Variation in Sea Turtle Life History Patterns
247
Walker, 1994; Musick and Limpus, 1997). However, the size difference between
flatback turtles and those species exhibiting Type 2 or 3 patterns does not seem to
be great enough to make a significant difference with respect to marine predators.
The larger hatchling size of the flatback may be a response to terrestrial predators
and the need to survive the predator gauntlet from the nest to the water. The larger
size of flatback hatchlings allows them to escape some bird and crab predators on
Australian beaches that prey upon the green turtle ( C. mydas ) and loggerhead
hatchlings (Limpus, 1971). The fact that other sea turtle species have not also
responded to terrestrial predators by increasing hatchling body size suggests that
the selective pressures leading to the increased size of flatback hatchlings are not
fully understood. Knowledge of the selective advantages of large hatchling size may
be critical for understanding the success of the Type 1 life history pattern.
The early juvenile stage of Type 1 species (including post-hatchlings) probably
feeds on the surface and within the water column, and may later develop a benthic
feeding strategy once the turtle has gained buoyancy control and can dive to the
sea floor. In the shallow waters that Type 1 species inhabit, their foraging behavior
may be a mix of pelagic and benthic feeding throughout life. Support for this
mixed foraging strategy is seen in the diet of both small and large flatback turtles
(Limpus et al., 1988; Zangerl et al., 1988). However, the number of samples that
has been evaluated is too small to be conclusive; more studies on the diet of
flatbacks are needed.
9.3.2 T YPE 2: T HE O CEANIC –N ERITIC D EVELOPMENTAL P ATTERN
The Type 2 life history pattern is characterized by early development in the oceanic
zone followed by later development in the neritic zone (Figure 9.1, middle panel).
The best-known example of this life history pattern is that of the loggerhead turtle
(for review, see Bolten, in press). Use of genetic markers has confirmed the relationships between oceanic foraging grounds and rookeries (Bowen et al., 1995;
Bolten et al., 1998) that had been hypothesized based on length–frequency distributions (Carr, 1986; Bolten et al., 1993) and tag returns (Bolten, in press). Although
based on rather few data (summarized in Carr, 1987a), this life history pattern is
thought to be the pattern for the green turtle, hawksbill ( Eretmochelys imbricata ),
and Kemp’s ridley ( Lepidochelys kempii [Collard and Ogren, 1990]). Little is known
about the ecology of juvenile olive ridleys ( Lepidochelys olivacea ); differences
among populations from different ocean basins suggest that this species exhibits
either a Type 2 or a Type 3 life history pattern, perhaps in response to differences
in resource availability. In the West Atlantic (Pritchard, 1976; Reichart, 1993; Bolten
and Bjorndal, unpublished data) and Australia (Harris, 1994), olive ridleys appear
to exhibit a Type 2 life history pattern, whereas East Pacific populations (Pitman,
1990) appear to exhibit a Type 3 life history pattern.
Following the hatchling swim-frenzy stage (Wyneken and Salmon, 1992), loggerheads have a transition period when the post-hatchling begins to feed and moves
from the neritic zone into the oceanic zone (Bolten, in press). The duration, movements, and distribution of the post-hatchlings during this transition have been
reviewed by Witherington (2002, in review a). This transition is relatively passive
1123 book.book Page 247 Monday, November 11, 2002 11:11 AM
247
Walker, 1994; Musick and Limpus, 1997). However, the size difference between
flatback turtles and those species exhibiting Type 2 or 3 patterns does not seem to
be great enough to make a significant difference with respect to marine predators.
The larger hatchling size of the flatback may be a response to terrestrial predators
and the need to survive the predator gauntlet from the nest to the water. The larger
size of flatback hatchlings allows them to escape some bird and crab predators on
Australian beaches that prey upon the green turtle ( C. mydas ) and loggerhead
hatchlings (Limpus, 1971). The fact that other sea turtle species have not also
responded to terrestrial predators by increasing hatchling body size suggests that
the selective pressures leading to the increased size of flatback hatchlings are not
fully understood. Knowledge of the selective advantages of large hatchling size may
be critical for understanding the success of the Type 1 life history pattern.
The early juvenile stage of Type 1 species (including post-hatchlings) probably
feeds on the surface and within the water column, and may later develop a benthic
feeding strategy once the turtle has gained buoyancy control and can dive to the
sea floor. In the shallow waters that Type 1 species inhabit, their foraging behavior
may be a mix of pelagic and benthic feeding throughout life. Support for this
mixed foraging strategy is seen in the diet of both small and large flatback turtles
(Limpus et al., 1988; Zangerl et al., 1988). However, the number of samples that
has been evaluated is too small to be conclusive; more studies on the diet of
flatbacks are needed.
9.3.2 T YPE 2: T HE O CEANIC –N ERITIC D EVELOPMENTAL P ATTERN
The Type 2 life history pattern is characterized by early development in the oceanic
zone followed by later development in the neritic zone (Figure 9.1, middle panel).
The best-known example of this life history pattern is that of the loggerhead turtle
(for review, see Bolten, in press). Use of genetic markers has confirmed the relationships between oceanic foraging grounds and rookeries (Bowen et al., 1995;
Bolten et al., 1998) that had been hypothesized based on length–frequency distributions (Carr, 1986; Bolten et al., 1993) and tag returns (Bolten, in press). Although
based on rather few data (summarized in Carr, 1987a), this life history pattern is
thought to be the pattern for the green turtle, hawksbill ( Eretmochelys imbricata ),
and Kemp’s ridley ( Lepidochelys kempii [Collard and Ogren, 1990]). Little is known
about the ecology of juvenile olive ridleys ( Lepidochelys olivacea ); differences
among populations from different ocean basins suggest that this species exhibits
either a Type 2 or a Type 3 life history pattern, perhaps in response to differences
in resource availability. In the West Atlantic (Pritchard, 1976; Reichart, 1993; Bolten
and Bjorndal, unpublished data) and Australia (Harris, 1994), olive ridleys appear
to exhibit a Type 2 life history pattern, whereas East Pacific populations (Pitman,
1990) appear to exhibit a Type 3 life history pattern.
Following the hatchling swim-frenzy stage (Wyneken and Salmon, 1992), loggerheads have a transition period when the post-hatchling begins to feed and moves
from the neritic zone into the oceanic zone (Bolten, in press). The duration, movements, and distribution of the post-hatchlings during this transition have been
reviewed by Witherington (2002, in review a). This transition is relatively passive
1123 book.book Page 247 Monday, November 11, 2002 11:11 AM