Mid-summer fish behavior in a high-latitude twilight zone

Stein Kaartvedt, Svenja Christiansen, Josefin Titelman

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The behavior of the mesopelagic fish Benthosema glaciale was studied at 60°N in mid-summer. We hypothesized that diel vertical migration (DVM) is constrained by short and dusk nights (surface illumination > 10−2 μmol m−2 s−1) and that individuals are active at depth during the long summer days. Submerged echosounders provided high-resolution data throughout the water column. During the day, a part of the population ascended toward the increasing daylight. Short vertical relocations were followed by minutes of vertical inactivity. Swimming included horizontal turns and loops associated with the vertical steps. Normal DVM was initiated ~ 4 h before sunset and reflected independent individual decisions. The fish initially ascended stepwise but switched to mostly straight upwards swimming attaining 3–4 cm s−1. Their vertical speed was faster than the slow ascent of isolumes and even the deepest living fish potentially could reach upper layers shortly after sunset. However, many individuals aborted their ascent and returned to depth before the darkest time of the night, while others returned downward closer to sunrise. The daytime swimming and individual variability in diel migration behavior have implications for encounters with prey and predators in the twilight zone and the biological carbon pump. A principal conclusion is that mesopelagic fishes can modify their behavior and migration patterns to suit a wide range of changing conditions.
Original languageEnglish (US)
JournalLimnology and Oceanography
StatePublished - May 19 2023
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2023-05-22
Acknowledgements: The fieldwork was funded by the King Abdullah University of Science and Technology (KAUST), Saudi Arabia. The authors thank Anders Røstad and Thor A. Klevjer (deceased) for invaluable logistic help and the Institute of Marine Research (IMR), Norway, for providing land-based facilities for collection of the acoustic data. The authors thank Dag L. Aksnes for access to light data. The authors acknowledge the thorough and constructive advice by two anonymous reviewers who helped making this a better contribution. Stein Kaartvedt and Svenja Christiansen 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. S.K. also received funding from the Research Council of Norway, projects 294819 and 301077.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science


Dive into the research topics of 'Mid-summer fish behavior in a high-latitude twilight zone'. Together they form a unique fingerprint.

Cite this