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Assessment of Sea-Turtle Status and Trends: Integrating Demography and Abundance
dependence in the somatic growth rate of immature green turtles in the Caribbean region. They found a negative correlation between population density and both the mean annual growth rate (as measured by carapace length) and an index of body condition. That suggests that Caribbean green turtles are food limited when abundance is high.
Bell et al. (2010) evaluated evidence of depensation in green turtles and loggerhead turtles. They focused on the relationship between rookery size (as measured by total clutches per season) and fertilization success, hatch success, and hatchling emergence success; they used data on the Cayman Islands and a meta-analysis of global data. The study found no evidence of depensation in either species in either the Cayman Islands data or the global data. However, because the analysis was based on a mixture of cross-sectional and time-series data, the result needs to be treated with caution. A more complete analysis would treat the data as multiple time series with depensation operating within, but not between, the component series.
A substantial proportion of the effort expended to collect sea-turtle data in the United States is invested in the Sea Turtle Stranding and Salvage Network (STSSN). Because the usefulness of the data generated in that program has been debated (Epperly et al., 1996; Turtle Expert Working Group, 2000), the committee addresses STSSN here in some detail. Sea-turtle strandings occur when animals have washed up on a beach or into shallow water. Stranded animals may be dead or dying because of anthropogenic causes, such as interactions with fisheries, or natural morbidity, such as disease or “cold stunning” when they have been exposed to lethal cold-water temperatures. Strandings include all life stages that are present in neritic habitats, including juveniles and adult males. Carcasses provide opportunities for data collection that are difficult or impossible with live animals, such as collection of data for evaluating maturational status and removal of the humeri for age and growth studies. Carcasses are checked for tags; this is an important source of tag recoveries that are used to evaluate growth and dispersal of individual turtles. Strandings can also provide some information on mortality and have been correlated with levels of fishing effort and enforcement (Lewison et al., 2003). With careful consideration of the many sources of variability that affect the probability of stranding and detection of carcasses, strandings may also provide distribution and trend information that is relevant to population assessment (Chaloupka et al., 2008b).
The density of strandings has been used as a trigger for management action in some areas and has resulted in spatial closures in fisheries