The Time and Duration of Angling and the Catch of "Katsuo", 

 Euthynnup vagaas (Lesson) 



Synopsis /"in Engliah_7 



Bas«d on the data supplied from the fisheries-surveying boats, more 

 than 50 in number, in the /ears from 1936 to 1939| the relations among 

 the time of angling (to), the duration of angling (T) and the catch of 

 Katsuo (n) vyere examined statistically. 



Three maxima shonn- in the catch-curves (Fig.l), I.e. the principal 

 one dominating early in the morning (5 - 9 h. a. m. about after the 

 sunrise), idiich cpvers nearly the half of the total catch in a day, the 

 secondary one falling about after the noon, and the tertiary one in the 

 evening before the sunset, are noticed. Those maxima and the exponential 

 deca,}' indicated in the general trend of the catch curves (Fig, 2) can be 

 interpreted mainly as the results of the behaviour of the shoals of 

 "Katsuo," subjected to their feeding habit, besides the disturbance of the 

 i^als due to fishing, etc. 



As r^tjards to T, the dominant value of the catch corresponds to 10«iU) 

 felautes, and unto 80 minutes df T the catch' increase & with the increaM of 

 7, arid than beyond 80 minutes the catoh falls down rapidly, ^end of English 

 synepsisy 



If wo take to as the time v/hen the skipjack school is sighted and 

 fishing is begun, T as the duration of fishing, and n as the number of fiih 

 taken in the unit time, then the total catch can be expressed as 



t s tfltT 

 N a ^ nAt . The relationship between fish catch and fishing 



t > to 

 time were Investigated statistically from the data obtained from the 

 research vessels of all of the fisheries experiment stations throughout 

 the country and from about 50 skipjack fishing vessels especially dssignattd 

 to mal'.e reports on tlia fishing situation for the four years from 1936 to 

 1939i and the results are reported below. 



(1) Rfllatjionship al t© I j^me ia ^a^^oh n. Figure 1 shows in relation to tg 

 the assembled totals of skipjack token in eaoh hour ^t, the number of 

 catches made at that time, and the number of fish taken per catoh. Looking 

 at these graphs it oan be aeen that not many fish are taken up to about 

 4i00 a.m., but around the "false dawn" at about SiOO the catoh begins to 

 inorease rapidly. The first and principal peak in the catch curve appears 

 between SiOO and 9iOO a.m. and thereafter it falls off sharply, although a 

 seoond snail peak develops around noon to It 00 p.m. (This is thought to 

 eorrespond to what the skipjack fishermen of Shlzuoka Prefecture oall ths 

 "change of shadow.") The oatch then continues to decrease steadily 

 through the afternoon. A third peak corresponding to the time of day called 

 "^oliaftaUSIft'' tppeare to exist at around AtOO to 6iOO p.m., but it is not vtry 

 clear. 



Hbw if wo take Ni as the number of fish caught during the forenoon, 



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