122
The Biology of Sea Turtles, Vol. II
variations, which suggest that multiyear data are critical to understanding sex ratio
dynamics of sea turtle populations. Multiyear studies of sex ratios from a nesting
beach should consistently address spatial and temporal diversity of nests during each
of the nesting seasons to make year-to-year comparisons meaningful.
4.3.8 MANIPULATION OF HATCHLING SEX RATIOS
Because sea turtles possess TSD, it is possible to artificially alter hatchling sex ratios.
However, there has been considerable debate as to whether sex ratio manipulation is an
appropriate conservation strategy considering our limited knowledge of TSD and the
effects of sex ratios on reproductive ecology in sea turtles. 40,41,104,105 Historically, sex ratio
manipulations began as an unintentional byproduct of conservation practices for protecting eggs. In some conservation programs, eggs were transferred to polystyrene boxes
and incubated in egg hatcheries to prevent predation and poaching, and to enhance
hatching success. 106 This practice can skew sex ratios, often by cooling the eggs and thus
increasing the production of males. 24,106 Some conservation programs use egg hatcheries
in which eggs are moved to protected locations and buried. This practice has the potential
of altering incubation temperatures. 107 As an example, the majority of Kemp’s ridley
eggs have been moved to egg hatcheries for several decades. 108,109 Evaluation of hatchling
sex ratios from those hatcheries in recent years has indicated a strong female bias in this
recovering species. 76 It is not clear whether this bias reflects the natural sex ratio that
would be produced if nests were left in situ, but the egg corrals most certainly do not
contain the diversity of incubation temperatures that are present on the natural nesting
beach. Regardless, it is clear that sex ratios can be manipulated, so the question is whether
sex ratios should be intentionally manipulated to enhance the recovery of a population.
On the surface it seems logical that strong male biases would not be advantageous
for the recovery of a population, and that the production of female biases could
enhance recovery by increasing egg production. 40 However, several factors should
be considered prior to such manipulations. First, it is not clear what proportion of
males is needed for successful fertilization of most or all females in a population. 41,
104 Even if a small minority of males could fertilize a large majority of females, the
artificial skewing of sex ratios could alter ecological factors such as intra- and
intersexual competition, sperm competition, and multiple paternity, which might
affect the reproductive ecology and evolution of a species. 104 Thus, intentionally
producing a female-biased sex ratio may have both advantages and disadvantages.
At the very least, nesting beach conservation programs should attempt to monitor
hatchling sex ratios, especially if nests are translocated to hatcheries or to safer locations
on the beach (e.g., above high tide line). If egg hatcheries are used, the resulting sex
ratio should be considered when choosing the location of the hatchery. 107 It may be useful
to have two hatcheries with different thermal environments that would allow the production of males or females, depending on the hatchery in which eggs are placed. 40,41 For
egg hatcheries, a decision must be made about a desired sex ratio. One option would be
to monitor incubation temperatures in natural nests on the nesting beach and attempt to
duplicate the natural sex ratio. If the natural sex ratio is not known or cannot be predicted,
an alternative is to choose a sex ratio based on its potential for enhancing the recovery
of the population (discussed above) or based on sex ratios from other populations. As
1123 book.book Page 122 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
variations, which suggest that multiyear data are critical to understanding sex ratio
dynamics of sea turtle populations. Multiyear studies of sex ratios from a nesting
beach should consistently address spatial and temporal diversity of nests during each
of the nesting seasons to make year-to-year comparisons meaningful.
4.3.8 MANIPULATION OF HATCHLING SEX RATIOS
Because sea turtles possess TSD, it is possible to artificially alter hatchling sex ratios.
However, there has been considerable debate as to whether sex ratio manipulation is an
appropriate conservation strategy considering our limited knowledge of TSD and the
effects of sex ratios on reproductive ecology in sea turtles. 40,41,104,105 Historically, sex ratio
manipulations began as an unintentional byproduct of conservation practices for protecting eggs. In some conservation programs, eggs were transferred to polystyrene boxes
and incubated in egg hatcheries to prevent predation and poaching, and to enhance
hatching success. 106 This practice can skew sex ratios, often by cooling the eggs and thus
increasing the production of males. 24,106 Some conservation programs use egg hatcheries
in which eggs are moved to protected locations and buried. This practice has the potential
of altering incubation temperatures. 107 As an example, the majority of Kemp’s ridley
eggs have been moved to egg hatcheries for several decades. 108,109 Evaluation of hatchling
sex ratios from those hatcheries in recent years has indicated a strong female bias in this
recovering species. 76 It is not clear whether this bias reflects the natural sex ratio that
would be produced if nests were left in situ, but the egg corrals most certainly do not
contain the diversity of incubation temperatures that are present on the natural nesting
beach. Regardless, it is clear that sex ratios can be manipulated, so the question is whether
sex ratios should be intentionally manipulated to enhance the recovery of a population.
On the surface it seems logical that strong male biases would not be advantageous
for the recovery of a population, and that the production of female biases could
enhance recovery by increasing egg production. 40 However, several factors should
be considered prior to such manipulations. First, it is not clear what proportion of
males is needed for successful fertilization of most or all females in a population. 41,
104 Even if a small minority of males could fertilize a large majority of females, the
artificial skewing of sex ratios could alter ecological factors such as intra- and
intersexual competition, sperm competition, and multiple paternity, which might
affect the reproductive ecology and evolution of a species. 104 Thus, intentionally
producing a female-biased sex ratio may have both advantages and disadvantages.
At the very least, nesting beach conservation programs should attempt to monitor
hatchling sex ratios, especially if nests are translocated to hatcheries or to safer locations
on the beach (e.g., above high tide line). If egg hatcheries are used, the resulting sex
ratio should be considered when choosing the location of the hatchery. 107 It may be useful
to have two hatcheries with different thermal environments that would allow the production of males or females, depending on the hatchery in which eggs are placed. 40,41 For
egg hatcheries, a decision must be made about a desired sex ratio. One option would be
to monitor incubation temperatures in natural nests on the nesting beach and attempt to
duplicate the natural sex ratio. If the natural sex ratio is not known or cannot be predicted,
an alternative is to choose a sex ratio based on its potential for enhancing the recovery
of the population (discussed above) or based on sex ratios from other populations. As
1123 book.book Page 122 Monday, November 11, 2002 11:11 AM