226
The Biology of Sea Turtles, Vol. II
during migration. Hatchlings can perceive and respond to several environmental
cues, including magnetic field intensity (Lohmann and Lohmann, 1996), magnetic
inclination angle (Lohmann and Lohmann, 1994), visual cues (Mrosovsky and
Shettleworth, 1968), water temperature gradients (Owens, 1980a), wave direction
(Lohmann et al., 1990; Wyneken et al., 1990), and chemicals in the water (Grassman et al., 1984). Despite this wealth of information, it is quite tenable that
hatchlings rely on different cues than do adult turtles.
In the last decade, we have gained a much better understanding of the navigational abilities of adult sea turtles, but the mechanisms used to guide them during
migration remain speculative (Papi and Luschi, 1996; Papi et al., 2000). Movements
of sea turtles to specific sites (Papi et al., 1995; 1997) and their return to these areas
even after displacement (Luschi et al., 1996; Papi et al., 1997) confirm that sea turtles
do indeed navigate. Recent studies have suggested or demonstrated that these navigational feats may be guided by biological compasses (Papi and Luschi, 1996;
Luschi et al., 1998), currents (Morreale et al., 1996; Papi et al., 2000), waterborne
chemicals (Luschi et al., 1998; Papi et al., 2000), windborne information (Luschi
et al., 2001), bathymetric features (Morreale et al., 1994), and water temperature
(Plotkin, 1994).
Sea turtles evolved distinct migratory strategies during their evolutionary history
as they adapted to different ocean habitats (Hendrickson, 1980). These adaptations
are illustrated by the migratory and habitat use patterns that are beginning to emerge
following several decades of research. Interspecific and intraspecific variation in
migratory behavior exists among contemporary sea turtles, and it is probable that
considerable variation exists in navigational mechanisms used among and within
species as well.
The remainder of this chapter provides a summary of the current state of knowledge of adult sea turtle migration patterns and habitat use by each species and, where
available, the potential navigational mechanisms employed. Most of our knowledge
comes from studies conducted on postnesting females because these turtles are easy
to capture, mark, and tag. Overall, very little is known about adult male sea turtles.
8.2 LEATHERBACK, DERMOCHELYS CORIACEA
The leatherback is widely distributed throughout the world’s oceans from boreal to
tropical waters. Leatherbacks inhabit the oceanic zone, are highly migratory (Pritchard, 1973; 1976; Morreale et al., 1996; Hughes et al., 1998), and are capable of
transoceanic migrations (Eckert, 1998) and diving to great depths (Eckert et al.,
1989). Much of the details of leatherback migrations remain elusive, in part because
the turtles occur far from land and travel such great distances; however, recent and
ongoing studies will soon provide more specific information regarding the migratory
behavior of this ocean traveler (Eckert and Sarti, 1997; Eckert, 1998; Lutcavage
et al., in press).
Little is known of the prereproductive migrations of leatherbacks and the location
of breeding grounds; it is believed that they conform to the generalized model for
sea turtle reproduction (Owens, 1980b). Females migrate to nearshore waters of
tropical beaches several weeks prior to the nesting season. Most female leatherbacks
1123 book.book Page 226 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
during migration. Hatchlings can perceive and respond to several environmental
cues, including magnetic field intensity (Lohmann and Lohmann, 1996), magnetic
inclination angle (Lohmann and Lohmann, 1994), visual cues (Mrosovsky and
Shettleworth, 1968), water temperature gradients (Owens, 1980a), wave direction
(Lohmann et al., 1990; Wyneken et al., 1990), and chemicals in the water (Grassman et al., 1984). Despite this wealth of information, it is quite tenable that
hatchlings rely on different cues than do adult turtles.
In the last decade, we have gained a much better understanding of the navigational abilities of adult sea turtles, but the mechanisms used to guide them during
migration remain speculative (Papi and Luschi, 1996; Papi et al., 2000). Movements
of sea turtles to specific sites (Papi et al., 1995; 1997) and their return to these areas
even after displacement (Luschi et al., 1996; Papi et al., 1997) confirm that sea turtles
do indeed navigate. Recent studies have suggested or demonstrated that these navigational feats may be guided by biological compasses (Papi and Luschi, 1996;
Luschi et al., 1998), currents (Morreale et al., 1996; Papi et al., 2000), waterborne
chemicals (Luschi et al., 1998; Papi et al., 2000), windborne information (Luschi
et al., 2001), bathymetric features (Morreale et al., 1994), and water temperature
(Plotkin, 1994).
Sea turtles evolved distinct migratory strategies during their evolutionary history
as they adapted to different ocean habitats (Hendrickson, 1980). These adaptations
are illustrated by the migratory and habitat use patterns that are beginning to emerge
following several decades of research. Interspecific and intraspecific variation in
migratory behavior exists among contemporary sea turtles, and it is probable that
considerable variation exists in navigational mechanisms used among and within
species as well.
The remainder of this chapter provides a summary of the current state of knowledge of adult sea turtle migration patterns and habitat use by each species and, where
available, the potential navigational mechanisms employed. Most of our knowledge
comes from studies conducted on postnesting females because these turtles are easy
to capture, mark, and tag. Overall, very little is known about adult male sea turtles.
8.2 LEATHERBACK, DERMOCHELYS CORIACEA
The leatherback is widely distributed throughout the world’s oceans from boreal to
tropical waters. Leatherbacks inhabit the oceanic zone, are highly migratory (Pritchard, 1973; 1976; Morreale et al., 1996; Hughes et al., 1998), and are capable of
transoceanic migrations (Eckert, 1998) and diving to great depths (Eckert et al.,
1989). Much of the details of leatherback migrations remain elusive, in part because
the turtles occur far from land and travel such great distances; however, recent and
ongoing studies will soon provide more specific information regarding the migratory
behavior of this ocean traveler (Eckert and Sarti, 1997; Eckert, 1998; Lutcavage
et al., in press).
Little is known of the prereproductive migrations of leatherbacks and the location
of breeding grounds; it is believed that they conform to the generalized model for
sea turtle reproduction (Owens, 1980b). Females migrate to nearshore waters of
tropical beaches several weeks prior to the nesting season. Most female leatherbacks
1123 book.book Page 226 Monday, November 11, 2002 11:11 AM