Physiological and Genetic Responses to Environmental Stress
169
in temperatures ranging from 0 to 15°C (Goff and Lien, 1988). Frair et al. (1972)
reported a body temperature of 25.5°C for a leatherback held in 7.5°C water, which
makes the idea of a cold-stunned adult leatherback unlikely!
In addition to migrating toward warmer waters at the onset of the cold season,
larger turtles may physiologically avoid cold stunning by entering a hibernation-like
state. There is evidence that both green ( Chelonia agassizi ) and loggerhead turtles
bury themselves in bottom sediments for extended periods of time during winter
(Felger et al., 1976; Carr et al., 1980–81).
The recommended treatment for cold stunning is fairly straightforward: hold the
animals in warm water until their core temperature recovers (George, 1997). The
success rate is high — of the turtles treated at the New England Aquarium during
the 1999–2000 cold-stunning season, survival ranged from 66% ( C. mydas ) to 100%
( Caretta caretta ) (Still et al., in press). Holding the victims in fresh or brackish water
until salt gland function recovers has also been recommended (George, 1997).
6.3.1.2 Hyperthermia
Excessive heat exposure is also a stress to poikilotherms, though for sea turtles
hyperthermia would be a rare phenomenon when they are in the ocean. However,
increased water temperatures may indirectly increase stress on sea turtles, in that
increased surface temperatures increase the growth rates of both pathogens and toxic
phytoplankton.
High temperatures can, however, be experienced while they are on land, basking
or nesting.
In turtles basking at French Frigate Shoals (HI) carapace temperatures as high
as 42.8°C have been recorded (Whittow and Balazs, 1982). Behavioral adaptations
are used to moderate the ambient heat load. Surface temperatures can be reduced
as much as 10°C by flipping sand onto flippers and the carapace, and basking turtles
appear to choose cooler beaches (Whittow and Balazs, 1982).
Heat stress can be fatal for nesting females. Environmental temperatures above
40°C can result in stress for green sea turtles (see Spotila et al., 1997), whereas
excessive heat exposure routinely results in a high mortality (tens of turtles per day)
of postnesting females at the Raine Island (Australia) green turtle rookery (Jessop
et al., 2000). In the Raine Island study, an increase in body temperature of females
stranded on the beach from 28.2 to 40.7 ∞ C over 6 h resulted in a 16-fold mean
increase in plasma corticosterone (a hormonal marker of stress), to levels comparable
to those seen in animals subjected to 8 hr capture stress (Jessop et al., 2000). In the
soft-shelled turtle, Lissemys punctata punctata , increases in adrenomedullary function were detected as temperatures increased from 30 to 35 and 38°C, resulting in
increased levels of circulating epinephrine, norepinephrine, and glucose (Ray and
Maiti, 2001).
6.3.2 C HEMICAL P OLLUTANTS
Age, gender, and diet are all important factors in the potential for animals to be
affected by or bioaccumulate persistent pollutants, as is the identity and effects of
1123 book.book Page 169 Monday, November 11, 2002 11:11 AM
169
in temperatures ranging from 0 to 15°C (Goff and Lien, 1988). Frair et al. (1972)
reported a body temperature of 25.5°C for a leatherback held in 7.5°C water, which
makes the idea of a cold-stunned adult leatherback unlikely!
In addition to migrating toward warmer waters at the onset of the cold season,
larger turtles may physiologically avoid cold stunning by entering a hibernation-like
state. There is evidence that both green ( Chelonia agassizi ) and loggerhead turtles
bury themselves in bottom sediments for extended periods of time during winter
(Felger et al., 1976; Carr et al., 1980–81).
The recommended treatment for cold stunning is fairly straightforward: hold the
animals in warm water until their core temperature recovers (George, 1997). The
success rate is high — of the turtles treated at the New England Aquarium during
the 1999–2000 cold-stunning season, survival ranged from 66% ( C. mydas ) to 100%
( Caretta caretta ) (Still et al., in press). Holding the victims in fresh or brackish water
until salt gland function recovers has also been recommended (George, 1997).
6.3.1.2 Hyperthermia
Excessive heat exposure is also a stress to poikilotherms, though for sea turtles
hyperthermia would be a rare phenomenon when they are in the ocean. However,
increased water temperatures may indirectly increase stress on sea turtles, in that
increased surface temperatures increase the growth rates of both pathogens and toxic
phytoplankton.
High temperatures can, however, be experienced while they are on land, basking
or nesting.
In turtles basking at French Frigate Shoals (HI) carapace temperatures as high
as 42.8°C have been recorded (Whittow and Balazs, 1982). Behavioral adaptations
are used to moderate the ambient heat load. Surface temperatures can be reduced
as much as 10°C by flipping sand onto flippers and the carapace, and basking turtles
appear to choose cooler beaches (Whittow and Balazs, 1982).
Heat stress can be fatal for nesting females. Environmental temperatures above
40°C can result in stress for green sea turtles (see Spotila et al., 1997), whereas
excessive heat exposure routinely results in a high mortality (tens of turtles per day)
of postnesting females at the Raine Island (Australia) green turtle rookery (Jessop
et al., 2000). In the Raine Island study, an increase in body temperature of females
stranded on the beach from 28.2 to 40.7 ∞ C over 6 h resulted in a 16-fold mean
increase in plasma corticosterone (a hormonal marker of stress), to levels comparable
to those seen in animals subjected to 8 hr capture stress (Jessop et al., 2000). In the
soft-shelled turtle, Lissemys punctata punctata , increases in adrenomedullary function were detected as temperatures increased from 30 to 35 and 38°C, resulting in
increased levels of circulating epinephrine, norepinephrine, and glucose (Ray and
Maiti, 2001).
6.3.2 C HEMICAL P OLLUTANTS
Age, gender, and diet are all important factors in the potential for animals to be
affected by or bioaccumulate persistent pollutants, as is the identity and effects of
1123 book.book Page 169 Monday, November 11, 2002 11:11 AM