Intraspecific behavioral dynamics in a green turtle Chelonia mydas foraging aggregation

We used animal-borne video footage to investigate the intraspecific behavioral dynamics of a green turtle Chelonia mydas foraging aggregation in Shark Bay, Western Australia, and test the hypothesis that the limited availability of a valuable habitat type promotes interference competition for access to these spaces. In 301 h of footage from 93 individuals, we recorded 176 turtle encounters involving between 1 and 7 turtles per encounter. The majority of encounters (55%) occurred in rare structurally complex benthic habitat (e.g. rock ledges) in deeper areas of this shallow sand-seagrass ecosystem, despite turtles spending only ca. 5% of their time at these sites. We recorded a suite of interactive behaviors nested within 3 encounter classes, which also showed habitat associations. Specifically, behaviorally diverse strongly interactive/social encounters, which represented 68% of total encounter time, occurred exclusively in structured areas. Turtle activities in these areas included solitary and group resting, self-cleaning (i.e. rubbing on hard surfaces), symbiotic cleaning by fish and other interactive behaviors including competitive contests. Competitive contests were 7 times more frequent in structured versus unstructured habitat, although turtle sightings were only twice as frequent in structured areas. In contrast, encounters in shallow habitat (e.g. seagrass beds) tended to be brief and involve limited interaction between solitary turtles. Interference competition at resting/refuge/cleaning sites could have a variety of important ecological implications, and a fuller understanding of chelonid sea turtle foraging ground behavioral ecology and habitat use (e.g. predictive habitat mapping) may require detailed knowledge of key non-foraging habitats.