CONSERVATION OF THE HALIBUT — THOMPSON 



373 



between these derived curves of yield and abundance and those 

 actually obtained from our records was clear evidence of the correct- 

 ness of the theoretical basis of the calculations (figs. 1, 2). 



As an additional proof, regulation reducing the intensity of the 

 fishery over a period of 4 years has given the results that would be 

 expected. With the limit in pounds for each area unchanged, the 

 amount of fishing has been greatly reduced and the abundance on 

 the banks increased, in the case of the southern banks about 60 

 percent. In the present condition of the fishery it therefore seems 

 reasonable to conclude that the abundance on the bank and the 



NUMBER OF SKATES 



CATCH PER SKATE 



^— — TOTAL LANDINGS ' 



ACTUAL 



J925 1927 1929 1931 1933 13 5 19 



FiGORB 1. — Comparison between actual halibut yield and yield expected on a basis of 

 theory, showing the total yield and the yield per unit for the grounds south of Cape 

 Spencer, Alaska, 1925-33. A sljate is a unit of gear, set once. 



number of spawners can be increased at the expense of a reduction 

 in the amount of fishing, very likely without loss of poundage, or 

 even with a gain, until finally new supplies of young allow an 

 increase. 



In this consideration of the effect of the fishery upon the species, 

 a very important economic fact has not been stressed. Throughout 

 the history of the halibut fishery the intensification of the fishery 

 has led to a reduction in the yield per unit. Where the total yield 

 tended to be the same for the more and the less intense fisheries it 

 can readily be seen why the yield per unit varied in reverse fashion 

 to the number of units set. Even where the total yield was thought 

 to have increased, this was not sufficient to obscure the decrease in 



