248
The Biology of Sea Turtles, Vol. II
in that oceanographic and meteorological factors (e.g., currents and winds) have the
greatest influence on the movements and distribution patterns of these turtles,
although the post-hatchlings may actively position themselves using magnetic orientation cues to maximize the likelihood of successful transport (Lohmann and
Lohmann, in press). After a developmental period in the oceanic zone lasting from
7 to 11.5 years, when the turtles reach a size of 46–64 cm curved carapace length
(Bjorndal et al., 2000a; Bjorndal et al., in review), juvenile loggerheads in the Atlantic leave the oceanic zone and complete their development in the neritic zone (Musick
and Limpus, 1997; Bjorndal et al., 2001; Bolten, in press).
Other Type 2 species recruit to neritic habitats at smaller sizes. Green turtles
and hawksbills appear in neritic foraging grounds at about 20–35 cm carapace length
(CL) and Kemp’s ridleys at 20–25 cm CL (Bjorndal, 1997; Musick and Limpus,
1997). On the basis of size at recruitment to neritic habitats, the durations of the
oceanic stages in these species may be shorter than that of Atlantic loggerheads.
Size at recruitment is apparently not a function of size at maturity. Adult size of
loggerheads falls between those of Kemp’s ridleys and green turtles (Miller, 1997).
Recruitment from the oceanic, where the turtles are primarily epipelagic, to the
neritic, where they are primarily benthic, may involve another transition period
before the juvenile turtles become fully neritic (Kamezaki and Matsui, 1997; Laurent
et al., 1998; Bolten, in press; Tiwari et al., in press). Adults of Type 2 species may
leave neritic habitats during their reproductive migrations, which may involve oceanic migration corridors between the adult foraging areas (neritic) and internesting
habitat (also neritic). Figure 9.2 presents the details of the loggerhead life history
from the North Atlantic.
9.3.3 T YPE 3: T HE O CEANIC D EVELOPMENTAL P ATTERN
The Type 3 life history pattern is characterized by both developmental and adult
stages occurring completely in the oceanic zone (Figure 9.1, bottom panel). Of
course, post-hatchlings, once they leave the nesting beach, must traverse the neritic
zone to reach the oceanic zone, and adults must return to the neritic zone for
reproduction. The leatherback ( Dermochelys coriacea ) and olive ridley (East Pacific
populations) are believed to exhibit this life history pattern. Very little is known
about the biology (e.g., oceanic distribution, diet, or growth rates) of early developmental stages for olive ridleys and leatherbacks, but it is assumed that the juvenile
stages occur in the oceanic zone.
Leatherbacks and olive ridleys are very different in many aspects, such as body
size, thermal regulation, and foraging behavior. The leatherback is the largest sea
turtle species, with a mean adult size of 149 cm CL, whereas the olive ridley is one
of the smallest species, with a mean adult CL of 66 cm (Van Buskirk and Crowder,
1994). Leatherbacks are able to maintain a body temperature 15 ∞ C above ambient
and forage in waters with temperatures as low as 0–15 ∞ C (Spotila et al., 1997). The
olive ridley maintains a body temperature at most a few degrees above ambient
(Spotila et al., 1997) and appears to be limited to warmer, tropical waters (Pitman,
1990; 1993; Polovina et al., in review). Leatherbacks are active predators, and may
not undergo a substantial diet shift as they grow because the ability to capture and
1123 book.book Page 248 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
in that oceanographic and meteorological factors (e.g., currents and winds) have the
greatest influence on the movements and distribution patterns of these turtles,
although the post-hatchlings may actively position themselves using magnetic orientation cues to maximize the likelihood of successful transport (Lohmann and
Lohmann, in press). After a developmental period in the oceanic zone lasting from
7 to 11.5 years, when the turtles reach a size of 46–64 cm curved carapace length
(Bjorndal et al., 2000a; Bjorndal et al., in review), juvenile loggerheads in the Atlantic leave the oceanic zone and complete their development in the neritic zone (Musick
and Limpus, 1997; Bjorndal et al., 2001; Bolten, in press).
Other Type 2 species recruit to neritic habitats at smaller sizes. Green turtles
and hawksbills appear in neritic foraging grounds at about 20–35 cm carapace length
(CL) and Kemp’s ridleys at 20–25 cm CL (Bjorndal, 1997; Musick and Limpus,
1997). On the basis of size at recruitment to neritic habitats, the durations of the
oceanic stages in these species may be shorter than that of Atlantic loggerheads.
Size at recruitment is apparently not a function of size at maturity. Adult size of
loggerheads falls between those of Kemp’s ridleys and green turtles (Miller, 1997).
Recruitment from the oceanic, where the turtles are primarily epipelagic, to the
neritic, where they are primarily benthic, may involve another transition period
before the juvenile turtles become fully neritic (Kamezaki and Matsui, 1997; Laurent
et al., 1998; Bolten, in press; Tiwari et al., in press). Adults of Type 2 species may
leave neritic habitats during their reproductive migrations, which may involve oceanic migration corridors between the adult foraging areas (neritic) and internesting
habitat (also neritic). Figure 9.2 presents the details of the loggerhead life history
from the North Atlantic.
9.3.3 T YPE 3: T HE O CEANIC D EVELOPMENTAL P ATTERN
The Type 3 life history pattern is characterized by both developmental and adult
stages occurring completely in the oceanic zone (Figure 9.1, bottom panel). Of
course, post-hatchlings, once they leave the nesting beach, must traverse the neritic
zone to reach the oceanic zone, and adults must return to the neritic zone for
reproduction. The leatherback ( Dermochelys coriacea ) and olive ridley (East Pacific
populations) are believed to exhibit this life history pattern. Very little is known
about the biology (e.g., oceanic distribution, diet, or growth rates) of early developmental stages for olive ridleys and leatherbacks, but it is assumed that the juvenile
stages occur in the oceanic zone.
Leatherbacks and olive ridleys are very different in many aspects, such as body
size, thermal regulation, and foraging behavior. The leatherback is the largest sea
turtle species, with a mean adult size of 149 cm CL, whereas the olive ridley is one
of the smallest species, with a mean adult CL of 66 cm (Van Buskirk and Crowder,
1994). Leatherbacks are able to maintain a body temperature 15 ∞ C above ambient
and forage in waters with temperatures as low as 0–15 ∞ C (Spotila et al., 1997). The
olive ridley maintains a body temperature at most a few degrees above ambient
(Spotila et al., 1997) and appears to be limited to warmer, tropical waters (Pitman,
1990; 1993; Polovina et al., in review). Leatherbacks are active predators, and may
not undergo a substantial diet shift as they grow because the ability to capture and
1123 book.book Page 248 Monday, November 11, 2002 11:11 AM