estuaries in harvests of oysters, 

 blue crabs, and white and brown 

 shrimp (National Marine Fisheries 

 Service 1962-1977a). This estuary 

 provides over four-fifths of the oys- 

 ters and one-third the blue crabs in 

 the entire Texas landings and nearly 

 half of the shrimp caught in the 

 Texas bays. It provides a larger 

 catch of oysters and shrimp per unit 

 area than any other Texas estuary. 

 The importance of the Trinity River, 

 the predominant source of fresh water 

 for this estuary, was underscored by 

 Cooper and Copeland (1973), who 

 reported on results of a simulation 

 model of Trinity Bay that related 

 water exchange and retention char- 

 acteristics of the bay to biological 

 activity. They stated, "Our data 

 indicate that reduction of normal 

 Trinity River flows or addi- 

 tions of industrial effluents, or 

 both, would result in reduction of 

 estuarine community respiration 

 rates. These reductions, indicative 

 of decreased organic consumption 

 rates, would lead to less producti- 

 vity in Trinity Bay. Since Trinity 

 Bay (as a major part of the most val- 

 uable Texas estuarine system) is a 

 major nursery ground and supports 

 significant populations of valuable 

 organisms, reduction in river flow 

 or addition of additional effluents, 

 or both, would have a significant 

 negative impact on fisheries and 

 tourism economies of the Texas 

 coast" (Cooper and Copeland 1973: 

 234). 



return flows from Houston metroplex. 

 Maintenance of adequate quality of 

 the return flows may become critical 

 because they probably will continue 

 to increase as a result of the ex- 

 plosive population growth in the ar- 

 ea. If adequate quality is main- 

 tained, some of the adverse impacts 

 of diversion of San Jacinto and low- 

 er Trinity River waters for use in 

 Houston may be avoided. However, the 

 ability of the ecosystem to assimi- 

 late a given quantity of pollutants 

 is reduced with the reduction of 

 freshwater. Detrital and sediment 

 in-flows will probably be reduced as 

 freshwater inflows are reduced. 



A draft report on the Trinity- 

 San Jacinto Estuary by the Texas De- 

 partment of Water Resources (1979b) 

 indicated that current fishery har- 

 vests in the estuary could be main- 

 tained, and even slightly increased, 

 with only three-fourths of the cur- 

 rent average (four-fifths of the me- 

 dian annual inflows. This predic- 

 tion is based on a model of commer- 

 cial catches of selected species in 

 the estuary. The model considers on- 

 ly environmental factors, but catch 

 also is determined by numerous non- 

 environmental influences, such as 

 price paid for the catch, cost of 

 fuel, attractiveness of other fish- 

 eries, and fishing regulations. 

 Such non-environmental factors would 

 have less influence if catch-per-unit 

 effort rather than total catch were 

 predicted by the model. 



Water from both the Trinity 

 and San Jacinto Rivers is heavily 

 utilized by metropolitan Houston. 

 With the existing Livingston reser- 

 voir, utilization of Trinity River 

 water is increasing. Usage will in- 

 crease further with the completion 

 of the Lake Wallisville and other 

 reservoirs . 



The Trinity-San Jacinto (Gal- 

 veston) estuary receives most of the 



Lavaca-Tres Palacio (Matagorda) 



The Lavaca-Tres Palacios (Mata- 

 gorda) estuary, constituting about a 

 fifth of the estuarine area in Texas, 

 has a total median annual freshwater 

 inflow of just 1.6 times the estu- 

 arine volume per year. Even though 

 this estuary has over 70 percent of 

 the area of the Trinity-San Jacinto 



415 



