PROGRESS IN BIOLOGICAL INQUIRIES, 1926 583 
will link these three graphs—of intensity, abundance, and yield—lies the 
problem of fisheries science as I see it. 
It seems to me, from my experience with the halibut and my reading in 
fisheries reports, that it is possible to maintain the abundance at a higher level 
by restricting the fishery. Thus, the yield per skate on our Pacific coast is 
directly correlated with the cost of operations. Banks as far away as Kodiak 
Island yield now about 120 pounds per skate; near Cape Ommaney about 
60; and in Hecate Straits 48. Of course, these areas may be on a continuous 
decline, but the rate of the decline is determined largely by economic condi- 
tions, and possibly it might be stopped easily. The question then arises, what 
might the yield be were the decline stopped at any particular level? Would 
it be noticeably less at the higher levels of abundance? It might be greater. 
We must at once admit that there may be a remote possibility that a fixed 
level of abundance (say at 40 pounds to a skate) would remain at that level 
even though 40,000,000 pounds were taken out by a highly intensified fishery 
of 1,000,000 skates yearly; whereas a fixed level at 120 pounds to a skate 
might yield, without decline, about 20,000,000 as the result of the use of but 
one-sixth of a million skates. The difference in total yield of 20,000,000 might, 
sore |e | 

/907 1909 ‘9 a Ke 1917 19/19 /9el (923 1925 
Fic. 13.—Hypothetical abundance in halibut fishery, showing various levels (left mar- 
gin and unbroken line) and the numbers of skates required (right margin and 
broken line) to produce a fixed annual yield of 100,000 pounds 
from an economic standpoint, justify the principal of making the public pay 
all it could. Would it be economically worth while to double the yield by 
fishing six times aS much gear? Perhaps so; perhaps not. 


Case 1 | Case 2 

: . Hat | 
PANSUITIGBN CG 3a noe ae ae | 40 pounds per skate. --.--.._-.=-..___- 120 pounds per skate. 
BLO ViClO as en oe! See ek 1240'000;000 DOURUSs-- - 2225-22 S22 ee 20,000,000 pounds. 
Priterisit yes. Sees Ss. ees leas O00! 000!skaties ees avai ssc See 166,667 skates. 
| 2 2a i z 

However, we have no such knowledge as to the course of events. The total 
yield might very well be the same in both cases, or even greater under restric- 
tion. Nor do we know what the final reaction of a species is to intensified 
fishing. That is a biological problem of first magnitude to which we will 
return. 
As we have said, the great fisheries have been and are in a condition of 
constant increase of efficiency and intensity. This increase has been so con- 
sistent and continuous as to give ground for thought as to whether it will 
reach a limit, or as to what a terrific strain it may finally impose on our 
available species. 
The total yield, however, has not increased correspondingly in the threatened 
fisheries, such as plaice and halibut, however much it may have in those 
