species, mortalities due to catching, handling, 

 and transfer to the vessels' baitwells must be 

 minimized. Baitfish mortality was one of the 

 important reasons for the rejection by the fish- 

 ermen of an independent bait fishery in the past. 



Hatchery rearing of a suitable baitfish has 

 some attractive features, if it can be done eco- 

 nomically, since the supply of bait could be 

 regulated to the needs of the fleet. The vessels 

 could depend less on the availability of bait on 

 the baiting ground. 



Certain apparent characteristics of the nehu 

 strongly influence the operations of the skipjack 

 tuna fishery. They include a low average rate 

 of capture--about 11.3 kg. per hour during the 

 summer season--and a high mortality there- 

 after. Baitfish mortality usually averaged 

 about 25 percent a day after capture. Brock 

 and Takata (1955) found an hourly average in- 

 stantaneous mortality of 0.013 for nehu taken 

 by lift net at night and held thereafter in run- 

 ning sea water for 36 hours. This estimate of 

 mortality agrees approximately with the 25- 

 percent estimate, if the latter is considered as 

 applicable to the initial 24 hours after capture. 

 Day baiting, however, requires additional hand- 

 ling of the baitfish in comparison with bait 

 fishing at night with a lift net; therefore, it is 

 likely that the average day-bait mortality for 

 the initial 24 hours following capture is greater 

 than 25 percent. Although no data are available 

 on mortality for longer periods, the limited 

 length of time that a catch of baitfish can be 

 used for fishing suggests that the baitfish 

 mortality does not decline greatly after the 

 initial mortality following capture (table 4 and 



fig. 1). 



The rate of capture of bait during daylight 

 must be sufficiently high to provide enough bait 

 for a day's fishing. Bait caught at a rate of 

 11.3 kg. per hour would in 1 day, on the aver- 

 age, provide an adequate supply for a day's 

 tuna fishing. At this rate of capture, however, 

 a vessel could have difficulty in accumulating 

 enough bait if it preferred to fish at least a 

 week. The problem of accumulating bait is 

 further compounded by the high mortality; an 

 hourly instantaneous rate of 0.013 is about 

 equal to a weekly mortality rate of 0.889 or 

 nearly 90 percent. The size of the baitwells, 

 the tuna-carrying capacity, icing requirement, 

 and useful cruising range of the vessels, there- 

 fore, are limited by the average rates of cap- 

 ture and mortality of baitfish. These charac- 

 teristics of the vessels are responsible for the 



fishing pattern of a day or two of baiting fol- 

 lowed by 1 to 5, but usually 1 or 2 days of fish- 

 ing. Numerous short episodes of baiting and 

 fishing increase the time spent traveling be- 

 tween baiting and fishing grounds, and make the 

 development of a long-range fishery elsewhere 

 in the central Pacific an impossibility if pres- 

 ent practices in the use of this baitfish species 

 are continued. A long-range fishery during the 

 winter, however, may be the best means of in- 

 creasing the production of skipjack tuna during 

 the off-season months. Under present condi- 

 tions, an "improved" vessel design for the 

 fishery is difficult to visualize; the present 

 vessels may represent nearly the optimum 

 considering the low rate of capture and surviv- 

 al of the nehu. 



The duration of the fishing trip was inde- 

 pendent of the duration of the baiting period, 

 which was not surprising. The time spent in 

 the capture of bait showed a significant nega- 

 tive correlation with the time available for 

 fishing (r = -0.551) but showed no correlation 

 with the actual time spent fishing. The quantity 

 of bait taken to sea, however, was positively 

 correlated with the duration of the fishing trip 

 (r = 0.395), but not significantly so with the 

 skipjack tuna catch. Furthermore, the corre- 

 lation between the time spent fishing per trip 

 and the catch was not significant. Perhaps it 

 should be pointed out that the significant corre- 

 lations shown above do not account for a great 

 deal of the above variation. These results 

 suggest that baiting proceeds until an adequate 

 supply of live bait is aboard, after which fish- 

 ing proceeds until a load of fish is obtained or 

 the bait supply is exhausted. If fishing is poor 

 but a large quantity of bait is aboard, the 

 period spent fishing will, on the average, be 

 longer. If fishing is good, the bait supply will 

 be used more rapidly, but because of high bait- 

 fish mortality, the resulting catch will not 

 necessarily be large (except occasionally with- 

 in a 2-day period following baiting) even though 

 the preceding bait catch was large. 



Availability of Vessels 



The availability of the vessel for fishing is 

 affected by maintenance and repair, traveling 

 time between port and baiting grounds, delivery 

 of fish or picking up ice, and time spent ashore 

 for a wide variety of reasons. The "active'' 

 time, which included that spent in traveling, 

 bait fishing, and scouting and fishing, for the 



