Critical Approaches to Sex Determination in Sea Turtles
115
beach. Beach nourishment projects have the potential of changing the thermal characteristics of the beach and thus incubation temperatures. 42 Furthermore, housing
developments on nesting beaches have the potential of limiting the nesting area (and
thus the range of thermal environments) and also shading nests. 42,61
4.3.5 SEX RATIOS IN IMMATURE AND ADULT PORTIONS OF A
POPULATION
Sex ratios in other size classes in sea turtle populations (e.g., immature and adult)
are also of interest. These groups represent a condensation of many years of hatchling
sex ratios, although it must be kept in mind that these sex ratios could also reflect
potential sex-specific mortality during development or as adults. For example, energy
expenditures associated with egg production and nesting, together with movements
onto nesting beaches, could increase the mortality of adult females relative to males.
It is also plausible that sex-specific hatchling and post-hatchling mortality could
occur because of seasonal variation in hatchling sex ratios. For example, hatchlings
produced early in the nesting season might be predominantly one sex and may
experience different food availability and predation from hatchlings produced later
in the nesting season (which could be predominantly the other sex). Knowledge of
sex ratios in the various size–age classes within a population is necessary to begin
understanding the potential dynamics of sex ratios within a population. Ultimately,
such knowledge would provide insight on the long-term effects of sex ratios on the
reproductive ecology of a population.
Our knowledge of adult sex ratios in sea turtle populations is limited because
of a number of factors. First, it is logistically difficult to sample adult sea turtles in
the ocean. Another problem relates to sex-specific migration patterns of adult males
vs. females. For example, Henwood 75 found an approximate 1:1 sex ratio of adult
loggerheads captured in waters near Cape Canaveral, FL; however, he recorded
seasonal differences in the abundance of adult males vs. adult females. A study of
green turtles of the southern Great Barrier Reef reported a 1:1 adult sex ratio, but
suggested that the ratio may have been due to sex-biased migratory patterns in which
adult males stayed closer to the breeding grounds (and sampling areas) than did the
adult females. 62,63
Human impacts may also affect adult sex ratios. In a study of adult green turtles
in Oman, Ross 68 reported an overall sex ratio that was not significantly different
from 1:1, but found an excess of females or males in several locations. In the case
of excess of males, it was noted that fishermen in that area preferentially hunted for
females. 68 Several studies have reported female-biased sex ratios of green turtles
based on commercial catches, 64–67 but there is the potential of sampling bias because
of fishing practices. 68A Thus, a number of potential problems can affect the results
of adult sex ratio studies. Accurate evaluation of adult sex ratios requires knowledge
of migratory behavior (e.g., timing and specific migratory routes) as well as other
factors that might impact the sex ratio of turtles captured in a particular sampling
location. Regardless of the associated difficulties, studies of adult sex ratios are
necessary to fully understand the potential variation and dynamics of sex ratios
within a sea turtle population.
1123 book.book Page 115 Monday, November 11, 2002 11:11 AM
115
beach. Beach nourishment projects have the potential of changing the thermal characteristics of the beach and thus incubation temperatures. 42 Furthermore, housing
developments on nesting beaches have the potential of limiting the nesting area (and
thus the range of thermal environments) and also shading nests. 42,61
4.3.5 SEX RATIOS IN IMMATURE AND ADULT PORTIONS OF A
POPULATION
Sex ratios in other size classes in sea turtle populations (e.g., immature and adult)
are also of interest. These groups represent a condensation of many years of hatchling
sex ratios, although it must be kept in mind that these sex ratios could also reflect
potential sex-specific mortality during development or as adults. For example, energy
expenditures associated with egg production and nesting, together with movements
onto nesting beaches, could increase the mortality of adult females relative to males.
It is also plausible that sex-specific hatchling and post-hatchling mortality could
occur because of seasonal variation in hatchling sex ratios. For example, hatchlings
produced early in the nesting season might be predominantly one sex and may
experience different food availability and predation from hatchlings produced later
in the nesting season (which could be predominantly the other sex). Knowledge of
sex ratios in the various size–age classes within a population is necessary to begin
understanding the potential dynamics of sex ratios within a population. Ultimately,
such knowledge would provide insight on the long-term effects of sex ratios on the
reproductive ecology of a population.
Our knowledge of adult sex ratios in sea turtle populations is limited because
of a number of factors. First, it is logistically difficult to sample adult sea turtles in
the ocean. Another problem relates to sex-specific migration patterns of adult males
vs. females. For example, Henwood 75 found an approximate 1:1 sex ratio of adult
loggerheads captured in waters near Cape Canaveral, FL; however, he recorded
seasonal differences in the abundance of adult males vs. adult females. A study of
green turtles of the southern Great Barrier Reef reported a 1:1 adult sex ratio, but
suggested that the ratio may have been due to sex-biased migratory patterns in which
adult males stayed closer to the breeding grounds (and sampling areas) than did the
adult females. 62,63
Human impacts may also affect adult sex ratios. In a study of adult green turtles
in Oman, Ross 68 reported an overall sex ratio that was not significantly different
from 1:1, but found an excess of females or males in several locations. In the case
of excess of males, it was noted that fishermen in that area preferentially hunted for
females. 68 Several studies have reported female-biased sex ratios of green turtles
based on commercial catches, 64–67 but there is the potential of sampling bias because
of fishing practices. 68A Thus, a number of potential problems can affect the results
of adult sex ratio studies. Accurate evaluation of adult sex ratios requires knowledge
of migratory behavior (e.g., timing and specific migratory routes) as well as other
factors that might impact the sex ratio of turtles captured in a particular sampling
location. Regardless of the associated difficulties, studies of adult sex ratios are
necessary to fully understand the potential variation and dynamics of sex ratios
within a sea turtle population.
1123 book.book Page 115 Monday, November 11, 2002 11:11 AM