Biologists tog lobsters to learn 

 rr.ore about them, such as now 

 lonr; they live, how fast they orow, 

 and how for they travel 



S*^^ 



SCUbA divers have learne-' n^jny 

 things abo'jt fish and fis^'in;j 



S2~-: 



Biologists are studying the green 

 crab, which in recent years hos 

 become on i'Tiportant predator on 

 softshell clams 



Plankton, floating plants and ani'iials so 

 tiny we cannot see them with the naked eye, 

 are food for bony fish, sor^e whales, sharks, 

 nn-' other aquatic animals 



The food C/Zflin« --Pl^ri^ton is the beginning of nnost food 

 chains. Composed of small, sometimes microscopic, 

 plants and animals, it is food for small aquatic animals 

 which in turn are food for larger aquatic animals. It 

 depends on nninerals and other nutrients in the water 

 and on light and temperature to svirvive. Some of the 

 minerals are carried to the rivers by runoff; the rivers 

 carry some to the ocean. Other minerals have been in 

 the ocean for ages and are brought up from the lower 

 le\'els by "upwellings,' ' or water currents that rise to 

 the surface. The minerals are then spread over wide 

 areas by wind and ocean currents. Hence, temperature 

 studies, water samples for chemical content and plankton, 

 and knowledge of "drift" or water movement produce 

 important information. 



Taggitlg' --T^gg^T^g fish is as important to fishery 

 research as banding ducks is to waterfowl studies. Various 

 kinds of tags are used--small metal disks, plastic loops, 

 small capsules, and plastic darts. Sometinnes a small 

 metal tag is placed in the abdomen of a fish; electric 

 detectors must be used in these cases. Research is being 

 done on radioactive tags. Tagging not only tells us how 

 fish migrate but also allows biologists to estimate total 

 numbers present and the proportions that are caught or 

 escape to spawn. 



Color marking-- -Dye is used for marking shrimp be- 

 cause tags are lost when the shrimp sheds its old shell. 

 The color remains in the head for several months. 



Underivater television and SCUBA divers. --It is now 

 possible to observe consistently for the first time in 

 history just how fishing gear operates under water, to 

 make recommendations to improve gear, and to study the 

 effect of gear on fish. These studies can lead to more 

 efficient gear and less waste of the fishery resource. 



Chemical aids. --After testing 5,000 chemical formula- 

 tions the Bureau of Commercial Fisheries found a "selec- 

 tive" poison which will kill sea lamprey larvae and not 

 harm desirable fish, paving the way to restore Great 

 Lakes trout fisheries. Selective chemicals to control green 

 crabs (clam predators) are also being studied. This is a 

 field of great promise. 



Electrical aids. --These aids include fish finders to 

 locate fish; telemeters to give the location of a fish trawl 

 in the water; electrical fences that kill unwanted fish; 

 cameras with which the fish takes its own picture; ap- 

 paratus by which fish count themselves as they move up 

 and down stream; a "sonic tracker," an inch-long tube 

 attached to the fish which sends out "beeps" for hours. 

 Researchers are perfecting electrical fences that will 

 guide fish away from danger spots, as turbines and intakes 

 at dams, and a device by which the fish will "tag" them- 

 selves by triggering an identification dart as they swim 

 past. 



