A NEW APPROACH TO DETERMINING THE 



QUANTITATIVE RELATIONSHIP BETWEEN 



FISHERY PRODUCTION AND THE FLOW 



OF FRESH WATER TO ESTUARIES 



Joan A. Browder 



Office of Fishery Management, Southeast Fisheries Center 

 National Marine Fisheries Service, Miami, Florida 



Donald Moore 



Environmental Assessment Branch, Southeast Region 

 National Marine Fisheries Service, Galveston, Texas 



ABSTRACT 



Freshwater inputs to estuaries 

 appear to enhance the production of 

 marine organisms, because the highest 

 marine standing stocks along shore- 

 lines are found in or near estuaries, 

 which receive freshwater inputs. 

 Despite this apparent connection, ef- 

 forts to quantify the role of fresh- 

 water in estuarine production not 

 only have contradicted one another 

 but have, in some cases, been con- 

 tradictory to the basic concept of 

 the value of freshwater inflows to 

 estuarine production. In this paper 

 we describe the water regimes, water 

 management problems, and related 

 estuarine research of several dis- 

 tinct regions of the Gulf of Mexico, 

 from south Texas to south Florida, 

 and then suggest an approach to ex- 

 amining the role of freshwater in 

 estuaries that could lead to a uni- 

 fying principle applicable to all 

 situations . 



INTRODUCTION 



Coastal areas receiving fresh 

 water are important to the production 

 of fish and shellfish. The relation- 

 ship between freshwater inflow and 

 production is recognized but has been 



difficult to quantify. Fishery man- 

 agers have few guidelines and little 

 information to evaluate the effect of 

 water management projects on fish- 

 eries, but they must decide how much 

 water can be diverted or how much the 

 seasonally of flow can be altered 

 without reducing estuarine produc- 

 tivity. 



"Production functions" quanti- 

 tatively relating fish production to 

 freshwater flow under various circum- 

 stances are needed. Although the 

 functions may differ for each estu- 

 ary and each species, determining 

 such functions for even one estuary 

 would be valuable in establishing a 

 methodology. Determining production 

 functions for several estuaries may 

 lead to the development of a genera- 

 lized model applicable to any estu- 

 ary. Such a model surely must incor- 

 porate hydrologic, meteorologic, and 

 hydrodynamic concepts as well as 

 physiological and ecological informa- 

 tion and will therefore require an 

 interdisciplinary effort. 



This paper will (a) provide a 

 brief history of scientific work done 

 in the Gulf of Mexico that relates to 

 this problem; (b) summarize some re- 

 cent work in Florida, Louisiana, and 



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