DISTRIBUTION AND DESCRIPTION OF FISHERIES 23 



this "planktonic rain," cannot support plant growth due to a lack of light 

 except in shallow seas. 



The standing crop of phytoplankton must be large to maintain a large 

 stock of small surface animals called zooplankton upon which small 

 pelagic fish may feed. These can be a food source for larger pelagic 

 species or for the demersal fish of shallower seas. Such food chains tend 

 to be long and inefficient as there is great loss at each link. 



Fish production depends upon the rate of replenishment of surface 

 water layers and upon the extent of the shallower water shelf. Practically 

 all harvestable fish stocks are found in the limited oceanic areas where 

 there is substantial upwelling or mixing. Dispersed and economically 

 unfishable stocks are found throughout the oceans where replenishment 

 is slower. 



Replenishment of the surface is effected by upwelling or overturn and 

 to some degree by evaporation or by accretion from nutrient-containing 

 run-off from the land. Upwelling is greatest at divergences of opposite 

 moving water masses or in proximity to land due to offshore w^nds. Replen- 

 ishment also occurs from the slow but massive overturn between the 

 cold waters of higher latitudes and the warmer waters of lower latitudes 

 as well as that which occurs everywhere between winter and summer. 



The fertility of the seas is thus dependent upon immutable geophysical 

 forces such as the earth's rotation, solar radiation, physiography of the 

 bottom, and the distribution of the land masses. 



On land, life processes occur in situ within inches of the surface. 

 Unlike the fluid seas, the growing medium, or soil, is practically stable 

 and resident organisms are accessible. The land can be cultivated and 

 fertilized and the plants and animals domesticated to best suit man's 

 needs. Terrestrial food chains are short, efficient, and can be modified 

 to maximize the food crops, plant and animal. 



Fisheries of the World 



World Production. Commercial fisheries usually develop in countries 

 proximal to productive fishing grounds as with Norway, Canada, Peru, 

 Iceland, and other countries. Also industrialization initially in the United 

 Kingdom and later in most other countries created demand and also 

 facifitated production and distribution. In densely populated Japan a 

 survival need for fish prevailed. A dearth of other exports to balance 

 needed imports has sometimes stimulated fishing as in Iceland. 



Production by Continents. The recent world production* by continents 

 has been as follows, in billions of pounds. 



* Food and Agriculture Organization, 1959. 



