SURVIVAL PROBABILITIES

One of the greatest gaps in developing the conceptual model is in estimates of survival of immature turtles and nesting females of all species. Survival of turtles through embryonic development to their emergence from the nests is discussed above (see the section “Fecundity”).

Adult Females

Estimates of survival for adult females have been derived from mark–recapture studies that used open robust design for hawksbills (Kendall and Bjorkland, 2001) and leatherbacks (Dutton et al., 2005). This analysis is the best available approach for estimating survival probabilities based on mark–recapture data on nesting beaches if sufficient data are available. Survival estimates have also been generated from recovery analyses (Campbell and Lagueux, 2005; Troëng and Chaloupka, 2007) and a model of remigration intervals (Solow et al., 2002). Applying more than one approach to a population can increase confidence if the independently derived estimates are similar. For green turtles nesting at Tortuguero, Costa Rica, four analyses that used three techniques yielded similar estimates of probabilities of annual survival of adult females (Solow et al., 2002; Campbell and Lagueux, 2005; Troëng and Chaloupka, 2007).

Despite multiple calls for new studies (see Table 1.2; Turtle Expert Working Group, 2000; Heppell et al., 2003), there have been few attempts to update estimates of survival of loggerhead turtles nesting in the United States with mark–recapture analysis (e.g., Hedges, 2007), and current models still rely on results from the 1970s when mark–recapture studies were conducted on Little Cumberland Island, Georgia (Richardson et al., 1978; Frazer, 1983). The survival rates from those studies were not estimated with the open robust-design methods that have been developed to account for detectability of nesting females (Kendall and Nichols, 2002) but did account for tag loss. Efforts to assess loggerhead status and interpret trends in nests with lifecycle and simulation models have been stymied by the lack of new estimates (Turtle Expert Working Group, 2000; National Marine Fisheries Service Southeast Fisheries Science Center, 2001). That has also prevented proper evaluation of the effectiveness of management actions, such as the implementation of turtle excluder devices (Epperly and Teas, 2002).

Survival of nesting female Kemp’s ridley (Lepidochelys kempii) turtles was estimated in a model-fitting exercise in which a simple age-structured model was fitted to nest census counts from Mexico to obtain a point estimate of annual survival before and after 1990 (Turtle Expert Working Group, 2000; Heppell et al., 2005). That was a unique circumstance in that all nesting of this highly endangered species was restricted largely



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