condition factor between the migratory and sedentary schools is 

 not very great in the third-year fish below k3 cmos but in 

 fourth-year and fifth-year fishj, with the increase in age and 

 body length, the difference becomes well marked (table 5)o The 

 proportions of the mixture of these two groups of fish should 

 probably also be noted as one reason for the fluctuations in the 

 amount of catch in the I^yukyu Sea Areao 



i^o Differences in the condition factor and the manner in 

 which the'^^'take gig bait o (table H). "There are seasonal 

 changes in how well the fish take the baito At the start and^ 

 finish of the season in spring and fall most of the schools bite 

 wellj, but during the peak season few of them do , It is hard tc 

 find any clear correlation between the differences in the water 

 temperature at the oositions Tfhere catches were made and the 

 way the fish biteo \(hexe the schools were dense and large 

 the fish generally took the bait well . and where they were 

 sparse and .small the fish mostly bit prorlyo Perhaps the 

 "panic theory"it/s which explained the relation between herring 

 schools and catchj could be used to explain this circumstance o 

 Furthermore, the sedentary schools with their condition factor 

 of less than 20 generally take the bait well., while the mxgra- 

 tory schoolffj with condition factors of more than 20, generally 

 bite poorlyo In a general view, it may be wondered whether the 

 biological characteristics of a school govern how well or how 

 badly the fish in it biteo 



The Skipjack Schools ot the Northeastern ^a ^ea 



5o Distribution of bo^ lengths ^ ^e compositiono 



The skipjack schools of the Northeastern Sea Area, stretching 

 from the Ogasawara Is. and the Zunan chain to the waters off 

 Sanriku, differ from those of the Ryukyu Sea Area xn that the 

 bodv-length groups are distributed only between U5-55 cmo and in 

 tSt as far Is age groups are concerned, schools of fourth-year 

 fish are abundant and flfth^year fish are extremely scarce ifxgo 3)o 



60 Condition factoro In the Northeastern Sea Area, too, 

 there are~bf5~i?5^iB that differ in their condition factor (table 3, 

 figo 6)0 Thev are divided into migratory schools with an average 

 condition factor of over 20 and sedentary schools ^^^f !, f^^-^°^ 

 less^than 20^ the former are called the Ryukyii stock and the 

 t!!Li +L oksawara stocks The difference in condition factor 

 Stw^en ^e twoToups is more extreme than the difference between 

 Dex.we«a uic o s ^ p^,wii Sea Area.. Consequently it is thought 

 th:t the'relKionsS? bSSn'tSelwo groups of the Northeastern 

 Sef A^ea is even more distant than the relationship between the 

 two groups of the Ryukyu Sea Areao 



Graham, Mo" Jo du Conseil, U (2), 1931o 



k3 



