FISHERY BULLETIN: VOL. 74, NO. 1 



Table 4. — Estimating the number of days fished among class 1 vessels fishing in the 



inshore area, January-December 1948. 



1948-64. For example, Table 4 shows the data 

 used in the computations and the results obtained 

 among class 1 vessels fishing the inshore area in 

 1948. CIET was derived from the equation, 



CIET (col. 3) 



Monthly catch (col. 1) 

 Number of effective trips (col. 2) 



and converted to logarithms (col. 4). Log CIDF 

 (col. 5) was derived from the equation, 



log CIDF = log a + 6 log CIET 



and converted to CIDF (col. 6). Days fished were 

 estimated from the equation. 



Days fished (col. 7) = 



Monthly catch (col. 1) 

 CIDF (col. 6) 



Standardization of Catch Per Day Fished 



A method of standardizing effort of different 

 size classes of vessel has been discussed by 

 Shimada and Schaefer (1956) for the eastern 

 Pacific yellowfin and skipjack tuna fishery. I used 

 a similar method to estimate relative fishing 

 power of class 1 vessels in the Hawaiian fishery so 

 that their unit of effort was comparable to that of 

 class 2 vessels, which were selected as the stan- 

 dard size class (Uchida 1966, 1967). Briefly, the 

 method involves the use of correction or efficiency 

 factors that are calculated from CIDF of the ves- 

 sel size classes. Efficiency factors adjust the 

 fishing effort of one size class to that of a standard 

 class. For example, under conditions of equal 

 abundance, the class 1 vessels can be expected to 

 produce a smaller catch than the class 2 vessels. 

 From the catches of the two classes, the fishing 

 power of class 1 vessels can be determined rela- 



tive to class 2, the standard class, for a given 

 fishing area. 



To illustrate the calculation of efficiency factors 

 and the standard unit of effort, the annual CIDF 

 given in Table 5 by vessel size classes and areas 

 were used. In 1948, the efficiency factor for class 1 

 vessels fishing inshore was 1.33/1.78 = 0.747 and 

 for offshore was 2.07/3.46 = 0.598. The efficiency 

 factors for class 2 vessels were fixed at 1.000 for 

 all years. The mean efficiency factor, 0.668, is the 

 geometric mean of the inshore and offshore val- 

 ues. The geometric mean is appropriate for av- 

 eraging ratios. 



Varying from 0.59 to 0.82 (rounded) and av- 

 eraging 0.71 in 1948-70, the efficiency factors 

 demonstrated not only the greater capability of 

 class 2 vessels, but also the wide variability of the 

 factors from year to year. There was no evidence 

 that the efficiency of class 1 vessels increased or 

 decreased relative to class 2 vessels. Therefore, 

 neither the efficiency of the standard class nor 

 that of class 1 vessels has been altered by the loss 

 of the less efficient or marginal vessels. 



MEASURES OF APPARENT 



ABUNDANCE 

 AND FISHING INTENSITY 



Estimate of the apparent abundance of skipjack 

 tuna on the fishing grounds, expressed as catch 

 per standard day fished (CISDF), can be calcu- 

 lated from efficiency factors and the total number 

 of days fished for each of the two classes of ves- 

 sels. For example, in 1948 there were an esti- 

 mated 1,444 fishing days among class 1 vessels 

 and 829 days among class 2 vessels. The standard 

 days fished is the sum of the products of the mean 

 efficiency factor and the total number of fishing 

 days of the size classes. CISDF is found by, 



66 



