Long dive capacity of olive ridley turtles (Lepidochelys olivacea) at high water temperature during the post-nesting foraging period in the Arafura Sea

Abstract Water temperature and body size are considered to be important factors influencing the diving capabilities of ectothermic reptiles. Although high water temperature and small body size tend to cause short dive durations, previous studies have reported that olive ridley turtles , the smallest sea turtle species distributed in tropical regions, often conduct prolonged dives. To understand diving behavior during the post-nesting foraging periods, especially the relationship between dive duration and water temperature for this species, satellite relay data loggers were attached to 10 nesting females (straight carapace length: 60.5 ± 2.6 cm, estimated body mass: 30.5 ± 4.0 kg) in West Papua, Indonesia, in 2017 and 2019. During the post-nesting tracking period (34–153 days), the turtles migrated southward to the Arafura Sea. A total of 9469 dives were observed, and 28.9% of the dives were longer than 1 h (mean: 44.0 ± 33.1 min, max: 220 min), although the turtles experienced high water temperatures (25.5 ± 2.6 °C). The behavioral aerobic dive limits (behavioral ADLs) calculated from the relationship between the dive depth and duration of olive ridley turtles were 89.6 min and 167.7 min for V-shaped and U-shaped dives, respectively. Even for dives above the behavioral ADL (1.8% for V-shaped and 2.0% for U-shaped dives), the turtles dove 1.1 ± 0.1 (max: 1.6) and 1.1 ± 0.1 (max: 1.3) times longer than the behavioral ADLs for V-shaped and U-shaped dives, respectively. On the other hand, the calculated ADLs (cADLs), estimated from the metabolic rates and oxygen stores of loggerhead turtles, were 51.2 ± 20.3 min (range: 24.1–139.3 min) and 99.8 ± 38.5 min (range: 39.4–258.3 min) for V-shaped and U-shaped dives, respectively. The turtles often exceeded the cADLs (21.4–29.1% for V-shaped dives and 21.2–42.2% for U-shaped dives), and they dove 1.4 ± 0.3 (max: 3.1) and 1.3 ± 0.3 (max: 3.4) times longer than the cADLs for V-shaped and U-shaped dives, respectively. However, those long dives were not considered anaerobic because of the short post-dive surface durations (4.7 ± 5.8 min). Additionally, the relationship between dive duration and water temperature indicated that olive ridley turtles dove longer than loggerhead and green turtles in the high temperature range (> 20 °C). This study confirms that the diving capacity of olive ridley turtles is qualitatively different from those of loggerhead and green turtles for several reasons, such as low metabolic rates and/or low activity levels at high water temperatures.