'.-^^ •/ 



'^7r^'Ww^WW^:mS 



Figure 18. — Simulating a natural environment with an artificial synthetic fibrous material. 



model testing to obtain information on the rate 

 and pattern of pollution dispersion. 



Updating and analysis of historical fishery 

 harvest data of the Galveston estuary are 

 continuing. These data will be used for project- 

 ing influences on fishery resources caused by 

 the proposed plan for hurricane protection. 



Richard J. Hoogland, Project Leader 



ECOLOGY OF WESTERN GULF ESTUARIES 



During the year we studied the hydrography 

 of Galveston Bay, emigration of brown and 

 white shrimp, and methods for identifying 

 postlarval penaeid shrimp. 



Hydrology 



During 1966, temperature and salinity meas- 

 urements were made monthly, or sometimes 

 more frequently, at selected locations (fig. 2.Q) 

 in Galveston Bay. Although temperature and 

 salinity values varied between areas within 

 the bay during any one cruise, all data were 

 connbined and averaged by cruise to depict 

 generally seasonal trends for the entire bay 

 (fig. 21). Also included are river discharge data 

 from the Trinity and San Jacinto Rivers, the 

 two largest sources of fresh water flowing into 

 Galveston Bay. 



Average bottom water temperatures in the 

 bay varied from 11.0° C. (51.8° F.) in Decem- 

 ber to 30.5° C. (86.9° F.) in July. The highest 

 temperature, 36° C. (96.8° F.) was recorded 

 in June, and the lowest, 5.0° C. (41.0° F.), in 

 February and December. Usually, fluctuation 

 in temperature throughout the bay on a partic- 

 ular date (indicated by the range in figure Zl) 

 was greatest from November to March. 



Stream-flow records for the Trinity and 

 San Jacinto Rivers indicate a large volume of 

 stream discharge in May. It is apparent that 

 this flow of fresh water affected bottom 

 salinities throughout the bay. Average bottom 

 salinities were reduced to 1 p.p.t. (part per 

 thousand) in Trinity Bay and below 10 p.p.t. in 

 lower Galveston and East Bays. Recovery of 

 salinities to levels that existed before the high 

 discharge required about 4 months in Trinity 

 Bay. 



The importance of water temperature in 

 controlling the growth of brown shrimp and 

 causing juvenile white shrimp to start emi- 

 grating from bays has been clearly demon- 

 strated. Therefore, we are analyzing our data 

 on temperature and shrimp catch per unit of 

 effort in Galveston Bay to determine if water 

 temperature can be used to predict the time 

 that (1) brown shrimp first become available 

 to the bait fishery and (2) white shrimp emigrate 

 from the bay. 



23 



