150
The Biology of Sea Turtles, Vol. II
Although limited foraging has been recorded in gravid C. mydas females at
Raine Island (Queensland, Australia) (Tucker and Read, 2001), diet studies, visual
examination of GI tracts during laparoscopic examinations of gonads, and satellite
telemetry studies generally indicate that C. mydas is primarily aphagic during the
nesting season (Bjorndal, 1982; 1985; Balazs et al., 2000; Limpus, unpublished
data). Thus, before they depart their foraging habitat on a breeding migration,
females must allocate sufficient lipid reserves to allow for the entire season’s reproductive output and the return migration, ideally without compromising metabolic
processes. Nesting success (percent of nesting attempts that result in successful
oviposition) varies among species and populations, and is often lower than 100%
(Miller, 1997; Loop et al., 1995; Godley et al., 2001; Hamann, 2002). Correlative
evidence suggests that C. mydas females nesting in a year characterized by high
rates of unsuccessful nesting have higher rates of follicular atresia (Limpus et al.,
1991; 1993). Plasma triglyceride levels are significantly lower in female C. mydas
after prolonged periods (>3 days) of unsuccessful nesting (Hamann et al., 2002b).
Moreover, total lipid values in adipose tissue in gravid C. mydas with atretic ovaries
(Hamann et al., 2002b) are reduced and similar to levels in females after completion
of a nesting season (Kwan, 1994). An interesting question thus arises: How many
unsuccessful nesting attempts can an individual female sustain without its reducing
her potential reproductive output (through depleting energy stores)?
The end of the nesting season could be triggered by insufficient mature ovarian
follicles to produce another clutch. Alternatively, specific factors that signal the end
of the nesting season may well be related to body condition or environmental
conditions. In birds that undertake lengthy breeding seasons, or periods of aphagia,
their behavior appears to be tightly regulated by a genetically determined energy
threshold. Once body condition declines below this threshold and protein stores are
put at risk, refeeding is initiated (Cherel et al., 1988; Gauthier-Clerc et al., 2001).
From a physiological standpoint, several changes occur in sea turtles at the end of
the nesting season: plasma hormone (testosterone, estrogen, and corticosterone) and
plasma triglyceride levels typically decline to near basal levels, and total plasma
protein levels have been observed to increase (Licht et al., 1979; 1980; Wibbels
et al., 1990; Rostal et al., 1997; 1998; 2001; Whittier et al., 1997; Hamann et al.,
2002b). There are few data available examining seasonal changes in body condition
in sea turtles, and data from Limpus et al. (2001a) indicate that females nesting at
Bramble Cay lost an average of 0.9 kg following each clutch. Moreover, the lack
of a sharp increase in corticosterone at the end of the nesting season in female sea
turtles suggests that body condition probably does not decline to critical levels as it
does in birds (Whittier et al., 1997, Rostal et al., 2001; Hamann et al., 2002a).
Therefore, despite slight evidence for a shift toward protein catabolism in C. mydas
(Hamann et al., 2002b), potential metabolic signals in sea turtles are less clear.
5.5.9 ARRIBADAS AND YEAR-ROUND NESTING
Two important variations of the typical seasonal nesting pattern of sea turtles are
the mass nesting behavior observed in some populations of the genus Lepidochelys
and year round nesting seen in some populations of other species.
1123 book.book Page 150 Thursday, November 14, 2002 11:50 AM
The Biology of Sea Turtles, Vol. II
Although limited foraging has been recorded in gravid C. mydas females at
Raine Island (Queensland, Australia) (Tucker and Read, 2001), diet studies, visual
examination of GI tracts during laparoscopic examinations of gonads, and satellite
telemetry studies generally indicate that C. mydas is primarily aphagic during the
nesting season (Bjorndal, 1982; 1985; Balazs et al., 2000; Limpus, unpublished
data). Thus, before they depart their foraging habitat on a breeding migration,
females must allocate sufficient lipid reserves to allow for the entire season’s reproductive output and the return migration, ideally without compromising metabolic
processes. Nesting success (percent of nesting attempts that result in successful
oviposition) varies among species and populations, and is often lower than 100%
(Miller, 1997; Loop et al., 1995; Godley et al., 2001; Hamann, 2002). Correlative
evidence suggests that C. mydas females nesting in a year characterized by high
rates of unsuccessful nesting have higher rates of follicular atresia (Limpus et al.,
1991; 1993). Plasma triglyceride levels are significantly lower in female C. mydas
after prolonged periods (>3 days) of unsuccessful nesting (Hamann et al., 2002b).
Moreover, total lipid values in adipose tissue in gravid C. mydas with atretic ovaries
(Hamann et al., 2002b) are reduced and similar to levels in females after completion
of a nesting season (Kwan, 1994). An interesting question thus arises: How many
unsuccessful nesting attempts can an individual female sustain without its reducing
her potential reproductive output (through depleting energy stores)?
The end of the nesting season could be triggered by insufficient mature ovarian
follicles to produce another clutch. Alternatively, specific factors that signal the end
of the nesting season may well be related to body condition or environmental
conditions. In birds that undertake lengthy breeding seasons, or periods of aphagia,
their behavior appears to be tightly regulated by a genetically determined energy
threshold. Once body condition declines below this threshold and protein stores are
put at risk, refeeding is initiated (Cherel et al., 1988; Gauthier-Clerc et al., 2001).
From a physiological standpoint, several changes occur in sea turtles at the end of
the nesting season: plasma hormone (testosterone, estrogen, and corticosterone) and
plasma triglyceride levels typically decline to near basal levels, and total plasma
protein levels have been observed to increase (Licht et al., 1979; 1980; Wibbels
et al., 1990; Rostal et al., 1997; 1998; 2001; Whittier et al., 1997; Hamann et al.,
2002b). There are few data available examining seasonal changes in body condition
in sea turtles, and data from Limpus et al. (2001a) indicate that females nesting at
Bramble Cay lost an average of 0.9 kg following each clutch. Moreover, the lack
of a sharp increase in corticosterone at the end of the nesting season in female sea
turtles suggests that body condition probably does not decline to critical levels as it
does in birds (Whittier et al., 1997, Rostal et al., 2001; Hamann et al., 2002a).
Therefore, despite slight evidence for a shift toward protein catabolism in C. mydas
(Hamann et al., 2002b), potential metabolic signals in sea turtles are less clear.
5.5.9 ARRIBADAS AND YEAR-ROUND NESTING
Two important variations of the typical seasonal nesting pattern of sea turtles are
the mass nesting behavior observed in some populations of the genus Lepidochelys
and year round nesting seen in some populations of other species.
1123 book.book Page 150 Thursday, November 14, 2002 11:50 AM