(2) Schools of mediujn skipjack occur in a hiif^her ratio as one 

 goes toward the more northern areas and in a lower ratio as 

 cn3 goes tovmrd the sea area? to the north and west of Japan, 

 (In the Zunan Sea Ar-ea they make up kk percent of the total 

 catch and Sh percent of the total frequency, ^-rhile in the 

 Satsunan Sea Area they account for about 20 percent of total 

 catch and total frequency) o The schools of large and small 

 skipjack, on the other hand, decrease both absolutely in nunbars 

 and frequency and in their percentages as one goes fartiier 

 north, but in the southern and south-iissstem soa ai'sas they show 

 comparatively high ratioso (3) The nijiaber of fish and the 

 n-Jinbsr of appeai'ances for aedium skipjack as compared to large 

 and small skipjack show their aaximun proportions in tha 

 Hokkai-oanrika Sea Area during the suiriner months of Hay - 

 August, which corresponds to the time when their proportions 

 are at their minimijmi in the southwestern ssa areas <> (h) In 

 September the number of medium skipjack in proportion to large 

 and small skipjack in the Hokkai-Sanriku Sea Area suddenly 

 decreases, while on the other hand, it shov/s a relatively high 

 ratio in the (Zunan) Sats'onan Sea kres.^ « (5) la the Satsunan 

 Sea Area the total catch is highest in May, and^it is than tiriat 

 the large and small fish, -vvhich make up 80 percent of the total 

 number of fish caught, are taken in the greatest numbers, while 

 the other 20 percent of medium fish are most numerous in Septeiri- 

 ber and March, that is, at the beginning and end of the season. 

 The situation in the Nankaido Sea Area cannot be clearly known 

 because of the paucity of data, but some catches era made in 

 April and May, and in them medium and small skdpjack are taken 

 in about tlie same proportions » In the Zunan Sea Area, on the 

 vfhole, June and July are the peak of ti:e fishing season, with 

 July in particular giving the year's maximum catches of all 

 three sizes ~ large, medium, and small o The proportions of 

 medium and small fish are roughly tha 's.ame, but in point of 

 nijmbers the small fish are more than 10 percent more nujnsrouso 

 In the Hcklcai-'^anriku Sea Area tJie ca.tch reaches its maximum 

 in July, and as much as 91 percent is made up of medium skip- 

 jack. If tha average catch for each fishing ground is stated 

 in ter'ms of sizes of fish, the order is small, medium, large 

 for the Satsunan and Zunan sea areas, whdle for the Hokkai- 

 Sanriku Sea Area it is medium, large, smally clear Ij^- showing 

 that small skipjack are scarce in the north and abuiidant in 

 the south. 



Next if we investigate the percentas:es of the xiimibers of 

 fish caught and the number of catches iuada in each sea area in 

 each month throughout the whole fis'ning season in tenns of 



— '' Michitaka Udas Seasonal changes in the body weights of 

 yello'jrbail, small yellowfin, cybiids, and skipjack. Bull. 

 Jap. Soc, Sci, Fish, 1 (3),, p, 128 1932, 



55 



