STUDIES OF POST LARVAL SHRIMP IN 

 VERMILION BAY, LA. 



The University of Southwestern Louisiana 

 has conducted sampling to investigate fluctua- 

 tions in the seasonal abundance of postlarval 

 shrimp in Vermilion Bay since February 1963. 

 Samples are collected each week with a hand- 

 drawn beam trawl that is towed over a meas- 

 ured distance near the shoreline. Three sam- 

 pling stations are located within the bay, and 

 two others are near an entrance to the bay. 

 Results obtained thus far indicate that the 

 movements of postlarval brown and white 

 shrimp into Vermilion Bay take place at 

 about the same calendar time as in the Gal- 

 veston Bay area. Brown shrimp postlarvae 

 predominate in samples taken during the early 

 spring, and postlarval white shrinnp are more 

 abundant beginning in June. The relative num- 

 bers of postlarvae vary considerably among 

 the five stations, and it is apparent that some 

 sampling locations do not provide a reliable 

 indication of postlarval abundance. We antici- 

 pate that a relation can be found between the 

 abundance of postlarvae at one or two stations 

 and the subsequent production of connmercial 

 shrimp. 



We made a special study to determine the 

 causes of fluctuations in the number of post- 

 larvae caught over a short time interval near 

 the entrance to Vermilion Bay from August 30 

 to September 3, 1964. We obtained duplicate 

 samples of postlarvae at 2-hr. intervals 

 throughout the 4-day period. The results of this 



study indicate that the number of postlarvae 

 in a sample is directly related to the tidal 

 stage (fig. 23). This knowledge makes it apparent 

 that future collections from this location should 

 be made at the same stage of the tide each week 

 if they are to reflect the abundance of post- 

 larvae. 



Charles W. Caillouet, Jr., Project Leader 



University of Southwestern Louisiana 

 (Contract No. 14- 17-0002-100) 



NUM6£» OP POSTLflftvaE 



»«00 - 



u\l 



v-^V 



TlOE euEvATlON 



/ XxV 



ofc=Z_ 



\ / 



"^ 



■'~^ 



r-^-- 



\i 



~i r^ 1 1 — — I 1 



"200 2400 t200 2dOO tSOO 2400 tZOO 2400 i200 



AUG 30 AUG 31 SEP i SEP 2 SEP 3 



1964 



Figure 23. --Fluctuations in the catch of postlarval shrimp 

 and in tide elevation near Marsh Island, La., August- 

 September 1964. 



ESTUARINE PROGRAM 



The Gulf of Mexico contributes almost one- 

 third of the total U.S. commercial fishery 

 production. Significantly, the bullc of this har- 

 vest is comprised of species that depend on 

 estuaries. Unfortunately, demands on Gulf 

 coast water resources are rapidly causing 

 alteration of most and destruction of many 

 estuaries. Our program of estuarine research 

 studies these valuable coastal waters so that 

 we may develop a better understanding of 

 the mutual relations of the estuary-dependent 

 animals and their environment. The informa- 

 tion from this research provides the basis 

 to assure that coastal fishery resources re- 

 ceive adequate consideration in plans to de- 

 velop upland water supplies and estuarine 

 basins. 



We had previously reported that we could 

 describe with reasonable accuracy the seasonal 

 patterns of distribution, size composition, and 



relative abundance of many commercially 

 important species in the Galveston estuary. 

 Now we can also describe in considerable 

 detail many of this estuary's hydrographic 

 and hydrological characteristics. Thus, we 

 are assessing the type of zone most suited 

 for each major species (and the zone to which 

 each developmental stage is best adapted) and, 

 in turn, we hope to determine the amount of 

 fresh water required to maintain such zones 

 for the maximum benefit of estuary-dependent 

 fishery resources. 



Even though the salinity zonation is being 

 studied first because of its direct and meas- 

 urable relation with river discharge, we are 

 also, in a similar manner, assessing other 

 factors--such as temperature, depth, bottom 

 sediment types, primary productivity, pollut- 

 ants, nutrient levels, and geographic location. 

 This phase of study is well underway. 



28 



