Albacore Studies. I. Size Composition of 



Albacore Taken in the North Pacific During 



the Period of Southward Movement* 



By 



Aklra Suda 

 Nankai Regional Fisheries Research 

 Laboratory 



/English title and summary/ 



Studies on the Albacore - I. Size Composition 



in the North Pacific Ground Between the 



Period of its Southward Migration 



The distribution of the Albacore in the 

 North Western Pacific extends fronn the 

 Equator area to near the Polar Front Area 

 However the fish distributes in such vast area, 

 the fishing grounds are limited almost in the 

 seas between the Subtropical Convergence and 

 the Polar Front, namely in the waters of the 

 North Pacific Current and the north part of the 

 Kuroshio Current. 



This fish is caught mainly by the rod and 



line with live baits in the season between the 



Spring and Summer, but it is caught mainly by 



the long-line in the season between the late 



Autumn and the early Spring. The fishing 



grounds in the former season moves from 



south to north, and on the contrary, the grounds 



moves southward from nearly 40''N. to as far 



o o 

 as 27 -28 N. in the latter, and then seem to 



turn back. 



The present author attempted the analysis 

 of the size composition of the fishes which are 

 caught in the latter season, and obtained the 

 result as following. 



1) Six different size groups appear in 

 every year. When these six groups are hy- 

 pothesized to correspond to each other in 

 every year, the modal lengths of the five sea- 

 sons between 1948 and 1952 are placed with 

 nearly the same intervals as ca. 57cm, 67cm, 

 78cm, 89cm, 100cm, 110cm. 



2) Two groups with the modal lengths 

 78cm and 98cm, are far more abundant thzui 



*PubUshed in 1954 in the Bulletin of the 

 Japanese Society of Scientific Fisheries 20(6): 

 460-68. Contribution No. 63 of the Nankai 

 Regional Fisheries Research Laboratory. 



the others. So far the data obtained, it is 

 clearly recognized that these two dominant 

 groups appear alternately in every other, 

 namely group with the modal length of 78cm are 

 most abundant in the even number years and the 

 other in the uneven number years. 



/end of English summary/ 



Introduction 



The distribution of albacore in the northwest 

 Pacific extends over broad areas from the Equa- 

 tor to the Polar Front. However, mass occur- 

 rences are limited to the north side of the Sub- 

 tropical Convergence, a part of the Kuroshio, 

 and the area of the North Pacific Current. In 

 recent years there has been a gradual Increase 

 in the landings of albacore in Japan from the 

 southern hemisphere, but the greater part of 

 the landings still come from these areas. The 

 albacore fishing in these areas can be divided 

 into two fishing seasons of different character. 

 One is the pole-and-line fishing season for 

 schools moving north from April to July, and 

 the other is the longline fishing season for 

 southward moving schools from November to 

 April. 



With regard to the size composition of the 

 pole-and-line-caught albacore, we already have 

 the reports of Uno (1936a, b). For the size 

 composition of the longline -caught albacore 

 there is the report of Nakannura, Yabuta, euid 

 Kamimura (1953), and the aim of the present 

 paper is to take up where they left off and at- 

 tempt to analyze the albacore size composition 

 of longline catches from the above-mentioned 

 sea areas over the 5-year period from 1948 to 

 1 952. Consequently, pole-and-line-caught fish 

 are completely excluded. From November on, 

 the albacore longline fishing grounds move 



south from month to nnonth. In March their 



o o 

 southern margins reach 27 -28 N. , the south- 

 ward movement stops, and there is a transition 

 to the period of northward migration. In order 

 to limit the material summarized here to alba- 

 core of the southward migration, fish taken in 

 March and thereafter are excluded. During this 

 period, at least, little change can be detected 

 from month to month in the positions of the 

 modes in the size composition. Albacore taken 

 in the waters to the west of the Izu and Ogasa- 

 wara archipelagos have been excluded, and 

 only albacore taken between 140 E. and 180 

 on the north side of the Subtropical Convergence 

 have been considered in this study. 



