Our work in assessing water developnnent 

 projects continues to increase and become 

 more complex. The economic potential of 

 fishery resources developed during our pre- 

 liminary evaluation of the Texas Basins Project 

 (U.S. Fish and Wildlife Circular No. 230) now 

 permits us to nnake monetary assessments of 

 many projects that would directly modify or 

 destroy an estuary. We can estimate, for 

 example, the average value per acre of 

 estuarine nursery habitat as well as the value 

 of a unit volume of tributary fresh water. 

 Knowledge of these values is a very useful 

 tool which has already served well in the 

 evaluation of several projects. Research, how- 

 ever, must continue to provide more knowledge 

 so we can improve these interim figures and 

 thus better defend our fishery resources during 

 the struggle to develop the water resources 

 and estuarine basins of the Gulf coast. 



The Galveston estuary usually receives 

 sufficient fresh water to provide a wide range 

 of environmental conditions; consequently, it 



accomnnodates at high levels many different 

 estuary-dependent species. Among them are 

 large numbers of shrimp that contribute 

 significantly to the catch in the Gulf of 

 Mexico. 



Many species, including the white and brown 

 shrimp, travel extensively while undergoing 

 development in the estuary and, so, occupy 

 several different hydrological and hydrographic 

 zones over a relatively short period. Perhaps 

 their requirements or preferences change 

 from one developmental stage to the next. 

 For example, in the Galveston estuary during 

 1963 and 1964 the smaller juvenile brown 

 shrimp were concentrated in those parts of 

 the estuary where salinity was less than 

 10 p.p.t. As they grew, however, they occupied 

 zones of higher salinity. They did not use 

 extensively those portions of the estuary 

 where salinity exceeded 25 p.p.t. We developed 

 this information by measuring more than 

 40,000 shrimp collected in 1,655 trawl sam- 

 ples (fig. 24). 



Figure 24. — Project personnel in our new laboratory facility Identifying and 

 measuring small shrimp collected from Galveston estuary. 



29 



