + 5)- 



age group respectively. The reason 

 why the modes are, or are not, formed 

 for respective years, may be con- 

 sidered to be due to the difference in 

 the propagation fronn year to year. 



c) The difference in length is caused 

 in the difference of the course of the 

 migration. 



