THE AGE OF FISHES 175 



In the enormously varied zoo of the plankton the giants are 

 jellyfish and Portuguese men-of-war, which trail their stinging 

 tentacles behind them. Barely large enough to see are minute, 

 many-legged crustaceans with voracious appetites, swimming 

 in spasmodic jerks like strange monsters from another world, 

 side by side with fierce-jawed arrow worms, long and stream- 

 lined. Plankton is the nursery of nearly all ocean life, for in 

 it there float baby crabs with projecting spines many times 

 the length of their bodies, and the young of spiny lobsters, 

 flat, transparent, and leaflike, with spiderlike legs and eyes on 

 stalks. Drifting helplessly along with them are large-eyed, 

 transparent, newly-hatched fishes. These miniature monsters 

 of the plankton live in part on each other, but the smaller 

 of them are grazers, and feed only on the tiny drifting plants. 



Some fishes are plankton feeders; and even some of the 

 whales, largest of all living animals, live entirely on the drifting 

 organisms in the plankton. In contrast to these are the car- 

 nivorous fish. They prey on other fish which are plankton 

 feeders or which rely in turn for their food on plankton feed- 

 ers. Thus directly or indirectly the richness of life in the ocean 

 depends on the richness of its plankton growth, much as the 

 food of mankind is limited by the success or failure of the 

 corn crop and by the extent and richness of the pasture lands 

 on which livestock graze. And so the Age of Fishes is still 

 very much an Age of Plankton. Those who sought to find the 

 secrets of how and why our fisheries are linked to the move- 

 ments and pulses of the Ocean River soon found that plank- 

 ton was a fundamental part of the answer. 



Although plankton plays such a vital role in the life of the 

 ocean, this was virtually unsuspected until as recently as about 

 100 years ago. It is true that from the earliest times men 

 have noticed the occasional red, green, or yellow discolorations 

 of sea water caused by excessive concentrations of plankton. 

 Whaling skippers had long been aware that a good catch 

 might be presaged by the appearance of the small, shrimp-like 



