THE OCEAN FEEDING-GROUNDS 99 



cannot exceed the total mass of plankton itself. We 

 might therefore legitimately estimate the total produc- 

 tivity of any marine area by the method of Hensen ; 

 that is to say, by measuring the amount of plankton 

 taken at different points under different conditions and 

 at different seasons ; but we must make our count with 

 the utmost patience, in order that we may distinguish in 

 our measurements and our calculations the producers 

 (algae) from the consumers (animals). The quantity of 

 plankton contained in the water at the beginning of 

 the year represents, in fact, a capital sum of which the 

 interest only is consumed during the course of the 

 year in the shape of products, and which should be 

 still intact at the end of the year. 



Revenue. 

 Fish and other species. 



Capital. ^\ 



Plankton A. Plankton A. 



January ist. December 3ist. 



As an example, let us estimate the number of seals on 

 the Californian coast at 25,000. Each seal eats about 

 44 Ibs. of fish per diem. If we admit that 44 Ibs. of fish 

 are the product of 44 Ibs. of plankton daily, the 25,000 

 seals indirectly consume about 401,500,000 Ibs. of plank- 

 ton. Before the end of the year this enormous quantity 

 is restored by recuperation. 



When we have a perfect knowledge of plankton we 

 shall be able to determine whether there is any possi- 

 bility of augmenting the fertility of the seas by human 

 intervention, as cultivators enrich the soil with manures. 

 But hitherto we have not reached the necessity of such 

 a procedure, judging, at least, from the North Sea. 



