^ 



Biologi sts are learning more about 

 the effects of high dams on mi- 

 qrating fish from the "beeps" 

 given off hy sonic tags fastened 

 to the fishes' backs 



Getting the Facts 



Government agencies, colleges, and private institutions 

 are engaged in collecting information about the fisheries. 

 The U. S. Bureau of Commercial Fisheries is the agency 

 responsible for the Federal Government's part of this 

 work. Getting these facts requires the services of biolo- 

 gists, chennists, civil, nnechanical, and electronic engi- 

 neers, oceanographers, market specialists, refrigeration 

 specialists, food inspectors, statisticians, economists, 

 trade specialists, linguists, translators, airplane pilots, 

 vessel operators, divers, home economists, law-enforce- 

 nnent personnel, and numerous types of researchers and 

 skilled workers. 



Life history .--One of the first things a biologist wants 

 to learn about a species is its life history: when and 

 where it spawns; conditions affecting hatching and growth; 

 food habits; diseases; natural enemies; life span; years 

 in which it makes its greatest growth; period of best 

 reproduction; period of greatest natural mortality; how 

 it reacts to the environment; and other things. 



For example, if the biologist knows how many years 

 a certain species requires to grow to its most profitable 

 size, and if he knows where and when it spawns, he can 

 study the hatch each year and get information which will 

 help him predict when the catch will be good and when it 

 will be bad. 



But the biologist must also know what factors affect 

 the fish during the nnaturing period. Some fish- -tuna, 

 cod, and haddock for example --deposit their eggs in the 

 open ocean and leave them to the mercy of wind, weather, 

 and ocean currents. Some fish--salmon, for one--move 

 into inland waters and place their eggs in "nests" that 

 the fish brush out of the gravel beds with their tails. 

 Menhaden and shrimp lay their eggs in the open sea but 

 usually the larvae drift into sheltered places in estuaries 

 or along tidal marshes. 



Habitat '--The biologist must learn about the habitat of 

 the fish: where it lives, deep or shallow water; factors 

 that aid or hamper growth, such as salinity of the water, 

 temperature, light, and food supply; factors that affect 

 food supply and tennperature, such as currents and winds; 

 presence of nnineral and other nutrients in the water; 

 conditions that might lead to epidemics; and its predators. 



Hunnan progress has added new habitat problems by 

 damnning rivers and altering watersheds, and by changing 

 coastal nnarshes, either filling or draining them or build- 

 ing canals or other structures. 



Electric shockers ore used to stun 

 fish so that they can be caught, 

 studied, and set free unharmed 



Fish eggs and "fry," or baby 

 fish 



Biologists are finding ways to 

 control drills and starfish--im- 

 Dortant predators on oysters 



