230
The Biology of Sea Turtles, Vol. II
Very little is known about hawksbill reproductive migrations from foraging areas
to breeding grounds. Females migrate to nest at their natal beaches (Bass, 1999) every
2–3 years (Witzell, 1983). Females inhabiting the same foraging area do not all migrate
to the same nesting beach (Miller et al., 1998). Mating is not well documented for this
species, but it has been observed in the shallow waters adjacent to nesting beaches
(Witzell, 1983) and probably occurs approximately 30 days prior to first nesting
(Owens, 1980b). Hawksbills are solitary nesters that lay four to seven clutches every
14–16 days (Witzell, 1983). Females remain nearshore the nesting beach during the
internesting period (Starbird, 1993; Starbird et al., 1999). As soon as the last nest is
oviposited, females begin postnesting migrations back to foraging areas (Starbird,
1993; Starbird et al., 1999; Mortimer and Balazs, 2000; Horrocks et al., 2001).
Postnesting hawksbills migrate to specific foraging areas within short range
(25–200 km) (Ellis et al., 2000; Hillis-Starr et al., 2000; Mortimer and Balazs, 2000;
Horrocks et al., 2001; Lageux et al., in press) and long range (200 km or more)
(Byles and Swimmer, 1994; Miller et al., 1998; Horrocks et al., 2001; Prieto et al.,
2001; Lageux et al., in press) of their nesting beaches. Such variation in migratory
behavior is found among females nesting at the same beaches (Miller et al., 1998;
Horrocks et al., 2001; Prieto et al., 2001). No apparent patterns have emerged to
explain why some females migrate short distances while others bypass reefs close
to their nesting beaches and migrate greater distances.
Both short-distance and long-distance migrations appear to be relatively quick,
directed movements that may occur across deep oceanic waters or channels (Ellis
et al., 2000; Horrocks et al., 2001) or shallow coastal waters (Ellis et al., 2000).
Once a female reaches her foraging ground, she remains resident there (Ellis et al.,
2000; Mortimer and Balazs, 2000), presumably until her next reproductive migration.
8.6 FLATBACK, NATATOR DEPRESSUS
The flatback has the most restricted migratory range of all sea turtles. It is endemic
to the tropical waters of the Australian continental shelf (Limpus et al., 1981),
occurring in shallow, turbid waters and bays (Limpus et al., 1983; 1989). Flatbacks
were once characterized as nonmigratory (Hendrickson, 1980), but tagging studies
have confirmed that they do undertake long-distance migrations between foraging
and breeding areas (Limpus et al., 1981; 1983). Flatbacks nest on mainland beaches,
continental island beaches, and sand cays within Australian territorial waters on the
northeast coast (Limpus, 1971; Limpus et al., 1981; 1989), north coast (Limpus
et al., 1983; Guinea et al., 1991; Guinea, 1994), and west coast (Prince, 1994).
Foraging areas extend just beyond the Australian territorial waters into adjacent
waters of the Indonesian archipelago and Papuan coast (Parmenter, 1994).
Females migrate from foraging areas to nesting beaches on average every 1–3
years (Limpus et al., 1984; Parmenter, 1994). Females show strong site fidelity to
their nesting beaches (Limpus et al., 1984; Parmenter, 1994). Mating occurs in the
vicinity of the nesting beach approximately 1 month prior to the start of the nesting
season (Limpus et al., 1989; 1993). Nesting occurs year-round at some beaches
(Limpus et al., 1983; 1989) and seasonally at others (Limpus, 1971; Limpus et al.,
1123 book.book Page 230 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
Very little is known about hawksbill reproductive migrations from foraging areas
to breeding grounds. Females migrate to nest at their natal beaches (Bass, 1999) every
2–3 years (Witzell, 1983). Females inhabiting the same foraging area do not all migrate
to the same nesting beach (Miller et al., 1998). Mating is not well documented for this
species, but it has been observed in the shallow waters adjacent to nesting beaches
(Witzell, 1983) and probably occurs approximately 30 days prior to first nesting
(Owens, 1980b). Hawksbills are solitary nesters that lay four to seven clutches every
14–16 days (Witzell, 1983). Females remain nearshore the nesting beach during the
internesting period (Starbird, 1993; Starbird et al., 1999). As soon as the last nest is
oviposited, females begin postnesting migrations back to foraging areas (Starbird,
1993; Starbird et al., 1999; Mortimer and Balazs, 2000; Horrocks et al., 2001).
Postnesting hawksbills migrate to specific foraging areas within short range
(25–200 km) (Ellis et al., 2000; Hillis-Starr et al., 2000; Mortimer and Balazs, 2000;
Horrocks et al., 2001; Lageux et al., in press) and long range (200 km or more)
(Byles and Swimmer, 1994; Miller et al., 1998; Horrocks et al., 2001; Prieto et al.,
2001; Lageux et al., in press) of their nesting beaches. Such variation in migratory
behavior is found among females nesting at the same beaches (Miller et al., 1998;
Horrocks et al., 2001; Prieto et al., 2001). No apparent patterns have emerged to
explain why some females migrate short distances while others bypass reefs close
to their nesting beaches and migrate greater distances.
Both short-distance and long-distance migrations appear to be relatively quick,
directed movements that may occur across deep oceanic waters or channels (Ellis
et al., 2000; Horrocks et al., 2001) or shallow coastal waters (Ellis et al., 2000).
Once a female reaches her foraging ground, she remains resident there (Ellis et al.,
2000; Mortimer and Balazs, 2000), presumably until her next reproductive migration.
8.6 FLATBACK, NATATOR DEPRESSUS
The flatback has the most restricted migratory range of all sea turtles. It is endemic
to the tropical waters of the Australian continental shelf (Limpus et al., 1981),
occurring in shallow, turbid waters and bays (Limpus et al., 1983; 1989). Flatbacks
were once characterized as nonmigratory (Hendrickson, 1980), but tagging studies
have confirmed that they do undertake long-distance migrations between foraging
and breeding areas (Limpus et al., 1981; 1983). Flatbacks nest on mainland beaches,
continental island beaches, and sand cays within Australian territorial waters on the
northeast coast (Limpus, 1971; Limpus et al., 1981; 1989), north coast (Limpus
et al., 1983; Guinea et al., 1991; Guinea, 1994), and west coast (Prince, 1994).
Foraging areas extend just beyond the Australian territorial waters into adjacent
waters of the Indonesian archipelago and Papuan coast (Parmenter, 1994).
Females migrate from foraging areas to nesting beaches on average every 1–3
years (Limpus et al., 1984; Parmenter, 1994). Females show strong site fidelity to
their nesting beaches (Limpus et al., 1984; Parmenter, 1994). Mating occurs in the
vicinity of the nesting beach approximately 1 month prior to the start of the nesting
season (Limpus et al., 1989; 1993). Nesting occurs year-round at some beaches
(Limpus et al., 1983; 1989) and seasonally at others (Limpus, 1971; Limpus et al.,
1123 book.book Page 230 Monday, November 11, 2002 11:11 AM