Vertical movement patterns of juvenile whale sharks Rhincodon typus at a seasonal aggregation in Saudi Arabian Red Sea

Abstract

Background Large marine species have been a focus of scientists and public for their unique role in the ecosystem as well as in conservation. To study the behaviors of large marine species, electrical tagging is a direct and reliable method. Researchers have been utilizing technology advances in biologging tags on multiple spatiotemporal scales. This study provides a detailed insight into the vertical movement of whale sharks in a newly described seasonal aggregation off the coast of Al Lith, Saudi Arabia. Approach In the aggregation season of 2015, two biologging tags were fitted on two juvenile whale sharks and lasted over a period of 22 hours each. Fine-scaled diving behavior was recorded with a sampling rate of 10 Hz and energy consumption was generated from acceleration sensory data. Results Tagged whale sharks exhibited intensive and consistent diving behaviors throughout the day except a prolonged surface swimming in the morning and a brief surfacing around sunset. Deep dives from the two tagged sharks reached 80 meters, which is the depth of this aggregation habitat. In multiple stages of the diel cycle, whale sharks utilized different depths in the water column. Diving speeds also varied among diel stages and between two individuals, most possibly as a strategy of optimizing energy consumption from forage efforts. Combining with previous study on horizontal movement of whale sharks in this aggregation, this study portrays movement behaviors of juvenile whale sharks comprehensively. Conclusions Whale sharks in this aggregation showed a distinct diel vertical movement pattern which also effectively utilizes energy. We hope this study will benefit the management of this hot spot of whale sharks and even larger scale ecosystems, revealing potential excessive human activities (e.g. ecotourism, aquaculture) and global climate issues.