Wibbels, Thane, David W. Owens, Colin J. Limpus*, 



and Max S. Amoss 



Field Testing of a Sexinq Technique for Immature Sea Turtles 



Biology Department 

 Texas A&M University 

 College Station, Texas 77843 USA 



♦Queensland National Parks and Wildlife Service 

 Pallarenda Townsville, Queensland 4810, Australia 



Past research indicates that sea turtles possess an 

 environment-dependent sex determination system. As such, sea 

 turtle population sex ratios are of conservation and evolutionary 

 interest. The sex ratio within a population may possibly vary 

 between size classes of turtles due to such factors as seasonal 

 and yearly variations in hatchling production, sex-specific 

 mortality, etc. Therefore, sex ratios should be examined in the 

 various size classes within a population. We hypothesize that an 

 effective initial step is to examine the sex ratio in the post 

 "lost-year"-through-pubescent portion of the population. This 

 portion of the population represents the condensation of many 

 years of hatchling production. Therefore a study of its sex 

 ratio may be free from some of the logistical problems associated 

 with the study of hatchling and adult sex ratios. However, a 

 prerequisite for studying the post "lost-year" -through-pubescent 

 portion of the population is the development of an accurate 

 sexing technique. We have recently completed a field evaluation 

 of a serum testosterone sexing technique for sea turtles. 



Our initial study was conducted in the Cape Canaveral ship 

 channel in collaboration with the National Marine Fisheries 

 Service. During that study, loggerhead turtles were captured by 

 trawling. We collected blood samples from large numbers of 

 turtles via their bilateral cervical sinus. This blood sampling 

 technique is quick, nonharmful, and easily learned. We also 

 laparoscopically examined 21 of those turtles (sex ratio = 

 2.5F:1.0M). This surgical technique facilitates the direct 

 viewing of the gonad and thus a means of positively sexing 

 individual turtles. However, this technique requires surgical 

 training and is logistically difficult to perform in the field. 

 The serum testosterone titers of the male turtles were all 

 greater than those of the females. 



We further evaluated this sexing technique during a six 

 month field project on Heron Atoll in collaboration with the Sea 

 Turtle Research Group of the Queensland National Parks and 

 Wildlife Service. Heron Atoll is located on the southern end of 

 Australia's Great Barrier Reef and it harbors populations of 

 green, loggerhead, and hawksbill turtles. The clear, shallow, and 

 calm waters of the atoll facilitated the use of a "turtle rodeo" 



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