Strategic nest site selection in one of the world's largest loggerhead turtle nesting colonies, on Maio Island, Cabo Verde

Abstract

For species without parental care, such as sea turtles, nest site selection is particularly important for embryo development, hatchling survival and, ultimately, reproductive success. We conducted an 8-year (2012–2019) capture–mark–recapture study of the re-nesting behaviour of loggerhead turtles Caretta caretta to identify both inter- and intra-beach patterns of nest site selection. Our study site, Maio Island in the archipelago of Cabo Verde, hosts one of the largest loggerhead turtle nesting colonies globally. Of 1,060 females analysed, 77% laid repeated clutches within 15 km of their previous nesting sites both between and within nesting seasons. This site fidelity was particularly high (64–71%) for turtles nesting on the east coast of Maio Island. In two areas of the island (north-west and south-east) individual nesting zone consistency was extremely low (10–25%). In all cases extra-zone re-nesting events mainly occurred on the east coast. We also found that females avoided re-nesting near the shoreline, which is particularly relevant in the context of rising sea levels. Overall, loggerhead turtles nesting in Maio Island are philopatric but are using a bet-edging strategy to distribute nests amongst several beaches, choosing the safest area within each beach to maximize their reproductive success. This study highlights the priority sites for protection on Maio Island and could help to optimize capture–mark–recapture programmes. The data reveal the potential for adaptive responses to projected sea level rises.

Impact of Intrabeach Incubation Substrate Variability on Sea Turtle Reproductive Success

“…The effect of intrabeach variation in substrate type on reproductive traits of sea turtles is still relatively unexplored, although it may affect functionally important traits of offspring, such as size and vitality. The results found here for loggerheads demonstrate variability in embryonic development, hatching success, and hatchling phenotype as a function of intrabeach variation in the incubation substrate, all of which are indicative parameters of reproductive success (see also Patino-Martinez et al 2022b).…”

“…Correlations between incubation substrate types and hatchling phenotypes have been documented in recent years with interspecific (Saito et al 2019; Suhaimi et al 2020) and interbeach (Fadini et al 2011; Tacchi et al 2019) analysis, either in situ or under experimental conditions (Patino-Martinez et al 2022b). These results provide one of the few examples to date of intrabeach correlation between substrate type and reproductive success.…”

“…Their primary connection to the terrestrial environment is the sandy beaches used for nesting (Ackerman 1980; Miller 1997). Adult females exhibit natal philopatry, returning to their natal areas and choosing the same beach or nearby beaches to lay their eggs (Hulin and Guillon 2007; Stiebens et al 2013; Brothers and Lohmann 2015; Clusa et al 2018; Patino-Martinez et al 2022a). Because the eggs do not receive parental care, nest site selection plays a crucial role in determining environmental conditions for incubation (Miller et al 2003).…”

“…As clutch survival may vary according to substrate type, e.g., light sand beaches of biogenic origin have higher hatching success than dark beaches of volcanic origin and higher absorbance (Patino-Martínez et al 2022b), nest site selection can determine the survival of nests (Hawkes et al 2010; Patrício et al 2018). The effect of nesting substrate heterogeneity on sea turtle reproductive success has been studied comparing beaches (Mortimer 1990; Fadini et al 2011), colonies (Marco et al 2017; Saito et al 2019; Tacchi et al 2019; Patino-Martinez et al 2022b), and species (Saito et al 2019; Suhaimi et al 2020). However, this study examines, for the first time, the possible effect of intrabeach variation in incubation substrate on nest success and fitness of loggerhead turtle hatchlings.…”

Putting communities at the heart of marine conservation

“…Similarly, in Cabo Verde, the Maio Biodiversity Foundation is empowering local communities to improve protection of nearshore waters and threatened species through several means, including the Guardians of the Sea—a group of local fishers who monitor and record infractions in their fishing grounds—and a beach patrol programme monitoring sea turtle nesting in coastal villages around Maio Island that is fully integrated into coastal communities (Dutra & Koenen, 2014). This work has resulted in a 75% reduction in the poaching of nesting females, and has positioned Maio Island as a globally important refuge for the Vulnerable loggerhead sea turtle (Patino-Martinez et al, 2022) and one of the largest nesting colonies (Patino-Martinez et al, 2023). Finally, in Turkey, local NGO Akdeniz Koruma Derneği has developed community-based management for six no-take zones in the Gökova Bay marine protected area, resulting in a significant increase in fish biomass, and has successfully trialled a novel conservation approach for the Endangered Mediterranean monk seal, constructing an artificial ledge in a cave to provide critical pupping and resting habitat (Saydam et al, 2023).…”