on the bait capacity of most of tiie vessels in 

 the fleet were given by Yamashita (1958; 

 appendix table 1 ) . 



The bait capacity of a vessel is stated in 

 terms of the average eff'ective volume in gal- 

 lons per baitwell and is derived from the length 

 of the baitwell, its width, and its depth up to 

 the water level. 



The size classes of vessels used in this study 

 are as follows: 



Class 1. — Bait capacity up to 800 gallons per 

 baitwell; registered length, 58.3 to 71.9 feet; 

 gross tonnage, 27 to 54 tons; engine, 110 to 

 450 horsepower. Their number ranged from 

 8 to 16 in 1952-62. 



Class 2. — Bait capacity more than 800 gal- 

 lons per baitwell ; registered length, 65.0 to 

 80.5 feet ; gross tonnage, 45 to 77 tons ; engine, 

 160 to 600 horsepower. Their number ranged 

 from 11 to 14 in 1952-62. 



It was necessary to estimate the bait-carry- 

 ing capacity of four vessels for which Yama- 

 shita (1958) gave no records. To determine 

 the most dependable procedure, characteristics 

 such as gross tonnage, net tonnage, registered 

 length, and engine horsepower, were examined 

 in relation to average effective volume of bait- 

 wells. The regression of average effective 

 volume per baitwell (Y) on gross tonnage (X) 

 (fig. 2) proved to have the smallest error of 

 estimate. This relation was used therefore, to 

 estimate the average effective volume of the 

 four vessels. 



THE EFFECTIVE TRIP AS A MEASURE OF EFFORT 

 The records used carried three types of 

 statistics from which one might estimate ef- 

 fort : The number of men hooking per trip, the 

 number of men aboard per trip, and the num- 

 ber of trips. The number of men hooking per 

 trip and the number of men aboard per trip 

 were not consistently entered ; therefore, I 

 selected the number of fishing trips as the 

 unit of eflfort. The catch reports showed all 

 trips on which a catch was made, but gave no 

 indication of zero-catch trips. For this study 

 I define efl'ort as an efl:ective trip (a trip on 

 which skipjack tuna were caught). 



Because zero-catch trips were not recorded, 

 effort always is underestimated. The extent of 



_ 1.600 

 J 1.400 



< 

 o 



J 1.200 



u 



03 



u 

 s 



3 



§ 



800 



400 



10 20 30 40 50 60 70 80 90 



GROSS TONNAGE 



Figure 2. -Regression of average effective volume per 

 baitwell on gross tonnage of Hawaiian skipjack tuna 

 vessels. 



the underestimate may not be serious in some 

 years, because zero-catch trips are fewer when 

 fishing is good (Shippen, 1961). This source 

 of error can weigh heavily, however, in a year 

 of poor fishing, when zero-catch trips become 

 numerous. 



ESTIMATES OF ZERO-CATCH TRIPS 



Because only the number of effective trips 

 is known from the catch reports, estimates of 

 catch per effective trip (Y/g) are larger than 

 if total effort had been used, assuming that 

 zero-catch trips occur from time to time. (The 

 notation Y refers to the total weight of fish in 

 the catch and g to the fishing effort or effective 

 trip as recorded. In a later section of this paper 

 the notation f is used to refer to fishing effort 

 expressed in standard effective trips.) A 

 measure of effort, however, should reflect zero- 

 catch trips as well as those on which fish were 

 caught. 



Logbook records available for a few vessels 

 in 1957-59 provided some data on zero-catch 

 trips (table 3). Five vessels kept logbooks in 

 1957, seven in 1958 and five in 1959 ; the vessels 

 represented 20, 29, and 24 percent of the fleet. 



U.S. FISH AND WILDLIFE SERVICE 



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