IV-83 



DEPENDENCE OF FISH AND SHELLFISH ON THE ESTUARINE ZONE 



Dependency 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 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 re- 

 turn to the estuarine zone and the sea. The young of all 

 anadromous species spend varying periods of time in the 

 freshwater areas where they were spawned, but all eventually 

 migrate to the estuaries and then the sea. 



There are few truly catadromous species that mature in 

 the fresh or brackish water environments, and then migrate 



