Sea Turtle Strandings 



and Shrimp Fishing Effort in the 



Northwestern Guif of Mexico, 1 986-89 



Charles W. Caillouet Jr. 



Marcel J. Duronslet 



Galveston Laboratory. Southeast Fisheries Science Center 



National Marine Fisheries Service. NOAA. Galveston, Texas 77551-5997 



Andre M. Landry Jr. 



Department of Marine Biology, Texas A&M University 

 Mitchell Campus, Pelican Island, Galveston, Texas 77553 



Dickie B. Revera 



Galveston Laboratory, Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA, Galveston, Texas 77551-5997 



Donna J. Shaver 



Padre Island National Seashore, National Park Service. U.S. Department of Interior 

 9405 South Padre Island Drive, Corpus Chnsti, Texas 78418 



Kerry M. Stanley 

 Robert W. Heinly 

 Erich K. Stabenau 



Galveston Laboratory, Southeast Fisheries Science Center 



National Marine Fisheries Service, NOAA, Galveston, Texas 77551-5997 



Incidental capture of sea turtles in 

 shrimp trawls is the most important 

 human cause of sea turtle mortality 

 (Magnuson et al. 1990). Offshore 

 stocks of penaeid shrimp were dis- 

 covered in the Gulf of Mexico in the 

 mid-1980s, and expansion of the off- 

 shore shrimp fishery began in the 

 late 1940s following World War II 

 (Whitaker 1973, Krauthamer et al. 

 1984, Tetty and Griffin 1984, Ray- 

 burn 1989). The industry continued 

 to expand and improve its fishing 

 technology into the 1980s. During 

 the same period when shrimping 

 effort was increasing and harvest- 

 ing technology was improving, the 

 abundance of sea turtles declined 

 (Magnuson et al. 1990). 



Sea turtle strandings along 

 coastal shorelines of the southeast- 

 ern United States have been used 

 as one index of mortality due to 

 shrimping (Magnuson et al. 1990). 



An increase in sea turtle strandings 

 during commercial penaeid shrimp 

 fishing seasons and a decrease with 

 the closing of these seasons have 

 been observed on the Atlantic coast 

 of the southeastern United States 

 (Hillestad et al. 1978, Talbert et al. 

 1980, Ruckdeschel and Zug 1982, 

 Booker and Ehrhart 1989, Schro- 

 eder and Maley 1989). The relation- 

 ship between sea turtle strandings 

 and shrimp fishing in the north- 

 western Gulf of Mexico has received 

 less attention (Rabalais and Raba- 

 lais 1980, Amos 1989, Whistler 1989, 

 Magnuson et al. 1990), although 

 Texas and Louisiana together pro- 

 duce most (almost 74% during 

 1986-89) of the offshore (seaward 

 of barrier islands) commercial catch 

 of penaeid shrimp in the southeast- 

 ern United States. In this study, we 

 used product-moment correlation 

 analysis to test the null hypothesis 



that there was no relationship be- 

 tween monthly sea turtle strand- 

 ings and shrimp fishing effort in the 

 northwestern Gulf of Mexico coast 

 during 1986-89. 



Sea turtles would not be captured 

 in shrimp trawls if the temporal- 

 spatial distributions of sea turtles 

 and shrimp fishing effort did not 

 overlap to some extent. However, 

 we have no a priori reason to expect 

 that temporal-spatial distributions 

 of sea turtles and shrimp fishing ef- 

 fort match exactly. Shrimp trawling 

 in the northwestern Gulf varies sea- 

 sonally and spatially as related to 

 the annual cycle of occurrence and 

 abundance of short-lived penaeid 

 shrimp (Kutkuhn 1962, Neal and 

 Maris 1985). It is most intense 

 during spring and summer when 

 surface waters are warm. Shrimp 

 spawn in the Gulf where the eggs 

 hatch and larvae develop as they are 

 carried toward the estuaries in 

 spring and early summer. As post- 

 larvae, shrimp enter the estuarine 

 nursery areas where they grow for 

 several months before emigrating 

 to the Gulf and becoming vulnerable 

 to the offshore shrimp fishery. There 

 they continue to grow and migrate 

 to deeper waters to spawn while be- 

 ing exploited by the fishery. In con- 

 trast, sea turtles are long-lived and 

 can be exposed to mortality risks 

 for decades. Based on strandings, 

 commercial and recreational fishing 

 bycatch, and aerial surveys, sea 

 turtles are most abundant in the 

 northwestern Gulf during spring or 

 early summer, with a lesser peak in 

 abundance in autumn (Hildebrand 

 1982, Fritts et al. 1983, Thompson 

 1988, Magnuson et al. 1990). 

 Waters of the northwestern Gulf 

 are foraging habitat for the turtles, 

 and they are used as migratory 

 routes when the turtles move north- 

 ward in spring and southward in 

 autumn (Hildebrand 1982, 1983). 

 The most numerous species in the 



Manuscript accepted 23 August 1991. 

 Fishery Bulletin, U.S. 89:712-718 (1991). 



712 



