In this fashion the skipjack spawn and grow up nea" the islands and 

 reefs in tropical waters. These waters are south of 24-° North Latitude, 

 and their surface tempera tuxes are above 20° „ It appears that the skip- 

 jack schools make their permanent homes there and pass the winter there. 

 Within this area they spawn principally at places close to islands and 

 reefs. Besides those which spawn in the South Seas, skipjack with ripe 

 eggs are also taken in the Okinawa and Ogasawara areas. It appears that 

 some skipjack also spawn in those waters. In short, the spawning grounds 

 of the skipjack extend over a rather wide area with the center of spawning 

 activity in the South Seas. 



2, Development of the Skipjack 



(1) The small skipjack stage (weight 3OO-4.OO momme / 39.7-53 o%J, 1-2 

 years old) 



The juvenile fish are slender and thin^ They like to leap about on 

 the surface of the water. They eat mainly schlzopods, amohlpods, larval 

 decapods, and small anchovies. The island-dwelling schools will not 

 come to chum-bait and they are still very timid so that when a ^---cssel 

 approaches them they tend to submerge suddenly. Once they get out into 

 the open sea and enter upon the pattern of migration, however, they 

 gradually come to take the bait better and better. The schools of 

 descending skipjack returning south after the equinox are not skillful 

 in the competition for food and they are liable to have empty bellies, 

 which makes them take the bait very well» 



N ote ; "Descending skipjack" are those which are returning south in the 

 fall after their northward migration, "Water pushing / mizuoshi7 " is a 

 term used to describe the turbulence of the surface where a school is 

 feeding. IVhen they sight the prey, the whole school deploys in a line 

 of foragers and advances through the school of bait with the fish 

 showing their dorsal fins above the surface. The turbulence caused 

 by their tails gives rise to long continuous ripples on the surface 

 which make the area readily distinguishable from, the surrounding 

 waters. 



(2) The luedimn skipjack stage (weight 600-800 momrne / 4. 96-6. 62 lbs^7> 

 age 3 to 4- years) 



These fish are the main element in the skipjack schools which 

 migrate into Japanese waters. Their bodies are perfectly fusiformo 

 They are strongly migratory and rather than take up residence on a shoal 

 or around an island and eat crustaceans, they prefer to swim swiftly 

 -n the open sea hionting schizopods, small fishes, and squid. If they 

 do become attached to a shoal, they do not remain there long. They form 

 large groups of schools and swim through the surface v/aters in orderly 

 and disciplined fashion searching for food. They generally take the 

 bait well. They have already become adept st mizuoshi , and have learned 

 to herd bait and to accompany sharks and whales. At times they also 

 follow floating logs for thousands of miles of leisurely migration. 

 Note: The term "b.: ling / ^c dok auk-or i7" is used to describe the 

 action of the 3kij..^.aCK o:,nool in surrcunding a school of small sardines 



18 



