194 THE PRODUCTIVITY OF THE SEA [PART II 



Uncultivated mussel beds (Conway)^, 



4,033 kgs. mussel flesh per hectare ; 



Uncultivated inshore general sea fisheries (Morecambe Bay), 



89 kgs. fish and shellfish per hectare ; 



Uncultivated North Sea fishing grounds, 



17*6 kgs. fish per hectare. 



(2) In terms of dry organic substance: 



Cultivated land (Biebahn and Rodewald), 

 1,790 kgs. per hectare ; 



Cultivated mussel beds (Morecambe), 

 1,140 kgs. per hectare; 

 Uncultivated sea (Baltic), yield in plankton (Hensen), 

 1,500 kgs. per hectare. 



From these figures it appears that the produce of a large 

 uncultivated water area is less than that of a cultivated land area, 

 whether we take the yield in fish or shellfish flesh, or the yield in 

 dry substance as the basis of comparison. But a cultivated water 

 area, such as a fresh-water carp-pond, or a part of the sea near the 

 shore treated so as to produce shellfish under the most favourable 

 conditions, is capable of affording a rich " crop " ; and if aquiculture 

 were as intelligently studied and practised as agriculture there 

 can be little doubt that the sea would be more productive than the 

 land. Thus Hensen estimated that the mass of plankton (ultimate 

 organic substance) produced in the uncultivated Baltic was not far 

 short of that produced upon cultivated land. 



Let us attempt to compare the nature and density of life on 

 a land surface in the temperate zone, with a sea surface of corre- 

 sponding extent. If we were to explore a large tract of cultivated 

 and forest land, in which crop-lands, meadows, woodland, streams, 

 and moorland occurred, we should find that everywhere vegetable 

 life would be predominant, and that animal life would be com- 

 paratively sparsely distributed. Overhead in our meadow land and 

 in the cultivated parts would be a few birds and insects, while in the 

 soil and on the vegetation there would occur insects, worms, and 

 here and there rodents like mice and rabbits. In the woodland 



1 Taking the weight of flesh in a mussel as 37 "/o of the total weight. 



