It is noteworthy that, 

 although in the post-war years 

 the fishing intensity and the 

 total catch rose substantially, 

 the apparent abundance has re- 

 mained, on the average, as high 

 as in the early days of the 

 fishery. From this it may be 

 concluded that the skipjack are 

 being very much underfished, 

 since the effects of increased 

 fishing intensity on the stock, 

 if any, are so small that they 

 cannot be detected against the 

 background variations. It 

 would appear, therefore, that 

 it is biologically possible to 

 obtain a much greater yield 

 from the Eastern Tropical Pa- 

 cific than is presently being 

 obtained. Since the effect of 

 fishing on the stock is, so 

 far, not capable of measure- 

 ment, we cannot determine the 

 level of maximum yield, but we 

 may be quite confident that it 

 is very much greater than the 

 present harvest. 



For the yellowfin the 

 situation is rather different. 

 It may be seen from figure 5 

 (page 1|0) that changes in abun- 



Table 2. --Number of California tuna purse-seiners 

 by size category, based on capacity 

 tonnage, 1931-58. 



CATCM-TOTAL EASTERN pacific 

 CATCH PEA OAT'S FlSHIHO- CLIPPERS 

 STANDARDIZED TO CLASS 3 



dance over the series of years 193i*-57, 

 bear a measurable relationship to changes 

 in intensity of fishing and harvest. It 

 may be noted that as the intensity of fish- • 

 ing increased prior to World War II, there 

 was a corresponding decline in the catch- 

 per-day's fishing, although the total land- 

 ings continued to rise. With the decrease 

 of intensity of fishing during the war, the 

 harvest decreased, but the catch-per-day's 

 fishing recovered substantially. With the 

 rapid increase in fishing intensity in 

 post-war years, there was a corresponding 

 rapid increase in catch, but a fairly steady 

 decline in catch-per-day's fishing. Follow- 

 ing about 1951, the fishing intensity has 

 tended to fluctuate with corresponding 

 inverse fluctuation in the apparent abun- 

 dance, and with related variations in total 

 catch. 



Figure 4. — Catch, catch-per-day's fishing, 

 and fishing intensity, skipjack tuna, 

 1934-57. 



It is possible from these data of the 

 yellowfin fishery to arrive at an estimate 

 of the average relationship between fishing 



39 



