THE CONSERVATION OF SHELLFISH 371 



charged into a river untreated, the organic matter absorbs much 

 or all of the dissolved oxygen in the water. But this oxygen is 

 absolutely essential for plant and animal life. Oil wastes poured 

 out by oil-burning steamers are becoming a nuisance along our 

 shores and are responsible for the death of many food fish. If 

 our fish and other water animals are to be preserved, we must 

 stop the pollution of our national waterways. Dr. Henry B. Ward 

 is authority for the estimate that if rivers now polluted with sewage 

 and factory wastes were clean again they would put $100,000,000 

 a year into the pockets of taxpayers from the sale of marketable 

 fish. In addition to this would be the sport of thousands of fisher- 

 men and other thousands who would use the rivers for boating 

 and bathing. 



The Conservation of Shellfish. — The problem of conserving 

 shellfish is concerned in part with the extermination of their 

 natural enemies. If we could kill off all starfish and boring mol- 

 lusks, the oysters and clams would be much more plentiful. But 

 over-fishing is the most important danger. The oysters of Chesa- 

 peake Bay were thought inexhaustible until they were almost 

 fished out. Then the state of Maryland discovered that oyster 

 culture was necessary if this great asset was to be preserved. 



Oysters pass the first few days of their existence as free swimming 

 larvae. Then they settle on the bottom, and if they do not find 

 some solid object which raises them above the mud of the bottom, 

 they will die. Oysters are now protected by cultivation ; on the 

 bottom, in certain areas of shallow water, are placed bunches of 

 twigs, broken rocks, or old oyster shells to which the young oysters 

 attach themselves. After they have grown to approximately the 

 size of a quarter or half dollar these '' seed " oysters are spread over 

 the bottom of the oyster beds, and later are harvested. 



Clams and scallops have been nearly depleted in some areas, 

 and it has become necessary to conserve the supply by having 

 closed seasons and by transplanting the " soft clam " of the east 

 to the Pacific Coast, where it thrives. 



Lobsters are being conserved by taking the fertilized eggs and 

 raising the young in hatcheries until they are large enough to care 

 for themselves. This artificial protection lasts only while they are 

 free swimming larvse. 



