From the Bulletin of the Japanese Society of Scientific Fisheries, 

 Volo 6,, Noo 1» ppo l>21s, May 1931 o 



(English title and synopsis) 



Notes on the Shoal of Bonito (Skipjack^, Katsuwonus pelamis ) along 

 the Pacific Coast of Japan 



By Hiroaki Mkawa 



SYNOPSIS 



(1) Age of bonito was determined on the basis of the 

 vertebral bones just like that of chub-mackerel. The body 

 lengtl:^/ of bonito well correlates with the length (T) of the 

 centrum of the vertebral bone (fig* l)" The rings (r) formed on 

 the surface of the c en trim can be considered as the year rings o 

 The first ring measures 2o5 nim., in radius c, the second one 3o9 

 mmo, the third one Sok. iiim„5, and the fo^;a"th one 7o2 mmo IBien 

 the body length is 26 cmoj the lengtli of the centrum (T) becomes 

 equal to the radius of the first ring (r^^) and thus the ring may 

 be corapletedo Therefore „ the bonito less than 26 cmo in body 

 length may belong to 0=year group o According to the similar 

 assumption, I»year grot?) ranges in body length from 27 cm to 3U 

 cm,, Il-year group from 3$ cmo to U3 cmo, and m-year group from 

 hh cmo to 53 cmo IV-year group may be larger than $k cm, 

 (2) Most of the bonito cau^t by angling are mainly composed 

 of III" and IV-year groups in the LLu-Kiu region, and Ill-year 

 group oc^pies 6^% of all and IV^year group i;0^. While bonito 

 Ihoal Ts simply composed of Ill-year group in the Tohokji region. 

 It is also remembered that bonito caught by longlines is far 

 larger in size than that by angling and usually belongs to 

 V-vear group or far older oneo (3) lliere are two different 

 shoals of bonito in these regions o The one is the migratory 

 shoal and the other the resident shoal. The resident shoal xs 

 generally larger in tiie mean value and in the modal value of body 

 lengtti than the migratory group either in III»year group or m 

 IV-vear group. The migratory group is siii?)ly composed of 

 TTll-vear group in the Tohoku region, while the resident group 

 compSres'to Lme extent IV^year groupo The -i^^^f 'Jhfirthe' 

 Ser than 20 on the quality»indicator (lo3, W/L^), while ti^e 

 resident group less than 20, In the Liu=Kiu regi on, the 



of CoSerative Studies of the Skipjack Fisheryi 358, 1935o 



32 



