driftwood-associated schools 5, wlti?. a sicall rsmainder being 

 shark-associatedo The naxdoer of fish -:.&i-.*in lor each sdiocl 

 sighted (table h) ia the HokJcai-SariTiku Sea Area, is greatest 

 for shark-associated schooi.s follcTOd bj drlftisrccd-iand whsls- 

 associated schools o In the Ztman Sea Area tna catch is greatest 

 from bird-associateds sedentarys ^^^ utiassoclatad schools ; like- 

 viTise in the Sats^Ansji Sea Irea the biggest satchss cons fi'oia 

 bird-asdD slated and d-'iftwc-od-assosiated schools^ followed by 

 those associated ■srlth sharkSo If j, in order to see in greater 

 detail the difference betweesn northern and southern grcundsj we 

 look at tiie total number and percentagas of appearances for 

 each 1''' of latitude, as shcsm in table 5"? "^Q SQQ that shark- 

 associated schools are located farthest ncrth viri.th uaasscoiated, 

 whale-associatedj bird^associated (drirt7.rcod"a5?ociated) 5 and, 

 sedentary- schools ranging in that order from north to scuthoi^/ 

 IMs distribution results from tiie fact tliat the objects with 

 which the schools ai-s aoscciated differ among themselves in 

 their distribution because of oceanographic conditionSj and it 

 is thought that as the skipjack schools move into the Trarious 

 sea areas they succeasivsly associate thsaselrss Trlth different 

 objects o 



Table 6 gives the results of an investigation of ths 

 density of the schools aad how well the fish bite^' » In the 

 Hokkai-Sanriku Sea Area all types of schools except those 

 associated with birds appeai" more often as "dense" than as 

 "sparse," On the other hand, in the Zunan end Sg,tsunan sea 

 areas the number of sparse schools appearing -was greater for 

 all tjTjeso In otjisr words, in the Hokkai-Sanriku Sea Area 

 the proportion of dense schools was markedly greater tiLan in 

 other areas, snd consequently the index of density calculated 

 from it is ^so highero Vfith regard to biting quslitiesj, it 

 appears that in the Zunan and Satsunan sea areas •radent.sry 

 and bird-associated schools bite comparatively ^eZl^ while in 

 the Hokkei-'Sanriku sea as'ea shark-and bird-^associated schcols 

 bite comparatively weilo Eia problem of the density of schools 

 and their bitir<g qualities has mas^j points which must be clari- 

 fied by future in^festigaticnso Since it appears that the spawn- 

 ing and nursery grounds of the skipjack are in this southern 

 areas ^ it may be wondered whether the migration into the Hokkai- 

 Sanrik"u Sea Area is not made with the objective of hunting foodo 

 The greater member of times that the schools take the bait 

 poorly as compared to the Satsunan Sea Area, dsspite the greater 

 proportion of dense schools , may possibly be due tc the abundance 

 of natural food in the northo The greater number of dense schools 

 in this sea area is probably due to special ocaanographic condi- 

 tions in that there are conspicuous current boundai'ies resulting 

 from Trvater of the cold current system barring the advance of the 

 water of the warm current system.o 



The order of the indices of dansity 3r).d Idtirjig shown in table 

 6 differ 3 from that giver, ir, ref e;rencs5/ „ In the present 

 study the statistics c-ivered a larger number of schools 5 

 however, decision oh this point is reserved to th3 futureo 



.60 



