112 



set in shallow water. The waters in these estuaries provide an abun- 

 dance of food for the salmon in the form of the young sea herring and 

 euphausiid shrimp. 



All five species of salmon on the west coast have one basic difference 

 from the Atlantic salmon. They die subsequent to spawning. The 

 total spawning range of these species is from Monterey Bay, Calif., to 

 the northwest tip of Alaska. Only the King salmon occupies the 

 spawning streams of the full range. The Silver salmon has the next 

 longest range along the coast extending from the Sacramento River 

 to the Bering Strait. The Red, Pink, and Chum salmon range from 

 Washington State to the Bering Sea, and are rarely found south of this. 



The distance upstream that the Pacific salmon migrates to spawn 

 varies from species to species, as well as within species, varying from 

 the extreme headwaters 1,500 miles from the estuarine zone to within 

 a few miles of the estuary. Both the young and adult salmon of all 

 species pass through the estuarine zone, either to reach the spawning 

 ground in fresh water or to reach the sea. During the passage through 

 the brackish estuary the adult ceases feeding, whereas the young of 

 all species utilize the food available in the estuarine zone as they pass 

 through to reach the sea. Young Silver salmon are known to remain 

 within the estuarine portions of their natal stream, growing rapidly 

 on the abundant food supply in this highly productive environment. 

 Adult Silver salmon are caught throughout the year within the estu- 

 arine zone. The Pink salmon fry enter the brackish estuarine waters 

 soon after hatching in the Spring, and are known to remain there until 

 August. 



OYSTERS 



The Atlantic oyster has evolved into an animal of broad adaptability 

 relative to salinity, temperature, and food requirements, as indicated 

 by its range, on the Atlantic and gulf coasts of North America from 

 the Gulf of St. Lawrence to the Mexican coast. 



The Atlantic oyster is most abundant in estuarine systems charac- 

 terized by considerable inflows of fresh water, with constant water 

 movement, and fluctuating local salinities. The currents bring food 

 to these fixed animals and distribute the larvae. Two of the most pro- 

 ductive areas for the Atlantic oyster are the Chesapeake Bay and the 

 Louisiana bays and sounds affected by the great flow of the 

 Mississippi River. 



The salinity range most favorable to the Atlantic oyster lies between 

 five and 30 parts per thousand. Below five little or no reproduction 

 takes place and the feeding ability is affected. Oysters occupying 

 areas with salinities exceeding 15 parts per thousand are subject to a 

 number of predators such as the oyster drill. 



The Atlantic oyster has adapted to wide ranges of temperatures. 

 It survives in temperatures of around 34° F. and in temperatures of up 

 to 90° F. Intertidal oysters in the warm climate of Texas survive a 

 number of hours out of the water with internal temperatures of as 

 much as 120°F. This oyster ceases feeding when temperatures fall 

 below 43°F. or rise above 107°F. Oysters spawn only when the 

 temperature of the water rises above 68°F., whether in Long Island 

 Sound or Apalachicola Bay. In its southern range the oyster has a 

 much longer spawning period and feeds all year long. 



