INTERNATIONAL FISHERIES COMMISSION 11 



and the various species of birds introduced into America to trans- 

 planted species of fish, such as the shad and various insect pests. 

 Among indigenous species this phenomenon must hold true in order 

 that they may recover from disastrous years. Whether this is caused 

 by a greater abundance of food for the fewer individuals or by 

 some other factor, it would seem to be a general rule that the rate 

 of replacement is higher when the species is below its maximum in 

 numbers. Hence, if the decline has not gone too far it is to be ex- 

 pected that in response to steadiness of the mortality rate the num- 

 bers of the species will decline only until the thereby increased 

 rate of replacement is sufficient to balance the mortality. 



With the data at liand. evidence of this increased productivity 

 in the halibut is available. The abundance has fallen on the grounds 

 south of Cape Ommaney in IG years to about 25 per cent of its 

 original amount, but the total catch seems to have fallen to about 

 40 per cent, therefore not as fast. Such a calculation can not, in 

 the nature of things, be exact; yet it errs on the conservative side, 

 as for reasons that can not be detailed here, the fall in abundance 

 may have been greater than this, possibly to such a degree that the 

 present abundance is but 15 per cent of its original amount. In this 

 case the contrast with tlie decrease in total catch is still more marked. 

 Tlie lower level of abundance seems to have produced in recent 

 years a higher catch in proportion, although not in total figures. 



There is. therefore, ground for believing that if the proportion 

 taken does not increase, the halibut fishery on the older banks 

 will ultimately come to a position of stability. This would im[)ly 

 the reduction of the total catch at a rate equal to the fall in abund- 

 ance of the stock of fish. The latter can best be measured by the 

 returns per set of a standard unit of gear. This indicates that from 

 1906 to 1920 the fall has been at the rate of 10 per cent a year. 

 Such a reduction in total catch is the miniinum that could be con- 

 sidered for the purpose and is equivalent to the use of a fieet and 

 gear the equal of that now employed. 



It will be noted that the essential princi]ile of the reduction in 

 total catch is that it shall jiroceed at a rate at least eciual to that of 

 the decbniug return from a definite Jimount of fishing. Were this to 

 be accomplished with precision, the nMluction in catch would cease 

 iimnediateh' with the cessation of the decline in abundance; and with 

 a definite amount of fishing the returns woidd tiien be constant. It 

 is the same principle u])on which regulation of the salmon fisheries 

 in Alaska and liritish Columbia is conducted — that a definite pro- 

 jxjrtion of the fisli shall be allowed to ])ass the commercial fisherman. 



Tlie adoption of such a procedui'e must be made with full knowl- 

 edge that it may not suffice. The thinning out of the i)o|)ulation may 

 have already gone so far as to have increased the rate of replacement 

 to its maxiiniim. No further increase may be ])OSsible, so that the 

 present degree of intensit}' of fishing may suffice to continue the 

 decline, or the present drain on the species may exceed anything that 

 even an increased rate of replacement may be able to care for. In 

 such ca.se the only alternative would be to reduce the catch annually 

 at a faster rate. That is for the future to indicate. 



On the other hand, it is well recognized by the fishermen that the 

 iiiinks are now but a cry sparsely populated, and it is more than pos- 



