Had it been possible, to include fishing intensity or its complementp 

 relative abundancej^, today's task would be enormously facilitated« 

 Eren so, it would be necessaty to relate or transform the characterise 

 tics of catch to those of the stock, for replenishment depends on the 

 fish that are left in the seao 



Of course, if the fishery took a random sample of what is in the 

 sea, the characteristics of catch would be the same as those of stocko 

 But if we can b e sure of only one things it is that the fishery does 

 not take a random sampleo In the Pacific Northwest (Oregon^ Washington, 

 and British Columbia) the fishery over=samples the older fish? in so'jithern 

 California, the youngo In Central California, it perhaps over-^samples 

 those of intermediate af;eSo In certain areas between ports, notably 

 off northern California and southern Oregon,, there is no fishingo At 

 a single port, the -size composition changes significantly from d ay to 

 day, week to week, and month to month, and there is no assurance that 

 the catch of the various sizes is proportionell to their relative abundance 

 in the seao In fact, it is obvious that the various components of the 

 stock are represented in the catch in proportion to the length of time 

 each is subject to fishing in a particular area and not at all in pro= 

 portion to its abxindance in the sea© 



Thus the major problem of research is how to deduce the characteris= 

 tics of the stock from the available samples in the catcho Once those 

 are known, total mortality can be estimated by computational processes 

 developed by Bayaa&v, Thompson and Bell, Ricker, and others© Also under 

 certain conditions, it will be possible to separate natural from catch 

 mortality! and both being known, to compute the recruitment (the equiva= 

 lent of the actuary's birth-rate, taken as of the attainment of commercial 

 size) o 



Analysis 



In the diagram, the central part^analysis is taken up with the 

 processes concerned with adjustments, conversions, and combinations in= 

 tended to transform data from the catch into attributes of the stocko 

 These processes leading to *vital statistics* are so compleg that simple 

 appraisals of their reliability by conventional statistical methods are 

 unavailing* Confirmation must, therefore, be sought in results attained 

 through independent approaches » The only other approach that is currently 

 being followed is taggingo The processes involved in this branch of re= 

 search are noted in the left=hand portion of the diagram and will be dis= 

 cussed under the heading of "T&gging researoho* Even after determinations 

 of mortality and recruitment have been made by two methods and one found 

 to varify the other, it is still necessary to investigate recruitment be^ 

 cause changes in it are of differing significance, depending on whether 

 they be due to the changes in the stock itself or to fluctuations in the 

 environment o The fBiaasesable means of dealing with this problem are listed 

 in the right-hand part of the diagrams, and will be discussed under the 

 heading, "Recruitment researcho" 



=^ At uniform availability and with no competition between units of gears 

 Relative abundance = catch=per=unit=of =eff ort.? and 

 number of units of effort = Catch 



Catch-per-unit-of -effort 



