models describe the probability of misidentifying previously counted turtles as new ones (Rivalan et al., 2005a). Although that identification error can be factored into models by using reobservation rates of nesting females, technological advances in tag persistence (e.g., PIT tags) have allowed the reduction of this error to insignificant rates.
Because counts made on nesting beaches depend on nesting activity, information on reproductive rates is required if these data are to be used for estimating the abundance of mature females. Reproductive rates often come from more completely monitored nesting beaches, but clutch frequency has recently been determined on the basis of interpretation of satellite transmitter locations (Tucker, 2010). Track counts have the greatest data requirements for estimating mature-female abundance, and counts of nesting females have the fewest data requirements. In each type of annual count, abundance estimates must account for nesting females that skip breeding seasons, which is a common trait in sea turtles. Horwitz–Thompson estimators can allow for the effect of skipped breeding on detection (Dutton et al., 2005) and have provided abundance estimates based on nesting-female counts over multiple nesting seasons. Modeling abundance on the basis of the identification of nesting females requires minimal additional data on reproductive rates because these rates can be measured as part of the method. Identification of nesting females over multiple nesting seasons can also contribute to modeling of mark–recapture rates. Open robust-design modeling using mark–recapture data has provided highly reliable nesting-female abundance estimates and detection probabilities and estimated rates of recruitment, survival, and breeding (Kendall and Bjorkland, 2001; Dutton et al., 2005; Rivalan et al., 2005b; Troëng and Chaloupka, 2007).
Data-collection techniques to measure abundance and other demographic characters of sea turtles in the water vary widely in many of the ways that nesting-beach techniques do. Like authors who report counts and other demographic data collected on nesting beaches, those who report similar data on sea turtles in the water seldom provide detailed justifications but often describe the techniques as appropriate for the conditions. The conditions vary with behavior that is specific to a species or life stage, water depth and clarity, currents and sea state, accessibility of habitat, availability of personnel and equipment, and funding. Some of the efforts continue with standardized methods that have been used historically to assemble comparable datasets.
Incentives to collect demographic information on sea turtles in the