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propagation, growth, and survival; and, for some life forms, 

 bottom conditions suitable to their unique needs. 



The dependence of fish and shellfish on the estuarine zone is 

 governed by particular environmental requirements for reproduction, 

 protection, food supply, or a combination of these. Estuarine 

 dependent species are of three types: 



1 . Species Restricted to Estuaries 



Among the relatively few species of fish and shellfish 

 that complete their entire life cycle in the estuarine 

 zone is the Atlantic (American) oyster. It will die 

 after long exposure to freshwater although it can stand 

 limited periods of such exposure and can thrive in 

 relatively high salinity water. The spotted sea trout 

 occupies the estuary for all its life purposes and only 

 occasionally leaves the estuary under unusual extremes 

 of salinity and temperature. 



2. Anadromous and Catadromous Species 



Anadromous species pass through the estuarine zone on 

 their journey from the sea to the freshwater environment 

 where they spawn. Some species, such as the Pacific 

 salmon, die after spawning and others, such as the 

 striped bass, live to return to the estuarine zone and 

 the sea. The young of all anadromous species spend 

 varying periods of time in the freshwater areas where 



