FISHERY BULLETIN: VOL. 74, NO. 1 



Table 3. — Comparisons of catches between areas (bay; bay- 

 ward canal, BC; marsh; upland canal, UC) by species and time 

 of day (Tukey's w-procedure with 60 df). 



Species and 

 time of day 



Area, mean catch ( ), and significance lines' 



Brown shrimp: 

 Day 



Night 



White shrimp: 

 Day 



Night 



Grass shrimp: 

 Day 



Night 



Blue crabs: 

 Day 



Night 



Pink shrimp: 

 Day 



Night 



Bay 



(81.4) 



UC 



(99.7) 



Marsh 

 (163.4) 



BC 



(260.5) 



UC 



(1.2) 



Bay 

 (2.4) 



BC 



(11.2) 



Marsh 

 (12.5) 



UC 



(0.1) 



BC 



(0.3) 



Bay 

 (1.0) 



Marsh 

 (2.0) 



UC 



(1.5) 



BC 

 (2.2) 



Bay 

 (2.8) 



Marsh 

 (7.9) 



'Any two means not underscored by the same line are significantly different 

 at the 5% level. 



marsh. In contrast, mean oxygen values observed 

 in the upland canal area remained below 3.0 ml/ 

 liter from 20 May to 12 August and were below 

 2.0 ml/liter on three occasions. From 20 May to 12 

 August, about 24% of the individual observations 

 of oxygen values from the upland canal stations 

 were below 1.0 ml/liter, whereas all individual 

 observations from the other three areas were 

 above 1.5 ml/liter. 



The normal patterns of seasonal abundance 

 were reflected for brown shrimp, white shrimp, 

 and blue crabs by catches in the bayward canal, 

 marsh, and bay areas (Figure 2). Immigration 

 and emigration in Galveston Bay by brown and 

 white shrimps occur during different seasons 

 (Baxter and Renfro 1966; Trent 1967; Pullen and 

 Trent 1969). Brown shrimp postlarvae immigrate 

 in late winter and early spring and most of the 

 juveniles emigrate in late spring and early sum- 

 mer. White shrimp postlarvae immigrate in the 

 summer, and the juveniles emigrate in the fall or 

 early winter depending on water temperature. 

 Blue crabs are abundant throughout the year in 

 Galveston Bay (Chapman 1965). 



N. 3 



E 





BROWN SHRIMP 



20 



■*'''''"'"~'>^f,,„X«t""""*'''''i^ 



PINK SHRIMP 



^Hfe»«,, „.„ ,„„ 



25 8 22 6 20 3 17 I IS 29 12 26 9 23 7 21 

 MAR APR MAY JUNE JULY AUG SEPT OCT 



Figure 2. — Mean dissolved oxygen values, and mean catch of 

 each species by area and time of year. 



Patterns of seasonal abundance for grass and 

 pink shrimps are not documented for the Galves- 

 ton Bay system. In Redfish Bay, Tex. (about 150 

 miles southwest of our study area), Hoese and 



198 



