any time, the use of time for scouting and fish- 

 ing and day baiting should be considered in 

 relation to the daylight hours available. On the 

 basis of 12 hours of daylight, the percentage of 

 time used in scouting and fishing and day bait- 

 ing can be obtained by simply doubling the per- 

 centages given in table 1 for these activities 

 (table 2). 



It appears from table 2 that on an annual 

 basis, a little less than one-half of the daylight 

 hours are spent in scouting and fishing or in 

 day baiting. This situation is considered in 

 more detail later. 



Table 2 . --Percentage of daylight hours spent 

 in scouting and fishing and day baiting by 

 Hawaiian skipjack tuna Vessel A and Vessel 

 B, 1952-53 



Activities 



1952 



1953 Average 



Vessel A 



Scouting and fishing 26.4 

 Day baiting 16 .8 



Total 

 Vessel B 



43.2 



Scouting and fishing 30.2 

 Day baiting 11.4 



Total 



41.6 



Percent 



38.4 

 16.2 



54.6 



37.0 

 14.0 



51.0 



32.4 

 16.5 



48.9 



33.6 

 12.7 



46.3 



FACTORS AFFECTING THE CATCH 

 OF SKIPJACK TUNA 



Factors affecting the catch of skipjack tuna 

 may be considered in three major categories, 

 although this scheme is somewhat of a simpli- 

 fication, considering the interaction among the 

 factors. These categories are (1) the avail- 

 ability of skipjack tuna, (2) the availability of 

 live bait, and (3) the availability of the crews 

 and fishing vessels for fishing. 



Availability of Skipjack Tuna 



As mentioned earlier, the availability of 

 skipjack tuna follows a marked seasonal pat- 

 tern. Table 3 gives the skipjack tuna catch, 

 baitfish catch, and quantity of skipjack tuna 



landed per pound of bait as a monthly average 

 for the summer (June-August), the spring and 

 fall (April-May and September-October), and 

 the winter (November-March) for Vessel A and 

 Vessel B during 1952-53, years combined. The 

 skipjack tuna catch per month and per hour of 

 scouting and fishing, and per pound of live bait 

 used shows a decided seasonal trend. Catches 

 were highest in summer and lowest in winter. 

 The trend is less obvious for baiting, except 

 for a peak in the night baiting returns during 

 the spring and fall. The data for bait catches 

 during daylight indicate a reversal in the sea- 

 sonal trend for Vessel B as compared with 

 Vessel A. Night baiting was highly productive 

 in spring and fall; catches in these periods 

 averaged 71 percent of the total catch of bait 

 at night for Vessel A and Vessel B. The data 

 for the two vessels were pooled for 1953, but 

 the night-baiting record for Vessel B was ob- 

 viously incomplete for 1952 and was not 

 included. 



The rate of encounter between fishing ves- 

 sels and fish schools varied with the season. 

 Although the number of schools sighted is not 

 routinely logged by the commercial fishing 

 fleet, data collected on research vessel cruises 

 show that fewer schools are seen in winter 

 than in other seasons (Royce and Otsu, 1955). 



Size composition of the skipjack tuna catch 

 also varies seasonally. Schools of "season" 

 fish, in which individuals weigh from 6.8 to 

 11.3 kg., usually migrate into Hawaiian waters 

 during the summer but are largely absent dur- 

 ing other seasons. The abundance of large fish 

 in the summer fishery explains in part the ap- 

 parent seasonal change in the skipjack tuna 

 catch per unit quantity of live bait used in fish- 

 ing. Although small tuna can be hooked and 

 landed more rapidly than large ones, the weight 

 of the landings probably increases with the size 

 of fish landed, but not in direct proportion. 

 Since extremely large fish must be gaffed, the 

 weight landed per unit time declines. 



The size of the fish caught, therefore, is an 

 important factor affecting the catch of skipjack 

 tuna per unit quantity of bait used; size is not, 

 however, the only source of variability in this 

 index. The quantity of live bait available is the 

 amount caught by the fishermen less the amount 

 of subsequent mortalities in the baitwells; the 

 bait used for fishing can be overestimated if 

 losses of bait are high. Variations in the size 

 of vessel crews also affect the efficiency of 



