Schaefer (1967) used as a measure of fishing 

 effort the average number of boats during the 

 period, adjusted for changes in the size composi- 

 tion of the fleet. In 1970, Schaefer, recognizing 

 that this measure could generate some bias, 

 utilized as a measure of fishing effort the number 

 of trips made by the fleet, times the average 

 vessel capacity (ton-trips). This unit was also 

 utilized by Boerema et al. (1965). However, all 

 these studies ignored the effect of technological 

 change and increased fisherman skills on the 

 level of landings. This neglect arose from the 

 difficulty in quantifying these variables. 

 Although for several advanced fisheries these 

 two variables can indeed be ignored, such 

 neglect is questionable in the Peruvian anchoveta 

 fishery. The importance of such variables was 

 recognized by Gulland (1968). 



The size of the Peruvian fleet has increased 

 from 462 units in 1959 to 1,064 in 1962 and to 

 1,836 in 1964. After 1964, fleet size began to 

 decline, reaching 1,308 units in 1969. From 

 these figures it is clear that up to 1964 a large 

 percentage of the skippers and fishermen were 

 fishing for the first time. However, after 1964, 

 with the reduction of the fleet size, only the 

 most efficient skippers remained in the fishery. 

 This situation and the experience gained by the 

 fishermen after several years of operations, have 

 sei-ved to increase the average skill of the 

 fisherman. 



In addition to increased labor skills, during 

 the last decade several technological innovations, 

 such as power block, echo sounder, steel vessels, 

 and pumps for transferring the fish from the 

 net to the hold, have been gradually introduced 

 into the fleet. In 1969, 92% of the fleet had at 

 least three of these items of gear, as opposed 

 to 79% two years before. If a measure of fishing 

 effort omits the effect of increased labor efficiency 

 and technological innovations, then the most 

 recent estimates of fishing effort will be biased. 

 The estimation of the optimal fishing effort 

 will also be biased. 



The type of bias that will be introduced by 

 omitting the increased efficiency of the fleet can 

 be deduced from Figure 1. 



In Figure 1, if the efficiency of the fleet 

 increased during periods 1 to 3, the observed 

 data for catch and effort will produce curve A. 

 However, the relationship of catch to effort in 

 terms of efficiency in year base "0" is given by 



curve B. The effect of ignoring increased ef- 

 ficiency would be to underestimate the most 

 recent measures of fishing effort. If the observa- 

 tions of fishing effort, unadjusted by efficiency, 

 are consistent from year to year, they still will 

 give a correct measure of the maximum sus- 

 tainable yield, as it is shown in Figure 1. 

 However, the determination of the optimal level 

 of fishing effort, in terms of some constant level 

 of efficiency, will be biased. Usually, one is 

 interested in obtaining the optimal level of 

 fishing effort in terms of efficiency during the 

 current period. This relationship is given in 

 Figure 2, where "period 3" is the current period. 



Since vessels are more efficient during period 

 3, to obtain the maximum sustainable yield 

 C2, the industry will require a smaller effort 

 in terms of number of ton-trips than the effort 

 used in period 2. In fact, instead of requiring 

 an effort Ei, the industry will require only an 

 effort E'2, considering the higher efficiency of 

 vessels in period 3. It is obvious that to obtain 

 an unbiased optimal level of fishing effort at 

 current efficiency, it will be necessary to adjust 

 the index for fishing effort to reflect technological 

 change, changes in fishermen skills, and other 

 variables. 



Although the construction of an index for 

 fishing effort that includes technological change 

 and other such variables is the ideal method to 

 determine an unbiased level of optimal fishing 

 effort, usually it is not easy to construct such 

 an index. This is because several of the above- 

 mentioned variables are difficult to quantify. 

 When this is the case, an alternative approach 

 has to be devised. 



The alternative approach that is used in this 

 paper is to adjust the level of landings obtained, 

 rather than the level of fishing effort, for changes 

 in efficiency. That is, given the observed un- 

 adjusted fishing efforts and the landings in 

 several periods, the problem is to obtain a catch- 

 to-effort relationship that will show that level 

 of landings that would have been obtained in 

 the several periods if vessels of efficiency of the 

 current period would have been used. This 

 adjusted curve and the actual observed curve 

 are shown in Figure 3. The optimal level of 

 fishing effort in terms of vessels of current 

 efficiency {E*-i in the figure) will be obtained by 

 maximizing catch in curve A. 



The difference between this approach and the 



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