fort, as quantified by Griffin (1978) 

 (positive relationship). The equa- 

 tion explains 88 percent of the var- 

 iation in brown shrimp landings. 



Van Sickle et al. (1976) ex- 

 amined oyster production in the es- 

 tuaries of the Barataria basin as 

 related to salinity levels. They 

 found that optimal conditions for 

 oyster production existed within a 

 salinity band which moved upstream 

 when salinities increased in the in- 

 ner bays. They said the oyster in- 

 dustry could be destroyed if oyster 

 habitat is pushed into upstream areas 

 of urban and industrial pollution. 

 The increasing salinities are attri- 

 buted to land losses and changes in 

 Mississippi River flow, both of 

 which result from natural and man- 

 made causes. 



The band of optimum salinity 

 conditions for oysters was found to 

 be in the 10-15 ppt range in the area 

 just east of the Mississippi River by 

 Breithaupt and Dugas (1979), who say 

 that oyster larvae are killed below 

 10 ppt, while the oyster drill, a 

 major predator of oysters, is intol- 

 erant of salinities below 15 ppt. 

 Lindall et al. (1972) consider the 

 oyster to be a good indicator spe- 

 cies for the determination of the 

 optimum salinity range for Louisi- 

 ana estuarine fisheries in general. 

 Although Mississippi River flood 

 waters, such as those of 1973, cause 

 extensive oyster mortalities, oys- 

 ter populations appear to thrive 

 in years immediately following such a 

 flood (Dugas and Perret 1976) , per- 

 haps because oysters can become 

 reestablished more quickly than their 

 parasites and predators. 



The Mississippi River delivers 

 272 million metric tons of sediment 

 annually to Louisiana's deltaic 

 coastal area and is responsible for 



building and maintaining the coastal 

 marshes (Gagliano and van Beek 1976), 

 which are the most extensive per unit 

 coastline in the United States. Flow 

 diversions have diminished the riv- 

 er's marsh-building capability by 

 depositing approximately 80 percent 

 of the sediment load at the edge of 

 the shelf, where it no longer con- 

 tributes to building marshes. Natu- 

 ral processes such as subsidence and 

 sea-level rise are causing a loss of 

 intertidal land not counteracted by 

 sedimentation. An average land-loss 

 rate of 42.7 km /yr was calculated 

 by Gagliano and van Beek (1970). 

 Due to anthropogenic activities such 

 as drainage and spoil disposal, loss 

 of wetlands is even greater (Craig 

 et al. 1979). Coastal wetlands are 

 important to fishery productivity. 

 On a world-wide basis, Turner (1977) 

 has demonstrated a relationship be- 

 tween shrimp yield and area of in- 

 tertidal vegetation, adjusted for 

 latitude. Faller (1979) has shown 

 that local shrimp production gives 

 a good fit to a function of shore- 

 line density (the ratio of marsh- 

 water interface to area of water) in 

 Louisiana, which is the leading 

 state for commercial shrimp produc- 

 tion. These findings suggest that 

 sediment deposition by rivers may 

 be a critical factor in estuarine 

 fisheries production. 



TEXAS 



Texas has diverse estuarine 

 conditions and related problems be- 

 cause of climatic variation. The 

 upper Texas coast has high rainfall, 

 while the south coast is semi-arid. 

 Current and potential problems for 

 many of the estuaries are associated 

 with increasing municipal and indus- 

 trial water consumption and with the 

 diversion of fresh water from one 



413 



