First Documented Record of Nesting by the Olive Ridley Turtle (Lepidochelys olivacea) in Ecuador
ABSTRACT
We report on the first confirmed occurrence of Lepidochelys olivacea nesting in Ecuador based on the presence of eggshells and the identification of a late-stage embryo at a beach located in Manta (lat 0.94°S, long 80.7°W), Manabí Province, Ecuador, in October 2004. This is the second-most-southerly record of olive ridley nesting on the Pacific coast of South America.
Olive ridley turtles (Lepidochelys olivacea) occur in the 3 tropical oceans with the major nesting grounds and arribadas on mainland shores of the East Pacific and northeastern India. Arribadas occur at Nancite and Ostional, Costa Rica (Central America); Escobilla, Oaxaca, Mexico; and along the Orissa coast of India, originally at the Gahirmatha and Devi river mouths and subsequently at the Rushikulya River mouth in the Indian Ocean (Pritchard 1997, 2003; World Wildlife Fund 2004). Lesser nesting sites occur throughout the Pacific coast of Central and North America from Panama to Mexico as well as on tropical beaches throughout Southeast Asia (Pritchard 1997).
The US Endangered Species Act and The World Conservation Union (IUCN) categorize L. olivacea as endangered (IUCN 2006), and it is listed in Appendix I of the Convention on International Trade in Endangered Species of Flora and Fauna (Pritchard 1997). This species is one of the 4 or 5 species of sea turtles found in marine waters of Ecuador. Although nesting activity by leatherback turtles (Dermochelys coriacea), East Pacific green or black turtles (Chelonia mydas; also known as Chelonia agassizii), and hawksbill turtles (Eretmochelys imbricata) occurs along the continental Ecuadorian coast (Green and Ortiz-Crespo 1982) and, particularly for black turtles, in the Galápagos Islands (Green and Ortiz-Crespo 1982; Hurtado 1984; Zárate 2002; Zárate et al. 2006), olive ridleys have not been observed nesting either in mainland Ecuador or on the Galápagos (Green and Ortiz-Crespo 1982). Although olive ridleys are the most abundant sea turtle in continental Ecuador, they are seldom found in the Galápagos (Green, 1994). It is known that this species migrates to and forages in large numbers in marine waters of Ecuador (lat 3°S–2°N) 30–40 miles from the coast from December to May, after leaving Mexican and Central American nesting grounds (Hurtado 1981, 1987; National Marine Fisheries Service [NMFS] and US Fish and Wildlife Service [USFWS] 1998; Pritchard 2003). Indeed, this is also confirmed by the enormous concentration of olive ridleys registered by marine observers with the Inter-American Tropical Tuna Commission (IATTC) along lat 5°N and between long 100°W and 80°W during July–December, based on an data records analysis from 1990 to 2002 (IATTC 2004).
During the 1970s, vast numbers of olive ridleys (100,000 to 148,000 individuals/y) were slaughtered for consumption and for the leather market in Ecuador during the 1970s (Green and Ortiz-Crespo 1982; Carr 1984). Additionally, the composition of artisanal fishery landings due to by-catch of sea turtles is mostly represented in higher proportions by this particular species in Ecuador (Hurtado 1987; Alava 2000a). In the last decade, olive ridley mass mortality events, attributed to several causes, have also been reported on Ecuadorian beaches (Alava et al. 2002, 2005). Stranded turtles in 1994–1995 and in 1999 showed curved carapace length (CCL) mean of 65.9 cm (range: 53–78 cm) and 60.0 cm (range: 57–63 cm), respectively (Alava et al. 2005). Thus, Ecuadorian waters may be considered a key foraging ground for both adult and subadult olive ridleys (Carr, 1984). Herein, we report the first confirmed occurrence of reproduction by the olive ridley turtle found along the central Ecuadorian coast.
Nesting Location and Specimen Identification
In October 2004, a nest with ∼ 50 sea turtle eggshells and a single dead late-stage embryo were found at a beach (Playa Murciélago) near Manta (lat 0.94°S, long 80.7°W), Manabí Province, Ecuador (Fig. 1). This embryo had a total length of 4.0 cm, a CCL of 3.1 cm, and a curved carapace width of 2.8 cm. Photos were taken, and the hatchling was preserved with a solution of EtOH in fresh seawater. Remnants of the eggshell and the yolk sac were still attached, respectively (Fig. 2a, b). One of the authors (H. Valverde) looked for signs of nests, nesting tracks, or nesting females, but no further signs of nesting activity were detected in that area.
Citation: Chelonian Conservation and Biology 6, 2; 10.2744/1071-8443(2007)6[282:FDRONB]2.0.CO;2
Citation: Chelonian Conservation and Biology 6, 2; 10.2744/1071-8443(2007)6[282:FDRONB]2.0.CO;2
The specimen was initially identified as L. olivacea by H. Valverde and J.J. Alava following keys by Pritchard and Mortimer (1999) and Wyneken (2001). This idenfication was later confirmed by P. Pritchard and J. Wyneken. The identification criteria were head shape, lateral cephalic scalation, number of prefrontal scales, carapace scutes, and coloration (Fig. 2c). The head shape was triangular from above, showing 4 prefrontal scales (2 pairs). The specimen coloration was completely black both above and below, and the inframarginal scute number was found to be 4 pairs. Of particular interest was the number of coastal scutes in each side (n = 5), as well as vertebral scutes counted (n = 5) in this individual because hatchlings of this species usually show from 6 to 9 pairs or more than 6 lateral and vertebral scutes (Pritchard and Mortimer,1999; Wyneken 2001). However, 5 pairs can be sometimes depicted in this species (Pritchard and Mortimer 1999). Generally, the average number of eggs in olive ridley nests is around 110 (Miller 1997), but no other eggshells were found in that area.
Discussion
We considered the potential for misidentification of this specimen as a displaced Kemp's ridley (Lepidochelys kempii) or a very odd and displaced loggerhead turtle (Caretta caretta). Generally, it is difficult to establish differences between normal juveniles of L. kempii and L. olivacea (Pritchard 1997), apart from the coastal scute count. Kemp's ridley hatchlings are dark grey to grey-green in color and also have 5 lateral (4–6 is common) and 5 vertebral scutes (Wyneken 2001). However, at present, nests, hatchlings, and adults of Kemp's ridleys only occur at Rancho Nuevo, Tamaulipas, Mexico and Veracruz, Mexico; and south Texas and in marine waters of the Gulf of Mexico (Pritchard 1997; Pritchard and Mortimer 1999). According to Pritchard and Mortimer (1999), hatchlings of sea turtles can show high variation in the number and configuration of carapace scutes.
It is important to emphasize that our identification of this specimen as an olive ridley was also based on the assumption that it could only be a marine turtle species known from the eastern Pacific (e.g., excluding L. kempii), making the task primarily one of differentiating between L. olivacea and C. caretta. The fact that the specimen turned out to have just 5 pairs of costal scutes is important because this trait uncommon for L. olivacea from the East Pacific (about 30% of specimens) relative to its frequency in the Atlantic (P. Pritchard, pers. obs.).
At present, loggerheads have not been recorded in by-catch landings or on Ecuadorian beaches (Green and Ortiz-Crespo 1982; Hurtado 1987; Alava 2000b; Alava et al. 2005) even though a few individual specimens have been sighted in marine waters off Ecuador by trained marine observers aboard IATTC tuna purse-seine vessels (IATTC, 2004), or incidentally captured offshore during circle-hook experiments with artisanal fisheries (Largacha et al. 2004). Moreover, these observations of loggerheads are not yet confirmed in Ecuadorian marine waters. The loggerhead, in contrast to other marine turtles, is scarce in tropical areas (Pritchard 1997, 2003). More recently, this species has been found in the costal and offshore waters of Peru, as evidenced by turtles captured by artisanal fisheries, around lat 12°–20°S and long 80°–70°W (Kelez et al. 2003; Alfaro-Shigueto et al. 2004).
This is the first confirmed report of L. olivacea nesting in Ecuador. Previously, anecdotal comments from fishermen and media sources have mentioned the nesting of unidentified sea turtles in beaches adjacent or close to the following fisheries communities: Playa Bruja, Libertador Simon Bolívar, and Valdivia in Guayas Province (Fig. 1). However, no scientific evidence has been collected to support those remarks. During the mass mortality episodes in Ecuador (Alava et al. 2005), the carapace lengths of stranded olive ridleys on the Ecuadorian coast overlapped with lengths reported for nesting females (60–70 cm CCL) from the Pacific coasts of Mexico and Costa Rica (NMFS and USFS, 1998), although probable near-adult turtles (57.8–58.5 cm CCL) were also observed along the Ecuadorian coast (Alava et al. 2005). This indicates that olive ridley adults are sometimes present close to Ecuadorian beaches, and it is likely that they nest sporadically before or during the seasonal migration or foraging in marine waters of Ecuador.
Both large and diffuse aggregations of olive ridley turtles have been sighted by IATTC-observers off Colombian coast during April and May, and off the Peruvian coast during January and March (IATTC, 2004). Some L. olivacea costal bones were observed on Pinta Island, Galápagos, in October 2003, this being the first actual record for the Galápagos Islands (P. Pritchard, pers. obs.). Likewise, a stranded female individual, with severe injuries in both the skull and nuchal scute and still alive, was identified and rescued in Tortuga Bay (Santa Cruz Island, Galápagos) in March 2004 (P. Zárate, pers. comm.). This turtle was kept under intensive medical care in one of the labs of the Charles Darwin Research Station for 3 weeks; however, the animal died because of an internal septicemia. In addition to these records, 3 olive ridleys were observed during a by-catch assessment of pelagic long-lining (High Seas Experimental Plan) around the Galápagos Marine Reserve (Murillo et al. 2004).
In October 2006, 2 years after the initial encounter reported here, a second neonate of L. olivacea was found alive at the Bunche beach, Esmeralda Province, in northern Ecuador (P. Zárate, pers. comm., 2007). This field observation is the second hatchling recorded in Ecuador and it supports our finding on nesting activity by olive ridley turtles. To our knowledge the southernmost nesting record for L. olivacea along the American Pacific coast was in northern Peru, south of the Rio Tumbes (Hays-Brown and Brown 1982). Frazier and Salas (1983) hypothesized that, after migrating to Ecuadorian foraging grounds, it is probable that some nesting by olive ridleys may also occur in Ecuador. The neonate summarized in this paper, coupled with that reported by Zarate (pers. comm.), substantiates this theory.
Coastal zone of Ecuador showing the location of Manta Harbor in the Ecuadorian shoreline (black star) where a late-stage embryo was collected. Additional sites in the Guayas Province are indicated where olive ridely nests have been reported but not confirmed.
Late-stage embryo of an apparently normal specimen of L. olivacea; (a) remains of eggshell (light gray arrow), the chorioallantoic membrane (dark gray arrow) and the yolk sac (black arrow); (b) eggshell attached to the neonate body; (c) external features of the carapace showing central scutes (white arrows). (Photo by Harold Valverde.)
