316 BRITISH FISHERIES 



the time of the absorption of the yolk-sac, and further 

 during the metamorphosis. In the hatchery we 

 seek to avoid this mortality by providing the larvae 

 with suitable food. 



In an " over-fished " area, we assume that there 

 are fewer mature fish this year than last (or this 

 year than formerly) . Therefore fewer fry reach the 

 nurseries. This loss of fry must be compensated. 

 If we take a number of spawning fish from the 

 sea and let them breed in the hatchery, and take 

 all imaginable care of the resulting larvae, and 

 then turn out the parent fish and the larvae under 

 the theoretically correct conditions, there is a 

 distinct gain. We have saved the larvae which 

 would have been destroyed in nature. Now, this 

 gain in the number of larvae must be equal to that 

 number of larvae which would have been produced 

 (and attained the nursery grounds) by the excess 

 of fish caught this year over those caught last 

 year (or formerly). In this way we compensate, 

 by artificial culture, for over-fishing. 



This is the rationale of sea-fish culture. Is the 

 above argument sound ? Apparently it would be, 

 if the premises were sound. But, on examining 

 the latter, it is not certain that this is the case. 



i. We do not know, even approximately, what 

 proportion of the eggs and fry produced naturally 

 are lost through the physical causes mentioned. 

 We suspect, with reason, that great loss occurs, but 

 we do not know to what extent this takes place. 



