372 



CONSERVATION AND ITS LESSONS 



Conservation of Ocean Fishes. — We have just seen that the 

 relation of fish Hfe to their natural food is an important factor in 

 preserving our supply of fish, especially in inland waters. The 

 balance of life is equally important for fish in the ocean. It is 

 one of the greatest problems of our Bureau of Fisheries to discover 

 the relation of various fishes to their food supplies so as to aid in 

 the conservation of life in our lakes, rivers, and seas. 



Migration of Fishes. — Some fishes change their habitat at dif- 

 ferent times during the year, moving in vast schools northward in 

 the summer and southward in the winter. In a general way such 



migrations follow the 

 coast lines. Examples 

 of such migrator}^ fish 

 are the cod, menhaden, 

 herring, and bluefish. 

 The migrations are 

 due to temperature 

 changes, to the quest 

 of food, and to the 

 spawning instinct. 

 Salmon and some other 

 fish pass up rivers to 

 spawn ; the eel, on the 

 contrary, leaves the 

 rivers and spawns in 

 the ocean. Some fish 

 migrate to more shal- 

 low water in the sum- 

 mer, and to deeper water in the winter ; here the reason for the 

 migration is doubtless the change in temperature. All of these 

 habits are studied by the fishermen, who are thus able to catch fish 

 where and when they are most plentiful. The cod and herring 

 fisheries are notable examples. 



The Egg-laying Habits of the Bony Fishes. — The eggs of most 

 bony fishes are laid in great numbers, varying from a few thousand 

 in the trout to many hundreds of thousands in the shad and several 

 millions in the cod. The time of spawning is usually spring or 

 early summer. After the eggs are laid the male fish usually 



Development of a trout. 1, the embryo within the 

 egg ; 2, the young fish just hatched, with the yolk 

 sac still attached ; 3, the young fish. 



