900 



600 



- 300 



Figure 11. --Monthly indices of abundance for postlarval, juvenile, and adult brown shrimp, 1960-65. 



the spring peaik, and seldom can the second 

 peak be recognized in the fall commercial 

 fishery for brown shrimp. 



It is most likely that brown shrimp post- 

 larvae which arrive early at Galveston En- 

 trance are killed by abrupt drops in tempera- 

 ture during February and March in some 

 years. For this reason, we are cooperating 

 with personnel of the Experimental Biology 

 Program to determine the low temperature 

 which is lethal to postlarval brown shrimp. 

 This knowledge may help us refine our post- 

 larval index by eliminating from consideration 

 those animals killed by low temperature. 



Postlarvae 



Routine sampling for postlarval shrimp at 

 Sabine Pass, Rollover Pass, Galveston En- 

 trance, and Aransas Pass, Tex., continued 

 throughout the year. Weather was relatively 

 mild during the early part of the 1965-66 

 winter, and a few postlarval brown shrimp 

 came into the bays until mid- January when 

 cold weather apparently curtailed immigration. 

 Postlarval brown shrimp were caught again 

 beginning in late February. The peak move- 

 ment of postlarvae into Galveston Bay was 

 between March 10 and April 15. Postlarval 

 white shrimp were first caught at Galveston 

 Entrance on May 27, or almost a month later 

 thcin in preceding years. 



An experiment was made in September to 

 determine whether postlarvae tend to skirt the 

 main current when they move through the tidal 

 pass at Galveston Entrance. Results agreed 

 with those from a similar study done in the 

 spring of 1964, when we learned that the 

 numbers of postlarvae decreased from the 

 shoreline toward the channel. 



Juvenile Shrimp 



We continued our weekly survey of the 

 Galveston Bay bait-shrimp fishery, to meas- 

 ure the relative abundance of juvenile brown 

 and white shrimp each year. The total catch 

 of bait-size shrimp from Galveston Bay in 

 1965 was 446,700 kg. from an estimated 

 22,700 hours trawling effort. The catch-per- 

 hour increased 18 percent over that of 1964. 

 Juvenile brown shrimp remained in Galveston 

 Bay longer and accounted for a higher percent- 

 age of the bait catch than in 1964. Table 4 sum- 

 marizes statistics for the bait fishery for 1965. 



Table 4. 



-Bait shrimp statistics for Galveston 

 Bay, 1965 



15 



