96 THE COD 



proved to consist of the floating spores of vegetable diatoms, 

 which form the food of copepods and of some species of fish 

 larvae, in such numbers that it looked almost as though they 

 had been projected over the surface by an explosion. The 

 appearance of these diatoms is not at all constant. It must, as 

 it seems to the writer, resemble the formation of diatomic 



* scum ' on chalk stream springs on sunny days in Great 

 Britain — that hete noire of trout breeders. It is obvious that 

 cod eggs may hatch out, and the mouths of the larvae may 

 begin to function at a time when there are few or none of these 

 diatoms or of the small animals which consume diatoms at the 

 surface within their reach. If that is the case they will be 

 thrown back entirely on the contents of their yolk-sacs for their 



* baby food '. They will be ' weaned too suddenly ', and a large 

 proportion will die — ^just as we have seen turbot may die — from 

 the effect of a sudden change of diet. And on the whole the 

 odds are heavy that this is what will happen in a normal year. 

 On the other hand, there is a chance that the larvae may begin 

 to make their first feeble attempts at feeding just as the mass 

 of little plants comes to the surface in their midst. They will 

 then, like the turbots in Anthony's glass barrels, find the exact 

 food which is necessary to eke out the supply in their yolk-sacs, 

 and an unusually large proportion will survive the ' critical 

 period ', which, in the case of most fish, is probably the period 

 when the sac is just or nearly absorbed. 



Dr. Hjort believes (and every one who has reared thousands 

 of young trout through this ' critical period ', and lost tens of 

 thousands before he learnt the secret, will find it easy to accept 

 the behef) that in 1904 and in 1912 this is just what happened. 

 In both years a big ' rise ' of diatoms happened to occur just 

 as the yoang cod first began to take food. The result was that 

 an abnormally small proportion was wiped out of existence. 

 Now if Hjort's hypothesis is correct it will be seen at once that 

 we are within reasonable distance of being able to forecast the 

 Norwegian cod harvest in any particular water many years 

 ahead. 



So far as cod are concerned — and herrings and haddock also— 

 a series of laboratory experiments on the lines of Dr. Anthony's ^ 

 experiments with turbot and with the same apparatus might 

 settle the question once and for all. Are any such experiments 

 contemplated in this country ? None have been announced. 

 But we may rest assured that they will be made in Norway. 



It is, however, lamentable — almost tragic — that this great 

 work of Dr. Hjort and Dr. Damas should have for years remained 



1 See p. fi7. 



