Shrimp and redfish studies; Bryan Mound brine disposal site off Freeport, Texas, 1979-1981. Volume III: Shrimp spawning site survey.




Gallaway, B.J.
Reitsema, L.A.

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NTIS; U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Center, Galveston Laboratory


In a study performed over October 1979-September 1980, immature brown shrimp were found to move through the nearshore marine environment in the vicinity of the brine diffuser offshore Freeport, Texas (and in the surrounding area) in two waves during summer as they emigrated from the estuaries to offshore spawning habitats. The major spawning habitat of the brown shrimp is well offshore, generally located along the 40m to 50m depth contours. White shrimp in the study area appeared mainly restricted to a band within about 8 km of the beach and spawning mainly occurred in these nearshore areas. The diffuser appears well-sited in terms of minimizing the impacts on spawning of these two shrimps--it is seaward of the area of greatest white shrimp activity and shoreward of the area of greatest brown shrimp activity. Our data show a marked fall (August, September, October) spawning peak for brown shrimp and suggests that a spring peak may also be characteristic. White shrimp were found to spawn during summer periods, particularly June and July. Penaeid type eggs were seldom encountered in the samples; nauplii (Penaeidae) were abundant in the offshore block from June-September; protozoea (Penaeidae) were found abundant only during August at offshore stations (block A); mysis stage larvae (Penaeus spp.) were more abundant in August than in any other month when they were most abundant in block A; and Penaeus spp. postlarvae were well represented in all sampling areas, being most abundant in August. Results of principal component and cluster analyses clearly separated block A sites from nearshore block B and C sites. Nearshore sites exhibited considerable overlap and no patterns were detected that could be related to white shrimp spawning areas. Results of multiple linear regression analyses showed the number of brown shrimp in spawning condition was greatly correlated with temperature and somewhat with levels of sterols in potential prey organisms. The number of white shrimp in spawning condition was strongly correlated with conductivity (salinity) and with four other variables, including in order of importance after conductivity, concentration of fatty acid 20:5 in the biota, temperature, dissolved oxygen and levels of sterols in the sediments. The discriminant function analysis yielded a function that could discriminate with 100% success between sites in blocks B and C having or not having spawning white shrimp. The variables included in this function in order of their decreasing importance were sediment sterols, total organic carbon, biota carotenoids and mean particle size.


84 p.


shrimp fisheries, penaeid shrimp, Penaeus aztecus, brown shrimp, white shrimp, Penaeus setiferus, spawning, nursery grounds, statistical analysis, salinity, biota, migrations, temperature, oxygen, sediment chemistry, sterols