118
The Biology of Sea Turtles, Vol. II
waters of the southern region of the Great Barrier Reef from 1985 through 1992. Sex
ratios were determined for 954 green turtles and 271 loggerheads using laparoscopy.
In greens, the sex ratio of immatures fluctuated over the 8-year study, but was consistently female biased. This was contrary to the unbiased sex ratio recorded for immature
greens during an earlier study. 88 The yearly fluctuations in these immature sex ratios
could be due to sampling bias, but could also reflect factors such as year-to-year
variability in hatchling sex ratios. The consistent female bias of immature green turtles
recorded over the 8-year study probably reflects an overall female bias of hatchlings
produced from the southern Great Barrier Reef. 89 The adult sex ratio of greens from
that 8-year study fluctuated significantly and was consistently male-biased, but it was
speculated that the male bias could be due to sex-specific migratory patterns of adults,
which could cause a sampling bias. 63 In contrast to the green turtle data, the sex ratios
of both immature and adult loggerheads from that region remained relatively constant
over the 8-year study, and both were significantly male biased. 63 Similarly, in a study
on foraging grounds along the Queensland mainland, immature greens had a femalebiased sex ratio and immature loggerheads had a male-biased sex ratio. 90,91A
In summary, male-biased, female-biased, and unbiased sex ratios have been
reported in the immature portions of sea turtle populations. Data from a long-term
study of green sea turtles suggest that immature sex ratios within a population can
fluctuate over time. 63,88 The sex ratio in the immature portion of the population most
certainly reflects hatchling sex ratios from previous years, but the exact relationship
is not clear because variations between immature and hatchling sex ratios are suggested in some populations. Potential factors such as sex-specific survival rates and
sex-specific behavioral differences could enter into the equation. A thorough understanding of sex ratio dynamics within a population may require long-term evaluation
of hatchling sex ratios coupled with long-term evaluation within various size classes
of immature turtles within a population.
4.3.6 PROBLEMS ENCOUNTERED WHEN ESTIMATING SEX RATIOS IN
A SEA TURTLE POPULATION
A variety of hurdles must be surmounted to accurately predict a sex ratio in a sea
turtle population. First, a basic need exists to accurately verify or predict the sex of
individual turtles. Fortunately, this is not a problem with adult sea turtles because
males develop a large muscular tail during puberty (see photo by Wibbels 91B ).
However, one should be cautious when assigning sex to minimum-sized adults on
the basis of tail length because it is possible to mistake large immature males for
small mature females. 92 The primary problem associated with accurately predicting
adult sex ratios is potential sampling bias due to sex-specific migratory behavior
(specific examples were discussed previously). One might be able to decrease or
avoid sampling bias by sampling on a foraging ground during a nonmigratory time
of year (e.g., several months after nesting season). Regardless, when estimating adult
sex ratios, one should attempt to interpret the results relative to what is known about
the migratory behavior in a given population.
Evaluation of sex ratios in the immature portion of the population avoids the
problem of sex-specific breeding migrations, but a difficulty arises in identifying the
1123 book.book Page 118 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
waters of the southern region of the Great Barrier Reef from 1985 through 1992. Sex
ratios were determined for 954 green turtles and 271 loggerheads using laparoscopy.
In greens, the sex ratio of immatures fluctuated over the 8-year study, but was consistently female biased. This was contrary to the unbiased sex ratio recorded for immature
greens during an earlier study. 88 The yearly fluctuations in these immature sex ratios
could be due to sampling bias, but could also reflect factors such as year-to-year
variability in hatchling sex ratios. The consistent female bias of immature green turtles
recorded over the 8-year study probably reflects an overall female bias of hatchlings
produced from the southern Great Barrier Reef. 89 The adult sex ratio of greens from
that 8-year study fluctuated significantly and was consistently male-biased, but it was
speculated that the male bias could be due to sex-specific migratory patterns of adults,
which could cause a sampling bias. 63 In contrast to the green turtle data, the sex ratios
of both immature and adult loggerheads from that region remained relatively constant
over the 8-year study, and both were significantly male biased. 63 Similarly, in a study
on foraging grounds along the Queensland mainland, immature greens had a femalebiased sex ratio and immature loggerheads had a male-biased sex ratio. 90,91A
In summary, male-biased, female-biased, and unbiased sex ratios have been
reported in the immature portions of sea turtle populations. Data from a long-term
study of green sea turtles suggest that immature sex ratios within a population can
fluctuate over time. 63,88 The sex ratio in the immature portion of the population most
certainly reflects hatchling sex ratios from previous years, but the exact relationship
is not clear because variations between immature and hatchling sex ratios are suggested in some populations. Potential factors such as sex-specific survival rates and
sex-specific behavioral differences could enter into the equation. A thorough understanding of sex ratio dynamics within a population may require long-term evaluation
of hatchling sex ratios coupled with long-term evaluation within various size classes
of immature turtles within a population.
4.3.6 PROBLEMS ENCOUNTERED WHEN ESTIMATING SEX RATIOS IN
A SEA TURTLE POPULATION
A variety of hurdles must be surmounted to accurately predict a sex ratio in a sea
turtle population. First, a basic need exists to accurately verify or predict the sex of
individual turtles. Fortunately, this is not a problem with adult sea turtles because
males develop a large muscular tail during puberty (see photo by Wibbels 91B ).
However, one should be cautious when assigning sex to minimum-sized adults on
the basis of tail length because it is possible to mistake large immature males for
small mature females. 92 The primary problem associated with accurately predicting
adult sex ratios is potential sampling bias due to sex-specific migratory behavior
(specific examples were discussed previously). One might be able to decrease or
avoid sampling bias by sampling on a foraging ground during a nonmigratory time
of year (e.g., several months after nesting season). Regardless, when estimating adult
sex ratios, one should attempt to interpret the results relative to what is known about
the migratory behavior in a given population.
Evaluation of sex ratios in the immature portion of the population avoids the
problem of sex-specific breeding migrations, but a difficulty arises in identifying the
1123 book.book Page 118 Monday, November 11, 2002 11:11 AM