Individual variation in feeding habitat use by adult female green sea turtles (Chelonia mydas): are they obligately neritic herbivores?

Abstract

Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28-42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.

Feeding ecology of the green turtle Chelonia mydas in northern Peru

“…Bays along the coast offer protection and food resources for juvenile green turtles (Hatase et al, 2006;Vander et al, 2013). Sechura Bay and Paracas Bay are two areas identified in past studies as green turtle foraging areas (De Paz & Alfaro-Shigueto, 2008;Santillán, 2008;Cáceres et al, 2013).…”

Spatial Distribution and Residency of Green and Loggerhead Sea Turtles Using Coastal Reef Habitats in Southern Mozambique

“…While they reported a weak correlation between bathymetry and relative abundance, where animals were more abundant when a steep change in depth contour occurred (Sleeman et al, 2007), depth was not a significant predictor in our study. The low total variance explained by our model may have been influenced by the multi-specific nature of our analysis (sightings of two turtle species merged), or a high degree of independent behavior exhibited by turtles, as has been demonstrated from satellite tagged turtles (e.g., Papi et al, 1997;Hatase et al, 2002Hatase et al, , 2006. Using models to predict and explain the distribution of marine megafauna and how it correlates with oceanographic or bathymetric variables is difficult (Polovina et al, 2004;Piatt et al, 2006;Sleeman et al, 2007).…”

Shorter telomere length with age in the loggerhead turtle: a new hope for live sea turtle age estimation

“…For example, although size-related differences in the use of feeding habitats (neritic vs. oceanic) by adult female loggerhead turtles have been reported within several populations (Hatase et al, 2002(Hatase et al, , 2007Hawkes et al, 2006), the mechanisms that produce and maintain this phenomenon are still unknown. Relative age information obtained with this method may become a key to help solve this phenomenon, which is closely related to facultative habitat shifts during ontogeny and alternative life histories in animals (Hatase et al, 2006;McClellan and Read, 2007). …”