iiiii* - 



Figure 19. — The Galveston Bay model constructed by Corps of Engineers at Vlcksburg, Miss., that will be used to 

 test proposed plans for hurricane protection. (Galveston, Tex., is located at bottom of picture. Note the Houston 

 Ship Channel extending the entire length of the dewatered model and the Texas City Channel extending from the 

 center to the left, upper-central margin.) 



Studies on the Emigration of Brown 

 and White Shrimp 



The use of closed seasons or minimum size 

 limits to protect juvenile stages of commer- 

 cially important species from commercial 

 harvest is a common practice in the United 

 States. Shrimping regulations for Texas coastal 

 waters, for example, dictate a 45-day closed 

 season during late spring and early sumnner 

 to protect juvenile brown shrimp as they 

 emigrate from the bays to offshore Gulf waters. 

 This closure usually begins June 1 but can be 

 adjusted to 15 days before or after June 1. The 

 date of closure depends on the abundance and 

 size of juvenile brown shrimp in the bays 

 within a particular year. 



To select the closure date, Texas Parks and 

 Wildlife Department personnel depend on trawl 

 samples of shrimp (catch per-unit-of-effort 

 data) from the bays to estimate the time at 

 which most of the shrimp are emigrating to 

 the Gulf. Samples are taken from a broad 

 area within each bay and are costly and time- 

 consuming to obtain. Also, there is a lag (the 

 duration of which is unknown) from the time 



that shrimp are abundant in the bays until they 

 become abtindant in near-shore Gulf waters. 



More accurate and less costly information 

 probably can be obtained on the size of shrimp 

 and time of emigration by sampling in tidal 

 passes if adequate sampling techniques are 

 developed. Also, such techniques, when im- 

 proved, will provide methods for estimating 

 the relative (or absolute) contribution by each 

 bay of selected species to the offshore 

 fisheries. 



We began sampling for shrimp at station 

 1 (see fig. 20) in the Galveston tidal pass in 

 May 1966 and continued through January 1967. 

 A 0,6- by 3.0-m. (2- by 10-foot) net was used 

 during the brown shrimp study. For each 

 series of samples, the trawl was towed for 8 

 minutes at the surface and 8 minutes on bottom. 

 During the white shrimp study, 10-minute tows 

 were made with a 1.2- by 3.0-m. (4- by 

 10-foot) net at the surface, at middepth, and 

 on bottom for each series. The objectives of 

 the studies were to determine for juvenile and 

 subadult brown shrimp, or white shrimp, or 

 both: (1) peaks of ennigration, (2) size at which 

 they emigrate, (3) sex ratio, (4) vertical 



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