582 U. S. BUREAU OF FISHERIES 
stantly increasing intensity necessary to maintain the yield. With regard to 
other species, what reason have we to rely upon the belief that the most 
prolific and as yet untouched species will not follow in the path of the halibut 
and the plaice, in the face of the infinite threat of mankind’s expanding powers? 
I will use the halibut to illustrate my theme, as I am most familiar with it. 
The details of the decline in catch per skate of 210 hooks have not been worked 
out fully, but in so far as they have, the curve of abundance may be shown 
tentatively in Figure 12, where the decline is represented on a logarithmic 
scale to show that it is taking place at a steady rate of fall. The straight line, 
representing the rate of fall, is translated in Figure 13 into actual poundage per 
skate of 210 hooks to give a hypothetical curve of abundance. 
In any subsequent remarks concerning abundance you will understand that 
by abundance I mean this yield per skate of 210 hooks. This is the most 
accurate measure of abundance we find at hand. ~ 
This decline represents only the older section of the banks, which constitutes 
now a more or less distinct fishery. The total yield from this has declined 
greatly in recent years; just how fast we do not yet know, but we may draw 
in a level line in Figure 138, representing the total yield as shown, for the pur- 
poses of discussion. Nor do we as yet know the intensity of the fishery from 
year to year, but we may calculate, from the yield per skate, what it must be 
to maintain the total yield, and we represent its increase by a tentative line, 
rising rapidly. In general our work supports these curves, as they would be 
modified by a declining yield. 
LOGARITHM OF AVERAGE CATCHES PER SiG 
~ 
nD 

eee 
1906 + +(98 190 192 1/94 1916 19/8 ~~ ~*(1920 1922 1924 

Fic. 12.—Rate of decline of halibut catch per unit of gear, represented on a logarith- 
mic scale to show the steady rate of fall. Short straight line shows rate of fall as 
determined from data for 1906 to 1914, inclusive. Long straight line shows rate of 
fall as determined after addition of data for 1925. 
1 woutd call your attention to a fact that all the trade knows—that the 
economic effort involved for the yield obtained has steadily risen, just as is 
shown by the increased number of skates in Figure 13. It would seem to me 
that in this is to be found one of the worst phases of the dreaded overfishing. 
The lattcr might be defined as that condition of a fishery in which the cost of 
operation is a maximum for the yield obtained. Let us, for the time being, 
forget the fears for the very existence of the fishery and think only of this 
economic condition. The cost of operation of this fishery is raised auto- 
matically to the highest point the traffic will bear. It is, in very fact, making 
the public pay as dearly as it possibly can for what it gets. A very slight 
change in prices or costs would be disastrous. That may be overfishing. Every 
improvement in gear, in engines, or in vessels enables the intensity to rise, as 
I have seen myself, repeatedly, in the halibut fishery in such cases as the 
adoption of small hooks. And it must automatically result in decreased 
abundance, as shown by yield per standard hook. The reopening of the war- 
closed North Sea automatically resulted, by this reasoning, in a resumption of 
the preceding level of abundance as determined by economic factors, not neces- 
sarily by biological factors. It does not seem to me necessary to seek a 
biological explanation for this seemingly more stable lower level. 
I have made this statement most emphatic for the purpose of clarity. In 
reality, we do not know enough about the relationship of these curves to 
discuss them intelligently. There are statistical, biological, and economic 
phases to this great problem, but in that equation, or series of equations, which 
