creates a nutrient sink of sulfates, 

 carbonates, phosphorus and nitro- 

 genous compounds (Copeland 1966) . In 

 addition, large amounts of detritus 

 are washed into the estuary by the 

 river flow. This detritus is a 

 principal element in the food web of 

 estuarine ecosystems (Copeland 1966). 



There is some evidence that 

 the various species of shrimp dif- 

 fer in their affinity to freshwater 

 inflow as it is translated into sa- 

 linity regimes. In fact, Gunter et 

 al. (1964) have shown that salinity 

 may be a limiting factor in the dis- 

 tribution and abundance of the com- 

 mercially important penaeid species. 

 In their studies, juvenile P. az- 

 tecus were most abundant in es- 

 tuarine waters of 10 to 20 ppt sa- 

 linity whereas P. setiferus were 

 more abundant in waters below 

 10 ppt and P. duo ra rum tended to 

 reach a larger abundance in waters 

 greater than 18 ppt. These ob- 

 served preferences are clearly de- 

 picted in species composition of 

 the catch. Statistics tend to 

 show the greatest concentration of 

 brown shrimp to be off Texas where 

 bay salinities are generally high- 

 er. In Louisiana white shrimp are 

 dominant due in part to the rela- 

 tive freshness of the inside wa- 

 ters, while pink shrimp appear to 

 be more abundant in the catch off 

 southern Florida where salinities 

 approach oceanic conditions (Gun- 

 ter et al. 1964). Gunter and 

 Hildebrand (1954) showed a correla- 

 tion between the catch of white 

 shrimp on the Texas coast and the 

 average rainfall for the State. 

 Their results show a significant 

 correlation between the rainfall of 

 the previous two years and the 

 catch of white shrimp. Copeland 

 (1966) also showed that an increase 

 by similar fluctuations in shrimp 



catch, generally after a two year 

 period. 



Williamson (1977) stated that 

 in San Antonio Bay, brown shrimp 

 abundance in May through July was 

 not affected by inflows in the May 

 to June period or those from the 

 previous September and October time 

 frames. White shrimp on the other 

 hand did vary positively in August 

 with increases in the spring in- 

 flows. There also appeared to be 

 some enhancement of white shrimp 

 numbers by fall inflows of the pre- 

 vious year. 



White and Perret (1973) show- 

 ed that the timing of inflow is 

 also important. In their eval- 

 uation of the effects of the 

 Toledo Bend Project on Sabine 

 Lake, they attributed the reduc- 

 tion in catch for the brown and 

 white shrimp to operational pro- 

 cedures of the dam. Historically, 

 heavy discharges occurred during 

 spring and tapered off during the 

 summer. The operating procedures 

 of the dam changed this pattern 

 by holding back the inflow surge 

 until mid-May. This alteration 

 has produced a near freshwater sit- 

 uation within Sabine Lake which 

 has devastated the brown and white 

 shrimp populations. 



IMPLICATIONS TO PLANNING 



AND MANAGEMENT 



There continue to be ever in- 

 creasing demands for the available 

 surface water. Frequently the 

 need to allocate water to the es- 

 tuary is overlooked. Fortunately, 

 it appears that many water mana- 

 gers now see the need for consider- 

 ing freshwater and associated nu- 

 trient flows into the marsh areas to 



433 



