pounds. Thus, if we harvest them all at the start of the year, 

 our yield would be 5000 pounds. Suppose that we let the fish 

 remain for the year, that none of them dies from naturcd 

 causes during the year, and that each fish gains one pound 

 in weight. At the end of the year, the available catch is 6000 

 pounds. Therefore, catching the fish at the end of the year 

 rather than at the start, our yield increased by 1000 povmds, 

 because the gain in weight exceeded the loss due to natural 

 mortality. 



On the other hand, suppose that during the year we let 

 the fish remain, 500 of them died from natural causes, 

 leaving only 500 for harvesting at the end of the year. The 

 yield at the end of the year would be 500 times 6 pounds, or 

 3000 pounds. The yield would be ZOOO pounds less than it 

 would have been had we harvested at the start of the year, 

 because the loss due to natural mortality exceeded the gain 

 in weight by the survivors. Similar knowledge of the growth 

 and natural mortality of halibut and herring enable us to 

 estimate when and how much fishing shovild be employed to 

 obtain the ma:ximum yield from a given number of fish 

 entering the fishery. If the current fishing intensity is lower 

 than that which provides the estimated maximum yield, we 

 wovild conclude that an increase in fishing would provide an 

 increase in yield. If the current fishing intensity is at or 

 above that which provides the estimated maximum yield, 

 we would conclude that more intensive fishing would not 

 provide an increase in yield. 



Another type of evidence can be used to study the quali- 

 fication of a stock for abstention. It consists of the historiced 

 changes or trends in catch, fishing effort and relative abun- 

 dance of a stock. The conclusions to be drawn from this type 

 of evidence are usually rather general. Nevertheless, they 

 are, if logically, drawn, based on the same biological prin- 

 ciples and concepts as those drawn from the more rigorous 

 analytical treatment of return-escapement data orgrowthand 

 natural mortality data. 



With regard to the second condition for abstention, it is 

 necessary to demonstrate that our reg\ilatory measures are 

 designed for the purpose of achieving maximum sustained 

 yield, and that they are based on the findings of scientific 

 research. 



For the third condition for abstention, it is necessary to 

 explain the scope and objectives of our research programs. 

 It should be emphasized that, unless the third condition for 

 abstention has been and is reasonably satisfied, we lack the 

 scientific evidence required to study the qualification of a 

 stock under the first condition for abstention and to serve 

 as a basis for regulatory measures. Clearly, the three con- 

 ditions for abstention are closely related. 



During the past three years, we have assembled various 

 types of scientific data concerning utilization of our stocks 

 and other information relating to regulation of and research 

 studies on the stocks. These data and information represent 

 a body of knowledge on our salmon, halibut and herring 



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