372 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



If, for the sake of brevity of treatment, we suppose the fishermen 

 to take the fish at a high rate, 90 percent annually, the poundage 

 of the stock surviving each year would be as in column 1 of table 2. 

 But at the time this class was 5 years old the next older age class 

 would have been reduced to 400, as shown in column 2, the next 

 older to 40, etc. And there would be 4-year classes present on the 

 banks, totaling 4,444 pounds. 



If, however, the fishery were less intense, say 80 percent annually 

 instead of 90 percent, the same calculation will show that the tak- 

 ing of the 4,000 pounds would be spread over 6 years instead of 4, 

 and that there would then be 6-year classes present on the banks, 

 totaling 5,000 pounds. (See table 3.) 



Yet in both of these cases the fishermen would get 4,000 pounds 

 from each age group, and their catch from all the age groups pres- 

 ent would total 4,000 pounds each year. But the amov/nt of fish left 

 on the hank would be greater under the less intense fishery^ and they 

 would reach a greater age. This would mean that the less intense 

 fishery would catch as much as the more intense, yet would allow 

 more fish to reach spawning size. (Incidentally, in halibut, eggs 

 are produced approximately in proportion to weight. ) 



Of course, had the growth exceeded the loss by death, the fisher- 

 men would actually have gained ^poundage by a less intense fishery, 

 because it would allow a greater growth. Artd, on the other hand, 

 had growth been less than loss by death the fishermen would have 

 lost poundage even though the amount of fish reaching spawning 

 size had been greater. 



These are simplified cases. Under an intense fishery, such as ex- 

 isted in the southern halibut banks, only the younger age groups 

 are present in any numbers. Among such ages growth seemed to 

 equal or even exceed the loss by death, as nearly as our estimates 

 could indicate. Had the fishery been much less intense, and had the 

 fish survived to a much greater age as a consequence, natural deaths 

 would have increased among these older fish and growth would have 

 decreased. Hence, although it was fair to expect that in the depleted 

 fishery a lessened intensity would either not reduce or would in- 

 crease the yield and, would increase the number of fish reaching 

 spawning size, yet this rebuilding of the stock would ultimately 

 produce a condition where natural deaths would outbalance growth 

 and further reduction of intensity would become unprofitable unless 

 the number of spawners was still too small. 



This analysis was tested by theoretical reconstruction of the stock 

 according to the estimated rates of growth and death, and accord- 

 ing to the intensity of the fishery. The latter was determined by 

 the number of units of gear set each year. The close correspondence 



