CHAPTER 10 



Phiiiktoii and its relationship with tJic fisheries 



It will have been realized, from the preceding chapter in particular, that the 

 food supply of the fish themselves is fundamentally the phytoplankton, so 

 that the importance of plankton to the fisheries is indeed basic. This is true 

 whether the fish are plankton feeders like the herring, bottom feeders like 

 plaice, or really deep-sea fish like halibut. The relationship has been nicely 

 depicted by Professor Hardy, and his figure is reproduced here as Fig. 32. 



Fic. 32. A diagraniiuatic sketch illustrating the general economy of the sea. From Hardy. 



It has, too, already been explained that the richness of plankton production 

 depends on the mixing of the waters so that nutrient-rich water from the 

 deeper layers is brought to the surface layers where the plants can use it. The 

 intimate chemical and biological factors in the history of the water have their 

 importance in the succession of the various plankton species with their 

 different food values or availability as food. In the higher latitudes plankton 

 is richer in food value than in the tropics (Fig. 30). It is thus no accident that 

 the richest fisheries of the world are related to. the areas of richest plankton 

 production and arc on the continental shelves, where there is good feeding 

 and depths which can be economically tished. 



There are a number of aspects of this relationship that are worth further 



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