Critical Approaches to Sex Determination in Sea Turtles
117
sex ratios of hatchling vs. immature loggerheads in U.S. waters is intriguing and
worthy of future studies.
A similar scenario may occur with the Kemp’s ridley sea turtle. Data suggest a
strong female-bias (possibly 80–90% female or greater) of hatchling sex ratios produced over 4 recent years, 76 and this could be indicative of previous years because
almost all nests have been translocated to the same protected egg “corral” for more
than 20 years. Blood testosterone levels were used to predict the sex of 39 immature
Kemp’s ridley turtles captured along the Gulf coast of Florida and predicted a 1.7:1.0
(female–male) sex ratio. 77 A similar study examined blood testosterone in 42 Kemp’s
ridley turtles captured along the Gulf coast of Florida and reported a sex ratio of
approximately 3.7:1 (female–male). 78 Laparoscopy was used to sex 231 Kemp’s ridley
turtles captured off the coast of Texas and Louisiana, and found a sex ratio of 1.3:1
(female–male). 79 Necropsy was used to sex 89 stranded Kemp’s ridley turtles from
the Texas coast, and found a sex ratio of 3:1 (female–male). 80 A similar study examined
89 stranded immature Kemp’s ridleys from the Texas coast and found an approximate
2.0:1.0 (female–male) sex ratio. 68B Thus, the sex ratios reported for the juvenile portion
of this population appear female-biased, but the bias is distinctly less than that predicted
for recent hatchling sex ratios. As with the loggerhead sex ratios described above, the
discrepancy between the sex ratios of hatchling vs. immature ridley turtles is worthy
of future studies.
Although female-biased sex ratios have been reported in many populations, a
near 1:1 sex ratio has been predicted for the immature portion of the Hawaiian green
turtle population on the basis of two different studies. One study used blood testosterone levels to sex 63 juvenile turtles captured in waters off the coasts of Molokai
and Hawaii, and predicted a sex ratio of approximately 1:1. 81 A second study used
necropsy to examine 421 immature and adult turtles, and the sex ratio of juveniles
did not significantly differ from a 1:1 sex ratio. 82 The Hawaiian green turtle represents
an interesting population for sex ratio studies because it is an isolated group of green
turtles, 83 and data suggest relatively cool incubation temperatures in comparison to
those of other green turtle populations. 84 It is possible that this population represents
an excellent example of how the thermal environment of a nesting beach may select
for a specific pivotal temperature.
Blood testosterone levels were also used to predict the sex of 111 immature
green turtles from Bermuda. 85 The results indicated a 1.4:1.0 (female–male) sex
ratio, which did not significantly differ from a 1:1 ratio. Genetic data from that group
of turtles suggest that the majority originated from Caribbean nesting beaches,
particularly Tortuguero, Costa Rica. 86 A previous study at Tortuguero predicted an
approximate 2:1 (female–male) hatchling sex ratio, 47 but a more recent study suggested a male-biased (2:3, female–male) hatchling sex ratio from Tortuguero. 87
Compared to the loggerhead and Kemp’s ridley data reviewed above, these represent
a relatively small difference between predicted hatchling and immature sex ratios;
each study involved only a single nesting season and may not be indicative of all
nesting seasons at Tortuguero. Nevertheless, this is another example of possible
variation of sex ratios within a population.
Chaloupka and Limpus 63 conducted a comprehensive examination of sex ratios
within the immature and adult portions of green and loggerhead turtles inhabiting the
1123 book.book Page 117 Monday, November 11, 2002 11:11 AM
117
sex ratios of hatchling vs. immature loggerheads in U.S. waters is intriguing and
worthy of future studies.
A similar scenario may occur with the Kemp’s ridley sea turtle. Data suggest a
strong female-bias (possibly 80–90% female or greater) of hatchling sex ratios produced over 4 recent years, 76 and this could be indicative of previous years because
almost all nests have been translocated to the same protected egg “corral” for more
than 20 years. Blood testosterone levels were used to predict the sex of 39 immature
Kemp’s ridley turtles captured along the Gulf coast of Florida and predicted a 1.7:1.0
(female–male) sex ratio. 77 A similar study examined blood testosterone in 42 Kemp’s
ridley turtles captured along the Gulf coast of Florida and reported a sex ratio of
approximately 3.7:1 (female–male). 78 Laparoscopy was used to sex 231 Kemp’s ridley
turtles captured off the coast of Texas and Louisiana, and found a sex ratio of 1.3:1
(female–male). 79 Necropsy was used to sex 89 stranded Kemp’s ridley turtles from
the Texas coast, and found a sex ratio of 3:1 (female–male). 80 A similar study examined
89 stranded immature Kemp’s ridleys from the Texas coast and found an approximate
2.0:1.0 (female–male) sex ratio. 68B Thus, the sex ratios reported for the juvenile portion
of this population appear female-biased, but the bias is distinctly less than that predicted
for recent hatchling sex ratios. As with the loggerhead sex ratios described above, the
discrepancy between the sex ratios of hatchling vs. immature ridley turtles is worthy
of future studies.
Although female-biased sex ratios have been reported in many populations, a
near 1:1 sex ratio has been predicted for the immature portion of the Hawaiian green
turtle population on the basis of two different studies. One study used blood testosterone levels to sex 63 juvenile turtles captured in waters off the coasts of Molokai
and Hawaii, and predicted a sex ratio of approximately 1:1. 81 A second study used
necropsy to examine 421 immature and adult turtles, and the sex ratio of juveniles
did not significantly differ from a 1:1 sex ratio. 82 The Hawaiian green turtle represents
an interesting population for sex ratio studies because it is an isolated group of green
turtles, 83 and data suggest relatively cool incubation temperatures in comparison to
those of other green turtle populations. 84 It is possible that this population represents
an excellent example of how the thermal environment of a nesting beach may select
for a specific pivotal temperature.
Blood testosterone levels were also used to predict the sex of 111 immature
green turtles from Bermuda. 85 The results indicated a 1.4:1.0 (female–male) sex
ratio, which did not significantly differ from a 1:1 ratio. Genetic data from that group
of turtles suggest that the majority originated from Caribbean nesting beaches,
particularly Tortuguero, Costa Rica. 86 A previous study at Tortuguero predicted an
approximate 2:1 (female–male) hatchling sex ratio, 47 but a more recent study suggested a male-biased (2:3, female–male) hatchling sex ratio from Tortuguero. 87
Compared to the loggerhead and Kemp’s ridley data reviewed above, these represent
a relatively small difference between predicted hatchling and immature sex ratios;
each study involved only a single nesting season and may not be indicative of all
nesting seasons at Tortuguero. Nevertheless, this is another example of possible
variation of sex ratios within a population.
Chaloupka and Limpus 63 conducted a comprehensive examination of sex ratios
within the immature and adult portions of green and loggerhead turtles inhabiting the
1123 book.book Page 117 Monday, November 11, 2002 11:11 AM