Individual daytime swimming of mesopelagic fishes in the world's warmest twilight zone

Beatriz Sobradillo, Svenja Christiansen, Anders Røstad, Stein Kaartvedt

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We assessed the activity and swimming patterns of mesopelagic fishes in the Red Sea using bottom-moored, upward-facing echosounders deployed at 555 and 700 m depth. The vertically migrating mesopelagic scattering layer descended close to the bottom during daytime. This permitted assessment of behavior at mesopelagic depths by applying acoustic target tracking for individuals traversing the acoustic beam. Swimming activity did not fit the notion of torpid behavior in the daytime habitat. The fishes were moving continuously, with a prevailing downward direction before noon and upward after, though individuals were swimming in both directions at all times. They moreover were swimming horizontally at estimated speeds of ∼2.1 cm s−1, suggesting ∼0.5–1 body length s−1, intermittently turning. High activity at high temperatures suggests high respiration at depth, considered a key element for the active carbon pump.
Original languageEnglish (US)
Pages (from-to)103897
JournalDeep-Sea Research Part I: Oceanographic Research Papers
StatePublished - Oct 20 2022

Bibliographical note

KAUST Repository Item: Exported on 2022-11-07
Acknowledgements: The fieldwork was funded by the King Abdullah University of Science and Technology (KAUST), Saudi Arabia. Beatriz Sobradillo, Svenja Christiansen and Stein Kaartvedt were funded by the SUMMER project within the EU Horizon 2020 research and innovation programme (grant agreement number 817806; Sustainable Use of Mesopelagic Resources) during the preparation of the manuscript. We would like to thank the crew of RV Thuwal for their assistance during the fieldwork. We are grateful for the comments and suggestions by two anonymous reviewers.

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science


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