NOTES 



ANALYSIS OF SEA TURTLE CAPTURES 



AND MORTALITIES DURING 



COMMERCIAL SHRIMP TRAWLING 



Five species of sea turtles occur in coastal United 

 States waters of the southern North Atlantic and 

 the Gulf of Mexico and are listed and protected 

 under the Endangered Species Act (1973). These 

 are the Kemp's ridley turtle, Lepidochelys kempi; 

 hawksbill turtle, Eretmochelys imbricata; 

 leatherback turtle, Dermochelys coriacea; green 

 turtle, Chelonia mydas; and loggerhead turtle, 

 Caretto caretta. Each of these species are cap- 

 tured by commercial shrimp trawlers, and these 

 incidental captures have been identified as a 

 source of sea turtle mortalities (Hopkins and 

 Richardson 1984). 



Several prior studies have attempted to quan- 

 tify turtle catch rates and mortalities by trawlers 

 through interviews with vessel captains (Anony- 

 mous 1976,1 19772; Cox and Mauerman 1976; Ra- 

 balais and Rabalais 1980) and through direct ob- 

 servations by observers during commercial 

 shrimp trawling (Hillestad et al. 1978; Ulrich 

 19783; Roithmayr and Henwood 1982^). While 

 these studies provide estimates of capture and 

 mortality rates, more specific information is re- 

 quired to effectively protect the stocks. In particu- 

 lar, managers need to know when and where tur- 

 tle captures occur, which species are impacted, at 

 what depths the majority of captures occur, and 

 how many turtles are captured and killed. 



This report provides a preliminary analysis of 

 existing data collected by fisheries observers dur- 

 ing commercial U.S. shrimp trawling. Data from 

 three National Marine Fisheries Service (NMFS) 

 observer projects were used for analysis of turtle 

 catch per unit effort (CPUE) and mortality rates. 

 A brief description of the projects follow: 



•Anonymous. 1976. Incidental capture of sea turtles by 

 shrimp fishermen in Florida. Prelimmary report of the Flor- 

 ida West Coast Survey, University of Florida Marine Advisory 

 Program, 3 p. 



^Anonymous. 1977. Alabama shrimp fishermen inter- 

 views for 1977-1978. Marine Resources Office, Alabama Coop- 

 erative Extension Service, 1 p. 



3Ulnch, G. F. 1978. Incidental catch of loggerhead turtles 

 by South Carolina commercial fisheries. Report of the Na- 

 tional Marine Fisheries Service, Contract No. 03-7-042-35151, 

 33 p. 



4Roithmayr, C, and T. Henwood. 1982. Incidental catch 

 and mortality report. Final report to Southeast Fisheries Cen- 

 ter. National Marine Fisheries Service, NOAA, 75 Virginia 

 Beach Drive, Miami, FL 33149, 20 p. 



FISHERY BULLETIN: VOL. 85, NO. 4, 1987. 



1) The sea turtle incidental catch and mortality 

 project was instituted to provide information 

 on the incidental capture and associated mor- 

 tality of sea turtles off the southeastern 

 United States. Trained fishery observers were 

 placed aboard commercial shrimp vessels op- 

 erating on the major grounds in the Gulf of 

 Mexico and southern North Atlantic from 

 1979 through 1981. 



2) The goal of the excluder trawl project was to 

 design an apparatus for use with existing 

 shrimping gear which would effectively pre- 

 vent the incidental capture of sea turtles. Ini- 

 tial design and testing of prototype models 

 were conducted during 1977, and field trials 

 were continued through 1984. Fishery observ- 

 ers aboard cooperative and chartered shrimp 

 trawlers began data collection in 1978. Data 

 collection procedures were similar to those of 

 the incidental catch project except that data 

 records were maintained for each net. In this 

 manner, the performance of excluder nets 

 could be compared with that of standard 

 trawls. 



3) The objectives of the shrimp fleet discards proj- 

 ect were to estimate the magnitude and spe- 

 cies composition of incidental fish captures by 

 the Gulf shrimp fleet. Data were collected 

 through contractual arrangements with state 

 agencies from 1973 through 1978. These agen- 

 cies placed observers on commercial vessels to 

 obtain at-sea sampling off their respective 

 coasts. Data records similar to those of the 

 other two projects were completed for each 

 tow. 



In estimating turtle CPUE and mortalities by 

 species, we restricted our analyses to loggerhead, 

 Kemp's ridley, and green turtles. Leatherback 

 and hawksbill turtles were also captured in 

 shrimp trawls, but the infrequency of captures 

 made predictions of CPUE for these species im- 

 precise. In predictions of CPUE for all species 

 combined, these capture records were included. 



Data Analyses 



For estimations of turtle CPUE and mortali- 

 ties, the three observer projects were merged. For 

 each data set, effort (E) was standardized to re- 



813 



