DISTRIBUTION OF BROWN SHRIMP (Penaeus aztecus aztecus IVES) AS 

 RELATED TO TURBID WATER PHOTOGRAPHED FROM SPACE' 



BY MILTON J. LINDNER, Fishery Biologist, AND JAMES S. BAILEY, = Research Oceanographer 



BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 

 GALVESTON, TEXAS 77550 



ABSTRACT 

 Visual evidence of probable relief currents in the Shelf off the Texas Coast, a comparison of the prsition 

 northwestern Gulf of Mexico is provided for the first of relief currents to areas of high shrimp production 

 time by photographs taken from Gemini spacecraft. indicates that photography f.om space can be a valuable 

 After rectification of photographs of the Continental tool for fishery research. 



Oceanographers long ha^e predicted the exist- 

 ence of relief or rip currents between Galveston 

 and Corpus Christi, Tex. (Sweitzer, 1898; Smith, 

 Medina, and Abella, 1951; Curray, 1960), and 

 navigators have called the area the "Whirlpool of 

 the Gulf" (U.S. Coast and Geodetic Survey, 1949) . 

 The offshore relief currents result from the con- 

 vergence of southerly and northerly currents, 

 which causes a piling up of water that is relieved 

 by an offshore flow. The buildup and eventual 

 release of waters in the Galveston-Corpus Christi 

 area are continuously recurring sequences of events 

 related to the total Gulf system. 



Visual evidence of count ercun-ents, which have 

 never befoi-e been documented by oceanographic 

 techniques, is apparently provided by figure 1. This 

 figure is a reproduction of a color photograph 

 taken by XASA (National Aeronautics and Space 

 Administration) from an altitude of 330 km. on 

 November 14, 1966. In addition to showing the dis- 

 tribution of suspended material in bay and Gulf 

 waters, the discharge patterns from the bays, the 

 major eddy currents, and the relative direction of 

 the currents, we believe it illustrates clearly the 

 long-suspected phenomenon of rip or relief 

 currents. 



Sediments in the water provide the contrast that 

 permits us to see the interaction of the coastal cur- 

 rent systems. Perhaps the most obvious feature is 



the discharge of sediment at the entrances to Lake 

 Charles, La., and Sabine Lake and Galveston Bay, 

 Tex. Large volumes of sediment in these areas are 

 lx>ing carried into the Gulf and innnediately trans- 

 ported southward by an alongshore current. Less 

 noticeable but vastly larger are two areas of dis- 

 colored water south of Galveston that extend east- 

 ward. These plumes of suspended material are 

 aligned by moving water and most likely represent 

 the areas of rip or relief currents predicted by 

 oceanographers. The plumes, outlined in figure 2, 

 are believed to be semijjenrianent features of the 

 Gulf current system, although their locations, in- 

 tensity, and dimensions undoubtedly fluctuate 

 throughout the year. Obviously, they must have 

 some effect on the bottom sediments and nutrient 

 supply. 



Our conclusions admittedly are conjectural be- 

 cause of the lack of necessaiy detailed physical and 

 chemical data from oceanographic and bottom sur- 

 veys made in and aroiuid the areas under con- 

 sideration. A definite relation does exist, however, 

 between the shrimp catch, trawling frequency, and 

 the plumes shown in figure 2. 



Rectification of the Gemini photograph to ONC 

 (Operational Navigation Chart) No. 24 (fig. 3) 

 revealed that the plumes were in BCF (Bureau 

 of Commercial Fisheries) statistical area 19 and 

 the lower portion of area 18 (fig. 4). The best 



' Contribution No. 276, Bureau of Commercial Fisheries Bioloei'^al Laboratory, Galveston, Tex. 77550. 

 ! Present address: TRW Systems, 1 Space Park, Redondo Beach, Calif. 90278. 



Published December 1968. 



FISHERY BULLETIN: VOL. 67, NO. 2 



289 



