196 ANIMAL LIFE AND HUMAN PKOGEESS 



adults ; nor is it practicable to devise the control experiment 

 of both adding to and not adding to the same fishery, or two 

 exactly similar fisheries, simultaneously, so as to secure 

 comparable results. But it may be pointed out that much 

 help may have been given to a depleted fishery although no 

 effect is noticeable. The condition of the fishery might have 

 been worse had no artificial help been given. 



When one thinks of the enormous numbers of eggs pro- 

 duced naturally, in a season, by most of our common fish, as 

 shown in the following list, one is inclined to fear that the 

 comparatively small number of millions, or even of hundreds 

 and thousands of millions, of young fish turned out from 

 hatcheries will be of little avail, and may amount to nothing 

 more than the proverbial " drop in the bucket." 



The average number of eggs spawned by a single female 

 fish in the course of one season is : — 



But probably a truer conception of the state of affairs is 

 obtained by reflecting that while countless millions are pro- 

 duced, countless millions also perish each season from natural 

 causes (as opposed to man's operations) — that is, from their 

 natural enemies and other adverse influences in the environ- 

 ment. As eggs, as embryos, as larvae and as post-larval 

 young fishes, they are the food of most of the larger animals 

 around them in the sea. Probably only a very few out of 

 each milUon reach maturity, and it is out of that scanty rem- 

 nant that the fisherman takes his toll and so may in some 

 cases " over-fish " a Hmited area so as to reduce the population 

 below its power of recovery. The enormous numbers pro- 

 duced do not, then, necessarily mean an enormous rate of 

 increase, but they may afford man his opportunity to step in, 



