Adult Migrations and Habitat Use
227
undertake reproductive migration to nesting beaches every 2–3 years, where they
oviposit on average five to six clutches at 9-day intervals (Boulon et al., 1996;
Steyermark et al., 1996). Estimating fecundity for leatherbacks is challenging
because females do not display strong beach fidelity. Females may travel among
adjacent (Steyermark et al., 1996) or distant beaches (Keinath and Musick, 1993)
within a nesting season.
After the nesting season, females migrate long distances across deep oceanic
waters (Morreale et al., 1994; 1996; Eckert and Sarti, 1997; Eckert, 1998; Hughes
et al., 1998; Lutcavage et al., in press) and in some instances across ocean basins
(Eckert, 1998). In some regions, migratory corridors along deepwater bathymetric
contours have been described, with multiple postnesting females from the same beach
migrating through these areas in subsequent years (Morreale et al., 1994; 1996). However, in other regions no such corridors have been detected for postnesting female
cohorts (Eckert, 1998). Leatherbacks do not migrate to resident feeding grounds, as
has been well described for some species. Instead, leatherbacks appear to swim continuously (Eckert and Sarti, 1997; Eckert, 1998), possibly to areas of high food
concentration (Grant et al., 1996; Eckert and Sarti, 1997), where they appear to feed
on organisms associated with the deep scattering layer (Eckert et al., 1989).
Navigational cues used by leatherbacks during migration are not known, but
potentially important cues suggested thus far include ocean currents, ocean fronts,
bathymetric features, and magnetic cues (Morreale et al., 1994; 1996; Lutcavage,
1996).
8.3 OLIVE RIDLEY, LEPIDOCHELYS OLIVACEA
The olive ridley has a circumtropical distribution, occurring in the Atlantic, Pacific,
and Indian Oceans (Pritchard, 1969). Knowledge of olive ridley migrations is fragmentary throughout most of its range, with the exception of the eastern Pacific and
the northern Indian Ocean. The olive ridley is highly migratory and spends most of
its nonbreeding life cycle in the oceanic zone (Cornelius and Robinson, 1986;
Pitman, 1990; 1993; Arenas and Hall, 1992; Plotkin, 1994; Plotkin et al., 1994;
1995; Beavers, 1996; Beavers and Cassano, 1996).
Olive ridleys occupy the neritic zone during the breeding season. Reproductively
active males and females migrate toward the coast and aggregate at nearshore
breeding grounds located near beaches where mass nesting emergences (commonly
known as arribadas) also occur (Pritchard, 1969; Hughes and Richard, 1974; Cornelius, 1986; Dash and Kar, 1990; Plotkin et al., 1991; 1996; Kalb et al., 1995;
1997; Pandav et al., 2000). A significant proportion of the breeding also takes place
far from shore (Pitman, 1990; Kopitsky et al., 2000), and some males and females
may not migrate to nearshore breeding aggregations. Some males appear to remain
in oceanic waters, are nonaggregated, and mate opportunistically as they intercept
females en route to nearshore breeding grounds and nesting beaches (Plotkin, 1994;
Plotkin et al., 1994; 1996; Kopitsky et al., 2000).
After mating, females remain nearshore for several weeks to several months.
Solitary nesters emerge onto beaches to lay eggs individually throughout much of
the species’ range. Solitary nesters have weak site fidelity (Kalb, 1999), lay two
1123 book.book Page 227 Monday, November 11, 2002 11:11 AM
227
undertake reproductive migration to nesting beaches every 2–3 years, where they
oviposit on average five to six clutches at 9-day intervals (Boulon et al., 1996;
Steyermark et al., 1996). Estimating fecundity for leatherbacks is challenging
because females do not display strong beach fidelity. Females may travel among
adjacent (Steyermark et al., 1996) or distant beaches (Keinath and Musick, 1993)
within a nesting season.
After the nesting season, females migrate long distances across deep oceanic
waters (Morreale et al., 1994; 1996; Eckert and Sarti, 1997; Eckert, 1998; Hughes
et al., 1998; Lutcavage et al., in press) and in some instances across ocean basins
(Eckert, 1998). In some regions, migratory corridors along deepwater bathymetric
contours have been described, with multiple postnesting females from the same beach
migrating through these areas in subsequent years (Morreale et al., 1994; 1996). However, in other regions no such corridors have been detected for postnesting female
cohorts (Eckert, 1998). Leatherbacks do not migrate to resident feeding grounds, as
has been well described for some species. Instead, leatherbacks appear to swim continuously (Eckert and Sarti, 1997; Eckert, 1998), possibly to areas of high food
concentration (Grant et al., 1996; Eckert and Sarti, 1997), where they appear to feed
on organisms associated with the deep scattering layer (Eckert et al., 1989).
Navigational cues used by leatherbacks during migration are not known, but
potentially important cues suggested thus far include ocean currents, ocean fronts,
bathymetric features, and magnetic cues (Morreale et al., 1994; 1996; Lutcavage,
1996).
8.3 OLIVE RIDLEY, LEPIDOCHELYS OLIVACEA
The olive ridley has a circumtropical distribution, occurring in the Atlantic, Pacific,
and Indian Oceans (Pritchard, 1969). Knowledge of olive ridley migrations is fragmentary throughout most of its range, with the exception of the eastern Pacific and
the northern Indian Ocean. The olive ridley is highly migratory and spends most of
its nonbreeding life cycle in the oceanic zone (Cornelius and Robinson, 1986;
Pitman, 1990; 1993; Arenas and Hall, 1992; Plotkin, 1994; Plotkin et al., 1994;
1995; Beavers, 1996; Beavers and Cassano, 1996).
Olive ridleys occupy the neritic zone during the breeding season. Reproductively
active males and females migrate toward the coast and aggregate at nearshore
breeding grounds located near beaches where mass nesting emergences (commonly
known as arribadas) also occur (Pritchard, 1969; Hughes and Richard, 1974; Cornelius, 1986; Dash and Kar, 1990; Plotkin et al., 1991; 1996; Kalb et al., 1995;
1997; Pandav et al., 2000). A significant proportion of the breeding also takes place
far from shore (Pitman, 1990; Kopitsky et al., 2000), and some males and females
may not migrate to nearshore breeding aggregations. Some males appear to remain
in oceanic waters, are nonaggregated, and mate opportunistically as they intercept
females en route to nearshore breeding grounds and nesting beaches (Plotkin, 1994;
Plotkin et al., 1994; 1996; Kopitsky et al., 2000).
After mating, females remain nearshore for several weeks to several months.
Solitary nesters emerge onto beaches to lay eggs individually throughout much of
the species’ range. Solitary nesters have weak site fidelity (Kalb, 1999), lay two
1123 book.book Page 227 Monday, November 11, 2002 11:11 AM