as nothing is known as to which of two major influences determine its 

 vaiueo These influences are those i (l) Not connected (let us say^, ex- 

 trinsic influences) J and (2) connected (ioeo, intrinsic influences) 

 with the size of the sardine population itself o The first category would 

 include hydrographic and oceanographic conditions that may influence 

 the amount of spawning and the survival of youngo It would also era-- 

 brace competition with, or predation byj other marine animals o The 

 second category would include the direct influence of population numbers 

 on the amount of spawn produced and the competitive effects of popula- 

 tion numbers on the number surviving. The amount of spawn would be 

 directly, and the amount of survival inversely, proportional to popu= 

 lation numbers „ The survival rates might be different for the various 

 stages of youngo 



So far as intrinsic influences are concernedj, one would expect re = 

 cruitment to be small even at low levels of fishing intensity where there 

 is a very large spawning population and also a very crowded condition 

 which could impose a high mortal! tyo At intermediate levels of fishing 

 intensity there would be maximal recruitment resulting from a still large 

 spawning population and the low mortality associated with an unorowded 

 conditiono At extremely high levels of fishing intensity there should 

 again be low recruitment due to a very small population producing insuf- 

 ficient spawn for maximal recruitment even in a very much thinned-cjit 

 condition where competition within the population would result in neg- 

 ligible mortalityo 



If the intrinsic influences were operating alone,, it would be e 

 simple matter to construct a curve of recruitment according to levels 

 of fishing intensity by merely observing what happens to recruitment 

 over a range of fishing intensities. But the extrinsic influences, 

 operating simultaneously also affect the recruitment o For instance, 

 preliminary analysis of vital statistics for two periods of the sardine 

 fishery showed that quadrupling of fishing intensity was acoompaaiod 

 by doubling of recr-uitmento The earlier period with the low intensity 

 of fishing covered 8 seasons^ and the later one of high intensity, 4o 

 Both periods were thus of sufficient duration to have had a variety of 

 extrinsic influences and their effects on mean recruitment should to some 

 extent ''average out," Yet one would be bold to conclude that they had 

 indeed averaged out and that the increase in recruitment was in fact 

 due to the increased intensity of fishing. On the contrary, one could 

 almost as easily argue that through the later period^, there had been 

 4 years of favorable extrinsic conditions that were responsible for 

 the increase. 



Yet a choice must be made between the alternatives. If the increased 

 recruitment were in fact due to the thinning oxit of the population by 

 intensive fishings then this high rate of utilization^ with the attendant 

 large annual catches could go on with no ill conseouences other than a 

 not intolerable reduction in average size of fish. But if it were due 

 to a lucky run of good survival years^ the present rate of fishing could 



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