This paper is a result of scr^ stadias wnich I hs.ve srad? of 

 the ecology of j^ip^aok schools j, using rscoris rriade on taa 

 sld-pjack fisLlng gro^jnds by the Hairjo Ilaru of the Fukuchinia 

 Prefecture Fisheries Scpsrimant Stationo In classifying tvpss 

 of skipjack schools, I have fcllc^rsd the procsdure ,of the 

 Fukusiiiraa Prafecture Fisheries Experiment Statiorii/ and of Mto 

 Shin Susuki—' 8 



n^-pes of Schools and Sea Condi ti ens o 



A comparison of the dJ.stributicn of fishing grcands 

 and the distribution of salinities (table 1) shcii^'s that in May 

 and June southeast of the province of Boshu /Cbiba Prefscture7, 

 in a warm current area of high salinity («^-i;-> 25o70) the sain 

 types of schools encountered are those associated ■vclth whales 

 or with flocks of birds, while in July, Aiigust, and Septeraber, 

 in the waters of comparatively low salinity to the north 

 (^]_5<25<.?0)5 tlis only schools seen are those associated tdth 

 sharks or those not associated with anythingo Surface v^ater 

 temperaturss en the fishing grounds are everywhere ro^j^hly the 

 same (21° to 23" C„), but the differential in temperature 

 between the surface and "the 25-nieter leval shows approrxiinately 

 the same distribution as the salinity^ both of them being thought 

 to indicate a diiferencs in current sj^stera (figo l)o Of course 

 the fishing season in the south is in May and J-jiis, while in the 

 north it is in July., August, and Sspterabsro It may be -thought 

 that this is the reason for the greater vertical difference in 

 water temi-rer^ure in ti-ie north, however, in this sea areaj the 

 regular yearly studies also reveal a greater vertical difference 

 in temperature the farther north one goeSoJ''^ This relationship 

 between current gyk terns and types of skipjack cchools can be 

 seen from the records of investigations carried out by the 

 Chiba Prefecture Fisi^^ies Sxperimant Station over a period of 

 three years (figo 2)^-' o 



Talcing the waters off Boshu as a bcundarj'-, it is not clear 

 why there is a difference in the types of slcipjack schools 

 found to the north and to the south. It may be wondered whether 

 this difference is not due to differences in the distribution 

 of the objects with wnich the schools are associated. ti^Ls 

 distribution being affected by oceanographic conditions3/, 

 rather than to differences in the character of the skipjack _ 

 schools theraselveso Suaukii/ defines the unaccompardec scnooxs 

 as those which appear at tiie surface in areas where there are 

 no other objects or signs of life, and bird schools as those 

 which cannot be detected except by sighting flocks of sea _ 

 birds. The sharks are whale sharks, around which the si<apoack 



