SEA-FISHERIES LABORATORY. 163 



Whether that amount of destruction of small fish is a thing to 

 be restricted or prevented is not so easy a question to answer 

 as it appears to be at first sight. To that again, we return in 

 a later section of this report (see p. 231) 



The Nursery Grounds and their Conditions. 



These extensive shallow-water nursery grounds are of 

 extreme importance to the fisheries, and it may well be the 

 case that the attention of future fishery authorities will be 

 directed to them far more than to the offshore regions, which 

 at present almost monopolise investigation. From the natural 

 history point of view they are of surpassing interest, and we 

 feel that far too little research goes on here. They are by far 

 the most " productive " zone of the sea, and that is, of course, 

 the reason why they are fish nurseries. The conditions that 

 make them productive are : (1) The drainage from the land 

 carrying fresh water which brings down enormous quantities 

 of organic substance, in solution or as a sediment (all of this 

 is utilised by living organisms) ; (2) The low salinity of the 

 water ; (3) The relatively high temperature, and (4) The 

 greater degree of sunlight. The sand everywhere contains 

 abundant vegetable life in the form of Diatoms, Flagellates, 

 and Dinoflagellates (microscopic plants and " plant-animals "), 

 and one can, nearly everywhere, see this as a yellow-brown or 

 greenish scum on the surface of the sand. Beneath the surface 

 the sand is, nearly everywhere, blackish in colour as the result 

 of the action of sulphuretted hydrogen produced by the 

 decomposition of dead organic substance. In the surface layers 

 of the sand and in the water just over that layer there are 

 numerous Copepods and small worms. Nearly everywhere 

 there are very numerous shellfish — cockles, small mussels, 

 Mactra, Scrobicularia, Nucula, etc. A minute fragment of 

 zoophyte may contain dozens of small mussels about the size 

 of a very small pinhead, and on some suitable bottoms the 



