NATURE ADIUFT 



These places usually contain a wealth of seaweeds and other attached algae 

 and it is rather these than the plankton which seem to get the most benefit. 

 The absorbed fertilizer is so slowly liberated from the muds that it is tem- 

 porarily lost; although it would eventually be liberated it would take a long 

 time. It is thus difficult to assess the actual amount used by the plankton, but 

 it is a relatively small proportion and it is this that will benefit the fish most. 



Further, such confined places rarely form a suitable habitat for the type 

 of fish we would want to grow for economic purposes even though there 

 are plenty of gobies and other shore fishes that can live there. We w^ould thus 

 have to 'weed' the area of unwanted fish and replace them by transplanted 

 hsh or tish bred in hatcheries. All of this is expensive, and only of doubtful 

 value because the confined conditions would not be ideal and the fish would 

 do their best to migrate out of the area. This is an important factor in marine 

 fish which did not need to be taken into account in the fresh-water fish farms. 

 Economically, it docs not look too hopeful, as with the cost of fertilizer, 

 labour, hatching or transplantation it w^ould probably cost more to rear 

 each fish than its market value. 



If, instead, we consider an open bay some of these disadvantages disappear; 

 the seaweeds are not a major item, the bay is an acceptable natural environ- 

 ment and would be naturally re-stocked. If we choose one where the tides do 

 not replace the water each time we stand a good chance of a large proportion 

 of the fertilizer being retained, and a consequent increased growth of plankton. 

 The plankton, however, would tend to be washed out to sea gradually and 

 lost, but some increase may be left to encourage the growth of the bottom 

 fauna and so of the hsh. But how much is 'some'? We do not know, and it 

 would be very difficult to assess the real result in terms offish. Shallow bays 

 are often excellent nursery grounds for flat-fish, but before the fish reach 

 marketable size they migrate to deeper water, and in a bay of this sort there 

 is no barrier to prevent them. Trying to assess the benefit of such a fertiliza- 

 tion would be very like assessing the value of fertilizing a farmer's field by 

 estimating the increased growth of local foxes which had been eating the 

 increased number of rabbits. It miqht be a good thing to do, but considering 

 the small proportion of the fertilizer which would actually become fish flesh 

 it seems rather unlikely ! 



Turning then to the third possibility, that of the open sea, we lose all the 

 disadvantages mentioned for the other two, and we can make some calcula- 

 tions of costs and probable returns. The most important new factor that 

 impresses us in these calculations is the enormous amount of water in the 

 sea even in local areas. Farmers measure their holdings in acres, there are 640 

 acres in a square mile, and a square mile of sea is a very small unit indeed. 

 However, we can use this small unit as a basis for our calculations. Thinking 



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