schools congregate in fear of spearfisho Among whales 

 accoii5)anied by skipjack sohoolsc, the sei whale id? xost 

 common followed by the fin whalfe„ Floating legs are mainly 

 of tropical origin,, having picked up their accompanying 

 schools while drifting past the shoal fishing gromidso 

 Ccnsequentlyj, according to Susiikip such schools accompanying 

 drift logs are sighted in gr'e^test numbers in the main current 

 of the K-uroshio between the Satsun5.n fishxng grounds and Zunan, 

 such schools being rare within 20Q irdles of the coast„ north 

 of Tokiwao-j;- 



Thusc, skipjack schools associated with birds,, with whales, 

 or with floating logs generally appear in greatest n-ombers in 

 waters of the main Kurosblo sy-steiuj, while schools accompanying 

 sharks appear for the most part in warm water masses of the 

 Northeastern Sea Area where the Kuroshio and Oj'-ashio current 

 systems impinge upon each cthero Schools accompanying whales 

 are said to be hard to find in the southern portion of the 

 KuroshiOo Conseqientlyj the distribution of salinity and dis- 

 tribution of types of sicipjack schools are probably correlated. 



As the schools associate with birds, trees, whales,, or 

 sharks for quite different reasons =■ quite fortuitously in tJie 

 case of the birds ^ in search of rich feed in the case of drift 

 logss and to escape predators in the case of whales and sharks - 

 and the objects with which the schools are associated differ in 

 their size and rate of moYement, it may be thought natural that 

 differences in density and size should ,also arise among these 

 various types of schools „ The following is an attempt to 

 express the degree of density numeracalljo Fist of all,, lor 

 each type of school the maiLber of Hmes of appearanoe of dense 

 schools is indicated by m, the number of times of appearance 

 of sparse schools by n, the concentration in space °f "-"^^^tSf 

 fi=h in the case of dense schools is represented oy the density 

 indi I and in ti-.e case of sparse schools by x 1 x 0)„ There^ 

 fore, the index of average densitv of a school ol fish xs 



k ^ m X 1 " n X x 

 m - n 

 By means of this formula k is caloilated using observed values 

 for m and n and postulating two values and Od for x (table 2), 

 In the case of imaccompanied schools k is !<, for schools accom-= 

 panying whales and sharks it is about O085. for schools accompany- 

 ing birds it is 0»1 or 0»2o 



# Nakayaraai/ also expresses generally t he same idea,, 



72 



