MTN 140:6-8 Occasional Leatherback Turtle (Dermochelys coriacea) Nests: First Records in São Paulo State, Southeastern Brazil

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Occasional Leatherback Turtle (Dermochelys coriacea) Nests: First Records in São Paulo State, Southeastern Brazil

Daiana P. Bezerra^1,2, Ana Cristina V. Bondioli¹, Ana Paula S. Maistro¹ & Mariana B. Ebert¹
¹Instituto de Pesquisas Cananéia [IPeC], R. Tristão Lobo, 199, Centro, Cananeia, São Paulo, 11990-000, Brazil (E-mail: daiana.proencabezerra@gmail.com);
²Universidade Federal do Paraná [UFPR] - Programa Pós-Graduação em Ecologia e Conservação - Centro Politécnico, Curitiba, Paraná, Brazil

The leatherback turtle (Dermochelys coriacea), the largest species of turtle, is the only current member of the family Dermochelyidae residing in the world’s oceans (Pritchard 1996). These animals were formally classified globally as Critically Endangered and some populations have suffered drastic declines (IUCN 2012), due to factors such as illegal egg collection and incidental capture by industrial fisheries (Fiedler et al. 2012; Giffoni et al. 2008; Wallace et al. 2004) . In the 1980s, the global leatherback population estimate was 115,000 adult females with the Mexican population comprising 60% of this total (Spotila et al. 1996). Martinez et al. (2007) provided a new estimate of 30,000 adult individuals, nearly a 78% reduction from the previous estimate in less than a generation. However, the current status is Vulnerable (IUCN 2013) with the current global populations size estimate at 23,255 - 32,557 adult females, which is a conservative value as the largest populations could not be included in the assessment.

In Brazil, the regular nesting sites for leatherback turtles are located on the northern coast of the state of Espírito Santo (19°33.340'S; 39°46.312'W). This population has increased in the number of nests, from six nests recorded in 1992/93, to 92 nests observed in the 2003/04 season (Thomé et al. 2007).

Here we report on a single nesting occurrence of Dermochelys coriacea in Ilha Comprida, along the southern coast of the state of São Paulo (24°52.018’S; 47°45.420’W). In this region, Projeto Tartarugas of the Instituto de Pesquisas Cananéia (IPeC) has been in operation since 2003, with the purpose of the research and conservation of the five sea turtle species that occur along the Brazilian coast.

Between December 2012 and January 2013, the local community and tourists reported to Projeto Tartarugas that a leatherback turtle was observed possibly nesting on Ilha Comprida ́s beaches. According to the reports, the female was seen crawling out of the ocean four times. The first two records occurred on 19 December (only the date was given by the local community and fishermen) and 31 December 2012 (information and photographs were given by the local community and tourists) at Barra Nova and Ubatuba beaches, respectively. Despite our attempts, we could not confirm the presence of eggs where the nesting events were reported. The other two records occurred on 5 January at Ancoradouro Beach (nest I: 24o52.965’S, 47°44.125’W) and 12 January at Ubatuba Beach (nest II: 24°59.290’S, 47°51.258’W). These nests were confirmed by photographs of the animal, and we successfully located the clutches of incubating eggs (Fig.1A and 1B). Plastic mesh was placed above the nests to deter predators, according to Ficetola (2008). After 45 days of incubation, weekly monitoring surveys were conducted. The nesting season of D. coriacea in Brazil typically occurs between October and February, with an incubation period ranging from 60 to 78 days with each nest having an average of 87 eggs (Thomé et al. 2007). In nest I, 125 eggs were recorded and there were 106 eggs in nest II (including yolkless eggs - see below). The average depth of a leatherback egg chamber is 0.7 m - 1.0 m (Wallace et al. 2004), but the nests in this instance were 0.50 m (nest I) and 0.62 m (nest II) deep, with an average depth of 0.56 m.

Figure 1. Leatherback turtle nest in southeastern Brazil: A) leatherback turtle returning to the ocean after nesting; B) opening of the nest II; C) nest I flooded in salt water; D) yolked and yolkless eggs found in nest I.

No evidence of hatching emergence was observed through incubation days 82 and 75 for nests I and II respectively, so the nests were excavated to examine the eggs. We verified that the egg shells were intact, however internally the embryos were already decomposing. We observed that nest I had been inundated and the eggs were soaked in salt water (Fig. 1C). There were no signs of disturbance by animal or humans at the nest sites.

The majority of the eggs (nest I - 94.3%; nest II – 96.2%) had an average diameter of 6 cm, but some eggs were smaller, being approximately 2 - 3 cm in diameter (Fig. 1D). Dermochelys coriacea presents a number of yolkless eggs among normal eggs in the nests (Frazier & Salas 1984; Pritchard 1971). Thomé et al. (2007) indicated that 19.6% of the eggs inside nests were yolkless eggs. We found a smaller percentage of yolkless eggs: 5.7% in nest I and 3.8% in nest II.

The southern coast of the state of São Paulo is part of a migratory corridor used by leatherbacks to move between feeding and mating grounds (Fallabrino et al. 2010). Occasional nests have also been recorded in the states of Rio de Janeiro, Paraná, Santa Catarina and Rio Grande do Sul (Barata & Fabiano 2002; Soto et al. 1997). Occasional nests, as described in this study, are laid for unknown reasons. Some potential explanations may include physiological and/ or environmental conditions, or they may simply be the result of a lapse in navigational skills of female leatherbacks that leads them to randomly choose a beach along their migratory route (Barata & Fabiano 2002).

Despite the increase in nesting in Brazil, the situation of this species remains severe in the region. Successful conservation efforts for leatherback turtles must include protection of the nesting beaches and mitigation of threats in foraging areas and along migratory routes. The record of an unusual leatherback turtle nesting is important for expanding our knowledge of species biology thus contributing to leatherback conservation. Monitoring of this region will continue during the next breeding season to record the presence nesting females that may be using this region.

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