RENAUD: HYPOXIA IN LOUISIANA WATERS 



90°47'W to 93°02'W was sampled with a 24.4 m 

 steel-hull commercial shrimp trawler from 30 June 

 to 6 July 1983 (Fig. 1). Depth varied from 4 to 20 

 m and distance from shore ranged from 8 to 54 km. 

 Shrimp and bottomfish were collected at 34 of 65 

 stations in 20-min tows with a 12.2 m semiballoon 

 trawl. The same trawl was used as a midwater 

 shrimp sampler above previously identified hypoxic 

 water. Surface and bottom measurements of water 

 temperature, salinity, and dissolved oxygen concen- 

 tration were recorded before each tow. Water 

 samples were collected with a Kemmerer bottle 

 Salinities were measured with a refractometer. 

 Temperature and dissolved oxygen concentration 

 were measured with a YSI Model 51-B. Surface and 

 bottom hydrographic data were collected at the re- 

 maining 31 stations. The Southeast Area Monitor- 

 ing and Assessment Program (SEAMAP) 3 person- 

 nel collected similar data off Louisiana in June 1983. 

 SEAMAP dissolved oxygen data were included in 

 the contour analyses. 



The Harvard SYMAP program (Dougenik and 

 Sheehan 1975), a Northwest Alaska Fisheries Center 

 Contour Subroutine, and the Galveston Laboratory 

 Generalized Mapping system were utilized to pro- 

 duce a map of dissolved oxygen contours off Loui- 

 siana. Koi 4 presents an indepth explanation of these 

 contour mapping programs. Vertical density gra- 

 dient of the water column, shrimp catch, and fish 

 catch were regressed with bottom water dissolved 

 oxygen concentration. A "best fit" line through the 

 data was determined using the least squares concept. 



Surface water temperature (°C) and chlorophyll 

 content (mg/m 3 ) were measured off Louisiana by 

 the Coastal Zone Color Scanner (CZCS) aboard the 

 Nimbus-7 satellite Personnel from the Mississippi 

 Laboratories of the Southeast Fisheries Center, 

 working at the National Space Technology Labora- 

 tories, Mississippi, used CZCS and "ground truth" 

 field data to predict potentially hypoxic areas in 

 coastal Louisiana waters. 



RESULTS AND DISCUSSION 



Regions of hypoxic bottom water have been 

 detected along portions of the Texas-Louisiana 

 coastline every summer from 1972 to 1983 (Harris 



3 Southeast Area Monitoring and Assessment Program: a State- 

 Federal cooperative research effort organized to assess the distribu- 

 tion and abundance of shrimp and bottomfish in the Gulf of Mexico. 



4 Koi, D. 1985. Generalized geographic mapping system. Un- 

 publ. manuscr., 47 p. Southeast Fisheries Center Galveston 

 Laboratory, National Marine Fisheries Service, NOAA, 4700 

 Avenue U, Galveston, TX 77550. 



et al. 1976; Ragan et al. 1978; Bedinger et al. 1981; 

 Harper et al. 1981; Reitsema et al. 1982; Boesch 

 1983). Hypoxia was noted from 16 June to 6 July 

 1983. It was patchy in distribution and found main- 

 ly in 9 to 15 m depths from south of Barataria Pass 

 to south and west of Marsh Island (Fig. 1). 



A total of 34 fish and 11 invertebrate species were 

 collected offshore The Atlantic croaker, Micropo- 

 gonius undulatus, and the Atlantic threadfin, Poly- 

 dactylies octonemus, were the dominant bottomfish 

 at 58% and 30% of the stations, respectively; Atlantic 

 bumper, Chloroscombrus chrysurus, was the com- 

 mon pelagic. Brown shrimp, Penaeus aztecus; white 

 shrimp, P. setiferus; mantis shrimp, Squilla empusa; 

 and broken-back shrimp, Trachypenaeus sp., were the 

 most common invertebrates collected, but in small 

 quantities. Total crustacean catch was always <5.0 

 kg/h. 



Bottom water dissolved oxygen concentration was 

 significantly correlated with 1) fish biomass (r = 

 0.56, P < 0.001) (Fig. 2) and the number of brown 

 and white shrimp present (r = 0.56, P < 0.002) (Fig. 

 3). Shrimp and bottomfish were generally absent 

 from hypoxic stations. Atlantic croaker were not at 

 stations with hypoxic bottomwater, and shrimp 

 catches never exceeded 2 kg/h in the areas. Sea cat- 

 fish, Arisus felis; butterfish, Peprilus paru; and 

 Atlantic bumper were common in trawls at hypoxic 

 sites. These were also the most abundant fish in mid- 



4.0r- 



x 



Ul 



2 

 i 



CM 



25 2.o 



< 



2 



o 



m 



x 

 to 



o 

 o 



• " • 



y= a + bLogx 

 r=0.56 



0.0 



J. 



I 



_L 



_L 



_L 



2.0 4.0 



BOTTOM WATER DISSOLVED OXYGEN 



CONCENTRATION (PPM) 



6.0 



FIGURE 2— Offshore fish biomass in relation to bottom water 

 dissolved oxygen concentration. 



21 



