Diel patterns in three-dimensional use of space by sea snakes

Abstract

Background: The study of animal movement and use of space have traditionally focused on horizontal and vertical movements separately. However, this may limit the interpretation of results of such behaviours in a three-dimensional environment. Here we use passive acoustic telemetry to visualise and define the three-dimensional use of space by two species of sea snake [Hydrophis (Lapemis) curtus; and Hydrophis elegans] within a coastal embayment and identify changes in how they use space over a diel cycle. Results: Monitored snakes exhibited a clear diel pattern in their use of space, with individuals displaying restricted movements at greater depths during the day, and larger movements on the surface at night. Hydrophis curtus generally occupied space in deep water within the bay, while H. elegans were restricted to mud flats in inundated inter-tidal habitats. The overlap in space used between day and night showed that individuals used different core areas; however, the extent of areas used was similar. Conclusions: This study demonstrates that by incorporating the capacity to dive in analyses of space use by sea snakes, changes over a diel cycle can be identified. Three-dimensional use of space by sea snakes can identify spatial or temporal overlaps with anthropogenic threats (e.g. trawling, dredging) and help develop targeted management policies that mitigate any adverse effects to ensure healthy populations of sea snakes.