Berumen, Michael L.
Cochran, Jesse E.M.
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
Red Sea Research Center (RSRC)
Marine Science Program
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AbstractAn aggregation of sexually immature whale sharks occurs at a coastal submerged reef near the Saudi Arabian Red Sea coast each spring. We tested the hypothesis that these megaplanktivores become attracted to a prey biomass peak coinciding with their aggregation. Acoustic backscatter of the water column at 120 kHz and 333 kHz –a proxy for potential prey biomass –was continuously measured spanning the period prior to, during, and subsequent to the seasonal whale shark aggregations. No peak in acoustic backscatter was observed at the time of the aggregation. However, we observed a decrease in acoustic backscatter in the last days of deployment, which coincided the trailing end of whale shark season. Organisms forming the main scattering layer performed inverse diel vertical migration, with backscatter peaking at mid-depths during the day and in the deeper half of the water column at night. Target strength analyses suggested the backscatter was likely composed of fish larvae. Subsurface foraging behavior of the whale sharks within this aggregation has not been described, yet this study does not support the hypothesis that seasonal peaks in local whale shark abundance correspond to similar peaks in prey availability.
CitationHozumi A, Kaartvedt S, Røstad A, Berumen ML, Cochran JEM, et al. (2018) Acoustic backscatter at a Red Sea whale shark aggregation site. Regional Studies in Marine Science 20: 23–33. Available: http://dx.doi.org/10.1016/j.rsma.2018.03.008.
SponsorsWe thank the RV Thuwal captain and crew, Francis Mallon, Lloyd Smith, Ioannis Georgakakis, Brian Hession, Ingrid Solberg, and Joseph DiBattista for field and logistical support. The KAUST Coastal and Marine Resources Core Lab (CMRCL) and Dreams Divers (Jeddah, Saudi Arabia) facilitated many additional aspects of fieldwork. We thank Riata Amundsen for her substantial help in zooplankton identification, and Darren Coker for analysis help. This study was funded by King Abdullah University of Science and Technology (KAUST).