182
The Biology of Sea Turtles, Vol. II
hatchlings, indicating an increase in the anaerobic component (although VO 2 in both
conditions was higher than in resting animals). Similarly, Wyneken (1992) reported
that the cost of locomotion in leatherback hatchlings is as much as 20% lower during
frenzy swimming than in green and loggerhead hatchlings, with leatherbacks having
the slowest swimming speeds, stroke rates, and lowest metabolic rates. Because
leatherback turtles of less than 110 cm CCL are not found in waters above 34∞
latitude (26∞C) (Eckert, 2000), it has been suggested that leatherback hatchlings may
become active, distance swimmers early in development, allowing them to forage
in upwelling and convergence zones rather than being swept as passive feeders into
the ocean gyres. Thus, although the physical requirements of emergence, crawling,
and frenzy and postfrenzy swimming are common to all sea turtle species, the
physiological stresses that these activities place on hatchlings again vary with interspecific metabolic differences.
6.4 RESPONSES TO STRESS
Stress responses may be expressed at multiple levels, from the immediate effects of
acute stress on catecholamine levels to long-term effects such as immune suppression, changes in gene expression, and population effects, i.e., decreased reproductive
rates. Harmful effects from both anthropogenic and natural insults include compromised physiology, impaired immune function, and an increase in the incidence of
disease (Lutz, 1998). Immunosuppression is strongly correlated with GTFP in green
turtles in Florida (Cray et al., in press; Sposato et al., 2002) and Hawaii (Aguirre
et al., 1995), and it is likely that immunosuppressed turtles will suffer from other
disease or parasite stressors as well.
6.4.1 NEUROENDOCRINE RESPONSES (STRESS HORMONES)
Selye (1936) proposed that different stresses produced a similar set of responses,
which he called the general adaptation syndrome (GAS), i.e., alarm–resistance–exhaustion. In this widely adopted scheme, the primary response is at the
neuroendocrine level, involving the hypothalamus–pituitary–adrenocorticoid axis. It
is often identified as an increase in blood cortisol levels and has been taken as the
stress-defining response (Nelson and Demas, 1996). Stress-related changes in corticosteroids are well documented in both freshwater and sea turtles.
Capture stress produces changes in corticosterone levels, but there are seasonal
and size differences (Gregory et al., 1996; Gregory and Schmid, 2001). In examining
acute captivity stress responses, Gregory et al. (1996) found that smaller turtles had
higher levels of corticosterone in summer than did larger animals, whereas corticosterone levels were suppressed in both size classes in winter. It was suggested that
the lower responses exhibited by large turtles in summer were related to reproductive
condition, a finding supported by reduced adrenocortical function in heat-stressed
breeding green turtles and in arribada olive ridleys exposed to turning stress (Jessop
et al., 2000; Valverde et al., 1999). Similarly, male olive ridleys captured by hand
and held in crowded conditions exhibited significantly higher corticosterone levels
than females held under the same conditions (Schwantes, 1986). The stress of
1123 book.book Page 182 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
hatchlings, indicating an increase in the anaerobic component (although VO 2 in both
conditions was higher than in resting animals). Similarly, Wyneken (1992) reported
that the cost of locomotion in leatherback hatchlings is as much as 20% lower during
frenzy swimming than in green and loggerhead hatchlings, with leatherbacks having
the slowest swimming speeds, stroke rates, and lowest metabolic rates. Because
leatherback turtles of less than 110 cm CCL are not found in waters above 34∞
latitude (26∞C) (Eckert, 2000), it has been suggested that leatherback hatchlings may
become active, distance swimmers early in development, allowing them to forage
in upwelling and convergence zones rather than being swept as passive feeders into
the ocean gyres. Thus, although the physical requirements of emergence, crawling,
and frenzy and postfrenzy swimming are common to all sea turtle species, the
physiological stresses that these activities place on hatchlings again vary with interspecific metabolic differences.
6.4 RESPONSES TO STRESS
Stress responses may be expressed at multiple levels, from the immediate effects of
acute stress on catecholamine levels to long-term effects such as immune suppression, changes in gene expression, and population effects, i.e., decreased reproductive
rates. Harmful effects from both anthropogenic and natural insults include compromised physiology, impaired immune function, and an increase in the incidence of
disease (Lutz, 1998). Immunosuppression is strongly correlated with GTFP in green
turtles in Florida (Cray et al., in press; Sposato et al., 2002) and Hawaii (Aguirre
et al., 1995), and it is likely that immunosuppressed turtles will suffer from other
disease or parasite stressors as well.
6.4.1 NEUROENDOCRINE RESPONSES (STRESS HORMONES)
Selye (1936) proposed that different stresses produced a similar set of responses,
which he called the general adaptation syndrome (GAS), i.e., alarm–resistance–exhaustion. In this widely adopted scheme, the primary response is at the
neuroendocrine level, involving the hypothalamus–pituitary–adrenocorticoid axis. It
is often identified as an increase in blood cortisol levels and has been taken as the
stress-defining response (Nelson and Demas, 1996). Stress-related changes in corticosteroids are well documented in both freshwater and sea turtles.
Capture stress produces changes in corticosterone levels, but there are seasonal
and size differences (Gregory et al., 1996; Gregory and Schmid, 2001). In examining
acute captivity stress responses, Gregory et al. (1996) found that smaller turtles had
higher levels of corticosterone in summer than did larger animals, whereas corticosterone levels were suppressed in both size classes in winter. It was suggested that
the lower responses exhibited by large turtles in summer were related to reproductive
condition, a finding supported by reduced adrenocortical function in heat-stressed
breeding green turtles and in arribada olive ridleys exposed to turning stress (Jessop
et al., 2000; Valverde et al., 1999). Similarly, male olive ridleys captured by hand
and held in crowded conditions exhibited significantly higher corticosterone levels
than females held under the same conditions (Schwantes, 1986). The stress of
1123 book.book Page 182 Monday, November 11, 2002 11:11 AM