should be taken only from the bachelors. By weeding them out 

 there were fewer casualties, especially among the pups, and the 

 numbers killed for commercial purposes were more than offset by 

 the saving of life by reducing the number of fights. So were saved 

 the immense breeding colonies of the Pribilof seals, one of the 

 natural wonders of the world. 



Once this principle had been established it could be appHed 

 elsewhere, because the breeding behavior of seals follows much 

 the same pattern whatever the species. The numbers in the harems 

 may differ with different species, and there are other variations in 

 behavior besides, but the principle used in this conservation with 

 exploitation - a perfect example of having your cake while eating 

 it - has been applied to other species, notably to the southern sea 

 elephant. This animal was once abundant on the many islands in the 

 sub-Antarctic, but commercial killing had all but wiped the sea 

 elephant out on some islands and reduced them everywhere to 

 dangerously low levels. The numbers are now ever5rwhere on the 

 increase. For fishes, conservation depends on a knowledge of the 

 food supplies available for the different species, as well as their 

 breeding habits. Mackerel, for example, depend at one stage of 

 their Uves on shrimps, worms, and small fishes. But these in turn 

 must depend on smaller organisms, whether very small animals or 

 plants. 



But it is not enough merely to study the food of fishes to ensure 

 good harvests from the sea. We must also take into account physical 

 aspects of the sea itself. Temperature, for instance, can play a very 

 important role. A striking example of this is in the story of the 

 tilefish. The particular species in question grows to a length of 

 two feet and lives beneath the Gulf Stream along the seaboard of 

 North America at depths of forty-five to a hundred fathoms, where 

 the temperature is from 8°c. to iz°c. In 1882 the warm water 

 was displaced by an unusually strong wedge of cold water from 

 the Labrador Current coming down from the north. That same 

 year a ship's captain looked out across Delaware Bay one early 

 morning and saw mile after mile of dead and dying tilefish — the 

 estimated death toll was six times the total annual catch of all fish 

 in the United States. The drop in temperature of the water had 

 done its deadly work ; for all time, some people thought. The tile- 

 fish was not quite extinct, although thirty-five years were to elapse 

 before they were caught again in large numbers. 



Almost as deadly as the influx of cold water, and in many ways 

 more spectacular, are the so-called "red tides." They are caused by 

 abnormally high concentrations of microscopic plant-animals, dino- 

 flagellates, most of which are less than one thousandth of an inch 

 across. These plant-animals are usually present in the plankton in 

 smaller numbers than the diatoms. They differ from the diatoms by 

 having an outer casing of cellulose (instead of siUca) or no casing 

 at all. In the warmer waters a "tide" occurs when the diatoms 

 become less plentiful and their place is taken by vast numbers of 

 dinoflagellates. When this happens the sea may be colored red for 

 miles. Such growths have given the Red Sea its name. When, as 

 happened in 1947 off the west coast of Florida, their numbers rise 

 there may be fifty million or more to each pint of sea water. The 

 sea becomes slimy to the touch and highly poisonous to fish. The 

 red tide off Florida in 1947 killed upward of fifty million fish. 



Mass fish kills known as "red tides" have 

 been known since biblical times. Some 

 are caused by abnormally tiigh concentrations 

 of a dinoflagellate called Gymnodinium brevis 

 (magnified about 1700 times). During a red 

 tide millions of dead and dying fish are 

 washed up onto the beaches. Exactly how 

 they are killed is still not known. 



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