Monthly Temperature and Salinity Measurements 



of Continental Shelf Waters of the 



Northwestern Gulf of Mexico, 1963-65^ 



ROBERT F. TEMPLE,- DAVID L. HARRINGTON, ' and JOHN A. MARTIN- 

 ABSTRACT 



Temperature and salinity observations made monthly from January 1963 to December 1965 at 48 

 stations in the northwestern Gulf of Mexico are presented. Off the coasts of Louisiana and Texas 

 monthly average temperatures of surface and bottom waters at station depths of 7, 14, 28, 46, and 73 m 

 exhibited seasonal trends that were similar over a 3-yT period. Monthly average temperatures of sur- 

 face and bottom waters were generally similar at station depths of 7 and 14 m, but differences were 

 noted at station depths of 28, 46, and 73 m and increased with depth. Maximum average temperatures 

 of bottom waters at station depths generally greater than 14 m occurred after surface temperatures 

 had passed their maximum and were dropping. 



Salinities of surface and bottom waters varied markedly at 7- and 14-m stations, whereas at 

 deeper stations seasonal fluctuations were restricted primarily to surface waters. The magnitude of 

 yearly salinity fluctuations decreased with an increase in distance offshore. The effects of the seasonal 

 freshwater inflow of the Mississippi River and other Louisiana rivers on salinities were clearly ap- 

 parent in Louisiana and Texas offshore waters, although in the latter case there may have been a I- or 

 2-mo lag. 



INTRODUCTION 



Between 1962 and 1965 the Galveston Laboratory of 

 the National Marine Fisheries Service, formerly the 

 Bureau of Commercial Fisheries, conducted an inten- 

 sive survey of the waters over the continental shelf of the 

 northwestern Gulf of Mexico. This survey was designed 

 primarily to provide biological information on shrimp 

 (Kutkuhn 1963; Temple and Fischer 1965 and 1967; 

 Brusher et al. 1972; and Temple 1973) and finfish (Moore 

 et al. 1970), but hydrographic data also were collected 

 during the study to provide information essential for a 

 more complete understanding of the environment over 

 the continental shelf. 



Hydrographic studies have been conducted periodical- 

 ly throughout the offshore waters of the Gulf of Mexico 

 over the past 35 yr, but these studies generally have been 

 either 1) extensive efforts covering large geographical 

 areas of the Gulf on a seasonal or sporadic basis, or, 2) in- 

 tensive efforts investigating specific phenomena over a 

 restricted geographical area. Studies in the first category 

 include those reported by Collier 1958; Ichiye 1962; Arm- 

 strong and Grady 1967 and 1968; and Nowlin and McLel- 

 lan 1967. Those in the second category include inves- 

 tigations reported by Gunter 1945; Marvin 1955; Drum- 



The compilation and tabulation of part of the data reported herein 

 were supported under the Department of Interior's Bureau of Land Man- 

 agement Interagency Agreement #08.550-lA5-19. 



Gulf Coastal Fisheries Center. National Marine Fisheries Service, 

 NOAA. 4700 Avenue U, Galveston, TX 77550. 



Marine Resources Extension Service, P.O. Box 517, Brunswick, GA 

 31520. 



mond and Austin 1958; Curl 1959; Finucane and 

 Dragovich 1959; Wennekens 1959; Dragovich 1961 and 

 1963; Dragovich et al. 1961 and 1963; Jones et al. 1965; 

 Stevenson and Leipper 1967; Armstrong 1967 and 1969; 

 Armstrong et al. 1967; and Nowlin and Parker 1974. 

 Additional general information is provided by Fuglister 

 1947; Leipper 1954; and U.S. Naval Oceanographic 

 Office 1972. 



The temperature and salinity information presented in 

 this report adds to the hydrographic data base for the 

 Gulf of Mexico, and is unique in several respects. First, 

 measurements were made generally on a monthly basis 

 at specified locations in the northwestern Gulf of Mexico 

 over a 3-yr period, thus providing a time series heretofore 

 unavailable. Second, these measurements were 

 restricted to a portion of the U.S. continental shelf that is 

 noted for its valuable shrimp and mineral resources 

 which must receive adequate consideration in extended 

 jurisdiction and coastal zone management. 



PROCEDURES 



Between January 1963 and December 1965, 35 cruises 

 were conducted in continental shelf waters with the 27-m 

 chartered shrimp trawler MV Gus III. Observations were 

 made monthly at stations positioned on eight transects 

 located west of the mouth of the Mississippi River and 

 extending to just north of the Mexico-U.S. border (Fig. 

 1). Stations on two additional transects east of the 

 Mississippi River were occupied only in 1963 during 

 every other month beginning in February. Along each 

 transect stations were positioned in predetermined total 



