Gravid green turtles employ a mixed capital-income breeding strategy where food is abundant

Sea turtles are marine ectotherms commonly considered capital breeders that use accumulated energy stores for reproduction. In some green turtle Chelonia mydas populations, gravid females feed during the inter-nesting period, indicating that they are not exclusively capital breeders but may supplement energy stores with energy gained through feeding during inter-nesting periods. However, the significance of this feeding remains unknown, as does the time allocation between energy intake and energy-saving behaviors during inter-nesting periods. In this study, we deployed video, head-mounted acceleration, and GPS loggers on 9 green turtles nesting on Ishigaki Island, Japan, to monitor their feeding behavior during the inter-nesting period. We found that the turtles spent nearly half of the inter-nesting period resting (42.1% on average), but also dedicated 3.4% of their time to foraging, exhibiting a bimodal daily pattern with peaks in activity during the early morning and evening. Most feeding occurred around the algae/seagrass meadows in close vicinity to resting sites, so little energy is required to shuttle between feeding and resting sites. In such cases, the energy stores acquired prior to the breeding migration can be ‘topped up’ with feeding during inter-nesting intervals. Our results indicate that gravid green turtles employ a mixed capital-income breeding strategy in which females mostly rely on capital energy, but may supplement this with small amounts of income energy gained by feeding during inter-nesting periods.