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Assessment of Sea-Turtle Status and Trends: Integrating Demography and Abundance
will die soon after because of injuries caused by hooks or line entanglement (Lewison et al., 2004). However, there are few reliable estimates of post-release mortality in sea-turtle species despite their being essential for risk assessment and hazard mitigation. Chaloupka et al. (2004a) and Sasso and Epperly (2007) used satellite telemetry to estimate post-hooking mortality in loggerhead sea turtles but pointed out limitations of the method, including inadequate sample sizes and premature release of satellite tags, that make it difficult to derive reliable cause-specific mortality estimates.
Movement of Adult Females Between Rookeries
To date, all measured probabilities of female movements between rookeries are too low to influence management plans. Nesting females are highly philopatric (i.e., they return to their birthplace), but the degree of site specificity varies among species. Loggerhead nesting populations may show population structure (mitochondrial DNA differentiation) on a scale of less than 100 km (Bowen et al., 2005), green turtles on a scale of 500 km (Dethmers et al., 2006), and olive ridley (Lepidochelys olivacea) and leatherback turtles on a scale of more than 500 km (Lopez-Castro and Rocha-Olivares, 2005; Dutton et al., 2007). That information is important because the degree of site specificity and the scale of population structure determine the appropriate sizes of management units (see Chapter 2) and determine the extent to which nesting populations will reinforce each other.
Those geographic scales are supported in some species by tag-recapture data from renesting females. However, long-distance relocations of nesting females (beyond the geographic ranges outlined above) have been documented. LeBuff (1974) reported a loggerhead female relocating from southwest Florida to southeast Florida, and at least two tagged females have switched from Tortuguero to other locations in the Caribbean (citations in Bowen et al., 1992). A low level of switching between nesting sites is beneficial and probably necessary for the long-term persistence of sea-turtle species. In view of epochal changes in climate, oceanography, and geography, the appropriate nesting sites of, for example, the Pliocene are not the same as the ones today. Shifting among nesting beaches allows sea turtles to respond to a changing world.
Dispersal of Immature Sea Turtles
Immature sea turtles generally undergo two phases of dispersal (both of which are poorly understood): (1) hatchlings disperse away from the