commercial shrimp fishery. These 

 are Penaeus aztecus Ives, the brown 

 shrimp, Penaeus setiferus Linnaeus, 

 the white shrimp, and Penaeus duor- 

 arum Burkenroad, the pink shrimp in 

 the Gulf of Mexico (Van Lopik et al. 

 1980). Adult brown shrimp and, in 

 some cases, white shrimp are caught 

 by the offshore operators while ju- 

 venile brown shrimp and white shrimp 

 are caught by the inshore shrimpers. 



The annual catches of these 

 dominant species tend often to be 

 highly variable, associated to a 

 great degree with environmental con- 

 ditions. The effects of the environ- 

 mental factors on the brown, white 

 and pink shrimp are most pronounced 

 during their critical estuarine- 

 growth phase (Van Lopik et al. 1980). 



RELATIONSHIP OF THE SHRIMP INDUSTRY 

 TO FRESHWATER INFLOWS 



To understand the importance of 

 freshwater inflows and the resulting 

 marsh area vitality to the shrimp 

 industry, it is necessary to review 

 the life cycle of the commercial 

 penaeid shrimp. Current thought is 

 that these shrimp spawn offshore in 

 the Gulf of Mexico. The eggs hatch 

 into the first of three larval 

 stages. For 15 to 20 days, the 

 shrimp larvae drift helplessly with 

 the prevailing currents, hopefully 

 terminating their journey at the en- 

 trance to a bay system. The larval 

 shrimp then molt into postlarvae 

 and begin another migration to the 

 upper bays and estuarine areas. 

 With favorable conditions, the ju- 

 venile shrimp grow rapidly in these 

 areas. As the shrimp near maturity 

 they begin to migrate through the 



bays and reenter the Gulf. Here 

 spawning takes place and the cycle 

 is reinitiated. 



According to Van Lopik et al. 

 (1980), the weakest link in this cy- 

 cle is the estuarine-growth phase. 

 In this area, local fluctuations in 

 temperature and salinity could po- 

 tentially drastically effect both the 

 availability of marsh suitable for 

 growth and the actual growth rate of 

 the shrimp. In addition, man-made al- 

 terations such as impoundments , bulk- 

 heading and alterations in freshwater 

 discharges can accentuate the fluc- 

 tuations causing considerably more 

 detrimental impact. 



Turner (1977) has observed 

 that there is a direct relationship 

 between actual marsh acreage and 

 yield of shrimp. This work is in 

 harmony with that of Barrett and 

 Gillespie (1973) which shows that 

 the annual brown shrimp production 

 in Louisiana is correlated with the 

 acreage of marsh having waters above 

 10 ppt salinity. 



It appears from these findings 

 that yields of the three major com- 

 mercial species of shrimp in the 

 Gulf of Mexico are dependent on 

 maintenance of healthy estuarine 

 marshes, mangrove areas and grass- 

 beds in their natural state. Speci- 

 fically, these areas provide post- 

 larval, juvenile and subadult shrimp 

 with food and protection from preda- 

 tors as well as assist in main- 

 tenance of the essential gradient 

 between fresh and salt water (Van 

 Lopik et al. 1980). 



A key element to the vitality 

 of a marsh or estuary is in its very 

 definition which speaks to the need 

 for fresh water (Chapman 1972). This 

 mixing of river waters and seawater 



432 



