Abstract
Sea turtles bask at the ocean surface, but little is known about the patterns and ecological context of surface behavior in the wild. This study investigated the surface behavior of ten juvenile loggerhead sea turtles (34 - 58 cm straight carapace length) satellite tagged in Madeira, in the pelagic eastern North Atlantic. During a total of 2273 tracking days, turtles moved through oceanic areas with a mean depth of ~3400 m. On average, turtles spent one third of the time at the surface (0 - 1 m depth), spending 43% of the time at the surface during the day and 29% of the time during the night. Generalized linear mixed modelling showed that the proportion of time at the surface was significantly larger during the day, particularly during spring and summer. Time spent at the surface during the day increased with elevated air temperatures and weak winds, probably to maximize the benefits of solar absorption. Conversely, the probability of being at the surface during the day decreased as horizontal search effort increased, suggesting a trade-off between basking and daytime foraging activities. At night, time spent at the surface was not associated with air temperature or wind speed but was instead positively associated with moon illumination. As turtles tend to dive deeper during clear nights, increased surface time may be needed to recover from deeper dives. This study presents important aspects of the behavioral ecology of the species during the oceanic juvenile phase. The findings reported here may be relevant for species management and conservation, including correction of census data and management of interactions with surface fishing gear and other anthropogenic activities.
Highlights
Basking is a frequent activity for most reptiles, exposing them to solar radiation
Animals faced a variety of environmental conditions, with wind speed ranging from 0.2 to 22 m s -1, air temperature of 7.0 to 26.8 °C and SST between 14.4 and 25.5 °C
Air temperature was highest during summer and fall, while wind speed was lowest during those seasons (Fig. S1)
Summary
Basking is a frequent activity for most reptiles, exposing them to solar radiation (see Zug et al, 2001). As well as the apparent benefits, basking behavior has associated costs. Time spent basking may reduce foraging time and increase exposure to predators (Heithaus and Frid, 2003; Huey and Slatkin, 1976). The pressure for other activities, such as foraging and predator avoidance, may offset the need for basking (Crawford et al, 1983). Basking behavior may represent a compromise between demands and benefits. Under low thermal quality conditions, such as winter or early morning, the costs of basking may outweigh its thermal benefits (Blouin-Demers and Nadeau, 2005; Crawford et al, 1983; Rowe et al, 2014)
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