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Chelonia mydas is distributed along the west coast of the American Continent, in Eastern Pacific waters, from Baja California (Eguchi et al. 2010; Macdonald et al. 2012) to Chile (Guerra-Correa, 2007; Quiñones et al. 2010), including the Revillagigedo Islands (Juarez-Ceron et al. 2002) and Galapagos Islands (Green 1984). Major rookeries in Mexico are found in Michoacán (Raygadas-Torres & Delgado-Trejo 2008) and the Islas Revillagigedo Archipelago (Awbrey 1984; Juarez-Ceron et al. 2002; Holroyd & Trefry 2010). In the Eastern Pacific, two major rookeries have been described; the Galapagos Islands (Green 1984; Zarate et al. 2002) and the Pacific coast of Costa Rica at Cabuyal (Santidrián Tomillo et al. 2014), Isla San José beaches (Fonseca et al. 2014) and Nombre de Jesús beach. Recently, Fonseca et al. (2018) indicated that San José Island is the most important nesting site for Pacific green sea turtles in Central America.

Hermosa Beach is located on the south Pacific coast of Costa Rica, in the canton of Osa, in the northern sector of the Osa Conservation Area (9.182243°N, 83.76671°W). The site is located between the Ballena Marine National Park (PNMB) to the south and Puerto Nuevo Beach to the north. Hermosa Beach currently is 5.88 km long (Fig. 1). It is characterized by having moderate to heavy rainfall, with an annual rainy season between 3000-3500 mm, and a dry season from December to March. Average temperatures range from 23-27°C (Alvarado et al. 2005).

Figure 1. Map of Costa Rica and location of Hermosa Beach, Uvita de Osa. Inset map is of Hermosa Beach showing the location of Chelonia mydas nest locations.

Sea turtle nest monitoring efforts began at Hermosa Beach in August 2020. No conservation research related to sea turtles had been undertaken on this beach before this date. Monitoring efforts consisted of walking the beach four days per week, starting at 05:00 h. The entire length of beach, from Punta Achiote in north to the Morete River in the south, was surveyed for nesting activity once per patrol. Morning surveys were led by a variety of individuals, including Reserva Playa Tortuga staff, lifeguards, local volunteers, and PNMB Rangers.

Nesting activity by a single green turtle was documented twice in December 2020. The turtle first laid 77 eggs on 06 December, then 26 days later on 31 December laid 82 eggs 100 m south of the first nest. Eggs from both nests were collected in a clean, disinfected bucket and transferred to the Reserva Playa Tortuga hatchery. During the first encounter, the female was making the body pit (9.191525°N, 83.777323°W; see title page).

The curved carapace length measured notch to notch was 86.6 cm and the curved carapace width measured 84.5 cm. Once the turtle finished the first nesting process, a metal tag was attached to the trailing edge of each front flipper, with the following codes: TGD0623 (right flipper) and TGD0622 (left flipper; Fig. 2).

Figure 2. Metal tag on the left front flipper of Chelonia mydas.

Although green sea turtle nesting in Pacific Costa Rica has been documented since the late 1970s (Cornelius 1982), there is still much to learn about the species nesting preferences in the country. Chacón et al. (2007) indicated that the nesting period for C. mydas in the Pacific coast of Costa Rica lasts from September to March. There have been a few recent publications relating to green turtle nesting in the northwestern province of Guanacaste (Blanco et al. 2012b; Santidrián Tomillo et al. 2014). Fonseca et al. (2018) reported a nesting population of East Pacific green turtles in northwest Costa Rica at San José Island, Murciélago Archipelago. They observed year-round nesting; the lowest nest totals were observed in May and highest nesting occurred from November to February, with a distinct peak in January. On the Osa Peninsula, nesting has been described from July to December. (Govan 1998; Barquero-Edge 2013). Our report of a nesting green turtle at Hermosa Beach coincides with the nesting pattern observed in northwestern Costa Rica, but more efforts are needed to determine the temporal distribution of nesting on Hermosa Beach.

Long term conservation efforts have shown a positive impact in the nesting population trend of the green turtle nesting on the Caribbean coast of Costa Rica (Troëng & Rankin 2004). The continuity of monitoring nesting beaches is key to understanding the use of habitat, the seasonality and periodicity of nesting. Knowing the temporal and spatial distribution of nesting is important for establishing timely management measures and advising monitoring and conservation efforts. Finally, the participation of the community is essential in order to maintain the monitoring program. Without community support, the information needed to manage and conserve green sea turtles would not exist.

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