early August o After that time they gradually fall„ This rise and fall in 

 the water temperature is a necessary condition for the migration of the 

 skipjackc Wien the temperature of the Kuroshic changes in this regular 

 fashion, many schools inhabit its waters arid the period of their stay in 

 Japanese waters is prolongedo When„ on the other hand, the temperature 

 rises and falls irregularly or changes abruptly, the migrations of the 

 schools also become irregular^ and although many schools may be seen in 

 certain localities, the migration as a whole often turns out to be of a 

 low volume o 



On the whole the factor which controls the migrations of the schools 

 is the temperature of the depth at which the fish liveo Favorable 

 temperatures of the surface water are within the range of 19° to 26^ Co 

 There is naturally some variation depending on the area, the range in the 

 northern part of the Northeastern area being 20 - 21°, that in the southern 

 part of the same area 22-23^? Zunan area 23-25'^, Satsunan area 24-26 „ The 

 migrations are predicated on the regular appearance of the usual tempera- 

 ture for the season in each of the areas, the water colorj, chemical com- 

 pcsitionj and so forth being incidental conditionSo 



Section 3 Bait 



In skipjack fishing the first thing to be taken into consideration 

 is the choice of a bait^ The use of a suitable bait is the most vital 

 factor in this fishery. As set forth in the preceding pageSj, the skipjack 

 is hatched and grows up in the South Seas and somes north on a migration 

 in search of food. In general when fishes from the South Seas go north, 

 they tend to seek foods which resemble those to which they are accustomed 

 in the South. This probably is instinctive in the fish„ The following 

 is an account of the foods found in the South Seas area. 



(a) tarekuchi iwashi /"probably Engraulis heterolobus Ruppell_7 "■" The 

 body is flattened laterally.. The fisn occur in shallows where the water 

 is less than cz.e fathom deep on coasts where fresh water enters the sea 

 and where msv;..^ove trees grow densely in the vicinity. They school 

 together with the maiwashlo 



(b) mai washi /"may be Harengula moluccensis Bleeker_/-= About 3o6 inches 

 in length, they concentrate in the shade of trees along the shore„ Those 

 which occur near shore are particularly flattened laterally^ The oba 

 iwashi . which are 4„8 to 6o0 inches long, are not seen along the shore but 

 o'.oar in deep water. They differ somewhat from the maiwashi of Japan „ 



<^) urume iwashi == They do appear along the shore but are found in waters 

 of about 10 fathoms depth. The head resembles that of the barracuda, the 

 body is silvery, and the eye is large. The flesh is white and soft, and 

 the fish are hard to keep aliv8o 



(<^) shirotare i was hi =- The shape of the head resembles that of the 

 tarekuchi iwashi^ but the fish is white and has one golden stripe along 

 its sideSo This spe^iies is not seen near shore in shallow places^ It 

 forms dense schools and is suitable for use as bait. The scales are thin 



23 



