^ 



TUNNY 



length about 8 feet 



HERRING 



length about 9 inches 



The Movement of Fishes 



Two tons of fish - cod, haddock, halibut, and 

 skate - are dumped onto the deck of a British 

 trawler fishing in the Barents Sea. The 

 temperature of the water, its salt content, 

 and the migration habits of fish are all 

 important factors that determine the 

 distribution of fish. The more the commer- 

 cial fisherman knows about them, the better 

 his long-term catch will be. 



Fishes are about as much tied to temperature as is plankton. 

 The different kinds of sardine, for example, are Uixiited in both 

 Southern and Northern hemispheres to waters between i2°c. and 

 20° c. Dangerous sharks, found all the year round in tropical seas 

 I between latitudes 2i°N. and 2i°S., are likely to do some traveling 

 during the hot summer months. With a rise in the temperature of 

 the water, they have been kno-wn to attack swimmers as far north 

 or south of the Equator as 42°. 



Temperature is only one of the factors that determine the range 

 over which a species may be distributed. There are many others, 

 and the more the fisherman knows about them, the better his long- 

 term catch will be. Because we know that the sardine makes a 

 breeding migration from the southern end of the Bay of Biscay to 

 the English Channel and then returns south, the sardine fishery 

 sensibly moves with the fish. Similarly, men have learned that the 

 so-called Mediterranean tunny makes its home in the Atlantic, to 

 the west of Spain and Portugal, as well as in the Mediterranean. 

 (There is also a subspecies - the tuna - on the American side of the 

 North Atlantic.) The tunny spawns off the Azores, off Gibraltar, 

 and in the western Mediterranean along the coasts of Sardinia, 

 Sicily, and Tunisia. 



After the spawning migrations-; large numbers of the tunny move 

 north. They pass to the west of the British Isles, round the north 



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