Report of Investigations of Skipjack and Tuna Resoxirces in 194.7 



Nakamura Research Staff 



A number of studies of skipjack were made during this year. No Investigations 

 of tuna could be carried out because of the inadequacy of research vessel facili- 

 tiesc 



Part I iB a study of the catch from the waters off Oraaezaki, while Part II 

 consists of data on the fishing ground3 of the Satsunan Area which viere collected 

 at Aburatsu. 



I Morphometric Data on Skipjack (KatBuwjnus pelamis) from the 

 Waters Adjacent to Omaezaki 



Between August and the middle of October of 1948 length and weight data were 

 collected on about 1,200 skipjack taken from the waters adjacent to (in the vi- 

 cinity of 30 miles SSW of) Omaezaki in Shizuoka Prefecture, On about 60 of these 

 specimens fin ray counts, gill raker counts, and sixteen other determinations were 

 made. The measuremente were made along a straight line between two points by the 

 use cf calipers, and readings ^jare taken to the nearest millimeter. The body 

 length used was the fork length, that is the straight line distance from the tip 

 of the snout to the point of intersection of the posterior edges of the upper and 

 lower lobes of the caudal fin. The data on the fork lengths and the body weights 

 are shown in Table 3o According to the fishermen the fish which are taken in 

 August and September are either fish resident on ahoals or are members of north- 

 bound migratory schools, while the fish taken in October are from schools which 

 are moving southward. The data shown in Tables 1 and 2 (Table 2 shows only a part 

 of the measurements) have been combined on the assumption that all of the fish be- 

 longed to a single ecological and taxonomic group, that is to say, they show only 

 their characteristics as Katsuwonus pelamis . The following cautions are given 

 with regard to the data in Table 1, Depending on the individual, the most posterior 

 spine of the first dorsal may be completely separated from the spine anterior to 

 it with no membrane visible between the two spines. It is not dear at present 

 irtiether this is an individual variation or whether it is the result of damage 

 to the fin membrane. Again depending on the individual fish, it is difficult in 

 many oases to distinguish the first dorsal finlet from the rays of the second 

 dorsal fin, and since the same difficulty is encountered with the anal flnlets 

 and the rays of the anal fin, the number for both of these counts can be found 

 more accurately on these specimens by adding together the counts for the fin rays 

 and the flnlets. In the case of the gill raker count, also, it would be moat 

 suitable to count the upper and lower limbs sepaa^ately, but in actual practice this 

 is almost impossible and so the figures given represent the sum of the gill rakers 

 on both limbs of the arch. (Persons who carrted on the Investigation — Katauao 

 Kuronuma, Takeichiro Kafuku, and Shoji Kogawa.) 



