Map of study beaches on the US Naval Station at Guantanamo Bay. Inset map shows Cuba. 

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... — Sea Turtle Nesting Habitat at Guantanamo Bay, Cuba disturbances such as concrete and artificial lighting. Removing these disturbances may entice hawksbills to nest near that vegetation. Despite model differences, we agree with the experts that vegetation deserves a high weight on GTMO. Other studies at GTMO tested the idea that sampling a larger number of nesting beaches less frequently might improve the validity of the results. In a technical report to GTMO, we examined observations of 33 zones over 10 beaches (Fig. 1) collected at an annual time-step, and we also collected environmental data for the 33 zones in April of 2001 (Alberts et al. 2001). However, we did not find that variance in this observational dataset was explained by the environmental data to a reasonable degree. The infrequent temporal sampling of the observations in the annual dataset likely produced errors of omission, because turtle nesting evidence can be erased with weather or human traffic throughout the year. Together, results of Alberts et al. (2001) and this study reinforce the need for weekly sampling over a larger study area on GTMO. Because nesting preferences within the GTMO site cannot be predicted based solely on the environmental variables collected during this study, we suggest that nest site fidelity plays a role. To test this hypothesis, a larger study area and longer study period is required. GTMO authorities should allow volunteer access for sea turtle observations at all beaches at least once a week for at least 8 consecutive years. Experts suggest 8 years of nest observations can be used to estimate population totals and long-term data are critical for studying population trends. Those data may allow the construction of an HSI model that would more accurately predict nest densities at GTMO, and perhaps be robust enough to use at other sites in the Caribbean. Based on our results, compaction levels of the substrate on GTMO’s beaches should not be altered, for example, with additional construction, beach nourishment, or heavy equipment (USFWS 1999). Vehicular traffic should be prohibited on beaches because it compacts sand alters the beach slope, and could crush nests that are not roped off. Artificial illuminance is a negative influence on nesting habitat. At the time of this study, on most GTMO beaches nighttime lighting (e.g., volley ball courts, cabana lights, and parking lot lights) was minimized when beaches were not in use. This regulation should be expanded to all beaches throughout the year, and enforced. Eliminating or controlling light pollution (see Witherington 2000) on all beaches throughout the year may encourage females to return to otherwise suitable nesting sites. Man-made obstacles are a threat to habitat, and additional beach development should be prohibited. Because percentage of sand was important in the model, the substrate should not be amended with soils or sand, nor should sand be removed. Although the vegetation variable was not included in the models, planting more trees on beaches such as Pebble has been recommended to increase HS for hawksbills (Alberts et al. 2001). The role of the percentage of debris in the model contradicted expert opinion, suggesting that more studies on how debris affects nesting habitat at GTMO would be useful. Since 2001, new development on GTMO has reportedly not affected sea turtle habitat or nesting. Steps to protect turtle habitat since 2001 include activities such as education and outreach and an improved bollard-and- cable system to keep vehicles off the beaches around known nesting areas. Morrison et al. (1992) stated, ‘‘ In general, most HSI or habitat models can be expected to account for roughly half the variation in species density or abundance. On-site environmental conditions generally account for even less variation in population density when migratory species are considered. ’’ Indeed, our models successfully classified 40% of the zones. Therefore, these models may be used for the theoretical purpose of exploring relationships between environmental variables and HS. The modeling process can help shape future habitat studies, and places GTMO in the context of the literature on sea turtle nesting patterns in the wider Caribbean. However, none of the HSI models did extremely well in predicting observed HS classes, implying that influences beyond these environmental variables, such as nest site fidelity, may contribute to HS. In addition, small sample size, a common issue for endangered species datasets, may have contributed to poor model performance. Continued weekly monitoring will be needed at GTMO in order to make sound management decisions. Many studies on endangered species, such as this one, are forced to use small opportunistic datasets and low-cost rapid environmental assessment methods. Short studies complicate management decisions, especially for species like sea turtles with long maturation periods (ca. 20 years), long lives (ca. 100 years), migratory habits, and demon- strated nest site fidelity. For example, on a beach where poaching began in the 1920s, the females may continue to nest on their natal beach until the last one dies in the year 2000 (Magnuson 1990). Similarly, today’s nesting ...

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... and conservation efforts that focus on nesting habitats are needed to ensure the survival of endangered sea turtle populations (Lutz and Musick 1997; Klemens 2000; Witherington 2000). Species observed nesting at the US Naval Station at Guantanamo Bay, Cuba (GTMO) ( Fig. 1) include greens ( Chelonia mydas ) and hawksbills ( Eretmochelys imbricata ). Hawksbills are classified as critically endangered (IUCN 2006) and greens as endangered (Seminoff 2004) by the World Conservation Union. The Convention on International Trade in Endangered Species of Wild Fauna and Flora prohibits commerce of sea turtle products for participating nations. The US Endangered Species Act of 1973 lists sea turtles as endangered, and the National Environmental Protection Act of 1969 requires the conservation of sea turtles and their habitat by federal agencies such as the US Navy. Sea turtle populations are often monitored on nesting beaches because they can exhibit relatively strong nest site fidelity by returning to their natal beaches or previous nesting sites (Bjorndal 1995). We considered the greens and hawksbills observed nesting on GTMO as populations unique to the military base. Nesting seasons vary widely among sea turtle species in terms of frequency and timing; most Caribbean species nest every 2 to 3 years from March through September (M ́rquez 1990). Several nests of eggs may be laid each season. Hawksbills average 2.3 nests per season (M ́rquez 1990), and greens tend to nest 2 to 3 times per season (Carr et al. 1978). Females reach sexual maturity at around 15 to 20 years (Bjorndal 1995), and have average lifespans of 50 to 100 years; sea turtles are relatively long- lived compared with other vertebrates (Klemens ...

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... (HS). In models with multiple variables, the weighted composite index (CI) is a weighted arithmetic mean (or the geometric mean in cases with limiting variables such as food sources) of all the SIs, again with a range from 0.0 to 1.0 (USFWS 1981; Stoms and Estes 1993). In a regression HSI model approach, linear least squares regression is used to relate environmental variables to variation in the abundance or density of the target species. The results are normalized by the maximum observed density to produce an HSI score between 0.0 (unsuitable) and 1.0 (optimal). In addition to the CI and regression methods, our study employed a third approach, which is a combination of the two. In this ‘‘ combined ’’ model, coefficients from the regression HSI model are used to weight the relative importance of the variables, which are represented by SI scores (0.0–1.0). This approach is essentially the same as the expert-weighted component index model, except that the weights are the standardized regression coefficients from the regression approach. This empirical approach eliminates the need for expert opinion to determine the relative weights of variables and can lead to more site- specific models with higher predictive accuracy (Morrison et al. 1992). The final scores are, again, CIs ranging from 0.0 (unsuitable) to 1.0 (optimal). In this study, we compared the performance of 3 HSI model-building approaches for the GTMO site. An HSI score for each area was computed using 1) suitability indices with expert weights, 2) unscaled environmental variables with regression-based weights, and 3) suitability indices with regression-based weights. We tested the ability of each model to predict observed HS classes (low, medium low, medium high, and high) and the ability to rank areas relative to others in terms of observed nest density (ND) (1–15). Based on the most accurate HSI model-building approach, we then explored the relative importance of individual environmental variables as indicators of nesting HS. For many HS studies, ND is assumed to represent HS (USFWS 1981). An observed nest attempt, or a body pit in the sand, was the unit of measurement for this study. From the dataset we were not able to distinguish ‘‘ false ’’ nests, or abandoned nesting attempts, from successful nests, nor could we have attributed false nesting to poor environmental conditions vs. other disturbances such as predators. Our study’s criterion for suitable habitat was essentially female nest site preference, so regardless of whether eggs were laid or not, if a female attempted to dig a nest, this site was interpreted as ‘‘ suitable. ’’ Resident volunteers on GTMO recorded nest attempts from 1999 to 2001 for Windmill, Kittery, Cable, and Pebble beaches (Fig. 1). The beaches were partitioned into 15 50-m-wide zones following methods from other sea turtle habitat studies (Loop et al. 1995) (for example, see Fig. 2). Over the 2.5 years, a reasonable temporal window for a typical 2- to 3-year nesting cycle, observations of fresh sea turtle nests were collected at a time-step ranging from 2 to 30 days. Volunteers recorded a total of 318 fresh turtle nests by walking an entire beach in the ...