180 THE OCEAN RIVER 



ing down to form enormous sieves. Tons of water are taken 

 into the mouth and then forced through the whalebone 

 strainers by means of the huge tongue, which then scrapes the 

 plankton off and thrusts it into the gullet. The horny fringe is 

 thus a natural plankton net which serves to filter out the mil- 

 lions of small Crustacea that make up the diet of both right 

 whales and rorquals. The infinite numbers of tiny Crustacea 

 needed to sustain the large bodies of whales, weighing hun- 

 dreds of tons, gives a measure of the prodigious quantities of 

 plankton in salt waters. 



Whales do not feed intensively all the year round although 

 their rate of growth is colossal. In the summer they find their 

 food in the colder subpolar waters in the form of great swarms 

 of euphausids (small shrimplike Crustacea with branching 

 legs), still smaller Crustacea known as copepods, and small 

 drifting shellfish called pteropods. In the North Atlantic they 

 may even strain small herring out of the water. In the winter 

 they travel south, and at one time were the object of whale 

 fisheries along the coasts of Portugal, North Africa, and the 

 Azores. While wintering in tropical and subtropical waters 

 they find little to feed on, since nowhere does plankton grow 

 as richly as in the colder seas. During the winter their gargan- 

 tuan matings take place, for they are in all respects mammals 

 in spite of their fishlike habits and appearance. Few whales 

 give birth to more than five calves during their lifetime, and 

 the calves are helplessly dependent on their mother's milk 

 during the first six months of their lives; thus it is not surpris- 

 ing that their reproduction could not keep pace with the 

 inroads made by uncontrolled whaling. The modern 20,000- 

 ton factory ships are equipped to handle together as many as 

 40,000 whales a year, which is uncomfortably close to the 

 natural rate of replenishment. 



The complex economies of the great civilizations that have 

 grown up around the River are no more involved than the 



