low temperatures, both bottom, and surface, were generally higher at the north- 

 west and southeast margins of the study area, and cooler in a central belt run- 

 ning from the mouth of Trinity River to a point midway between Smith and 

 Houston Points. 



Approximately 60 species of vertebrates were taken throughout the 

 course of the study, and these were dominated by such typical estuarine forms 

 as the Atlantic croaker, Micropogon undulatus, and the bay anchovy, Anchoa 

 mitchilli. (See figure. ) The fresh-water catfishes, Ictalurus punctatus, and 

 I. furcatus, were found near the center of the bay during February and March 



19 eT 



BAY ANCHOVY 



ATLANTIC CROAKER - 



LAR6ESCALE MENHADEN 



SAND SEATROUT 



RIVER SHRIMP 



BROWN SHRIMP 



WHITE SHRIMP 



BLUE CRAB 



-1 — I — I — I — I — I — I — I — I — I I I I r 



FEB MAMJJASONDJFM APR 

 1961 1962 



Months of greatest relative seasonal occurrence 

 of principa.1 fish and shellfish. 



The fresh-water shrimp, Macrobrachium ohione, and the blue crab 

 dominate the motile invertebrate fauna during the early spring but are grad- 

 ually replaced in late spring by the brown shrimp. This species is in turn re- 

 placed by the white shrimp in midsummer (August). 



From the above data coupled with those found in the literature, it 

 appears that optimum salinity for the Trinity Bay estuarine habitat lies be- 

 tween 10%o and 17%o with the lower and higher extremes appearing near to and 

 away from the mouth of the river, respectively. To maintain this habitat, it 

 was recommended that a mean monthly discharge of 2, 000 c.f. s. be main- 

 tained during the critical months of March through October when the bays are 

 utilized by important estuarine species. 



69 



