184 THE OCEAN RIVER 



manner of life existed in the open sea. With advancing knowl- 

 edge the front of scientific attack soon shifted from the ques- 

 tion of 'Vhat" to the questions of ''how" and ''why." Today 

 it is mainly concerned with the intricate relationships among 

 the different types of life, with the quantities and numbers 

 and rates of growth in the food chain which are at the root of 

 ocean economics, and with unravelling the complicated effects 

 of water currents upon them. 



We already have some rough answers, though our marine 

 accounting is still in its infancy. Johannes Peterson of the 

 Copenhagen laboratory has estimated that ten tons of plant 

 or animal food are needed to produce one ton of fish. One ton 

 of carnivorous fishes like codfish may consume ten tons of 

 plankton feeders, as for example young herring, and these in 

 turn may eat 100 tons of plankton. There may be still other 

 links in the chain. The net result is that when a trawler brings 

 back its catch each ton of seafood landed is the end result of 

 a growth of considerably more than 1,000 tons of microscopic 

 plant cells. The total annual world catch of food fish is some- 

 thing like 1 3 million tons, so that the plankton production is 

 at least 13,000,000,000 tons in the comparatively small areas 

 of the ocean to which commercial fishing is restricted. We do 

 not know how many tons of cod may be eaten by a hungry 

 New Englander, but it is clear that the plankton could support 

 a good proportion of the world's population. 



In these days of a rapidly growing world human population 

 and a lagging food supply it is tempting to consider the possi- 

 bilities of harvesting plankton directly, so that full advantage 

 might be taken of the great food potentialities of the ocean. 

 Scientists in several countries have in fact attempted to devise 

 efficient methods of extracting plankton from sea water. Un- 

 fortunately, nothing practical has yet come of it. Plankton is 

 fishy to the taste and not particularly palatable, but it would 

 probably make excellent cattle food. The real difficulty, how- 



