Flexible behaviour in a mesopelagic fish (Maurolicus muelleri)

Svenja Christiansen, Thor A Klevjer, Anders Røstad, Dag L Aksnes, Stein Kaartvedt

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Abstract Variability of mesopelagic scattering layers is often attributed to environmental conditions or multi-species layer composition. Yet, little is known about variation in behaviour among the individuals forming scattering layers. Based on a 10 months high-resolution dataset from stationary echosounders in a Norwegian fjord, we here assess short-term and long-term behaviour of a single mesopelagic fish species, the pearlside Maurolicus muelleri. The daytime vertical extension of the monospecific pearlside scattering layers spanned four orders of magnitude ambient light in the autumn and winter and less than one order of magnitude in summer. While the main layers tracked relatively stable light levels over daytime, some individuals actively crossed light gradients of up to 1.5 orders of magnitude. This included individuals that moved between scattering layers, and apparently bold individuals that made regular upward excursions beyond the main population distribution. During the daytime, M. muelleri mitigated the risk of predation by forming tight groups in the upper scattering layer and, at light levels >10−6 µmol m−2 s−1, by instantly diving into deeper waters upon encounters with predators. Our observations suggest that individual, and probably state-dependent, decisions may extend the pearlsides’ vertical distribution, with implications for predator–prey interactions.
Original languageEnglish (US)
JournalICES Journal of Marine Science
StatePublished - Apr 14 2021

Bibliographical note

KAUST Repository Item: Exported on 2021-04-21
Acknowledgements: The field work was funded by King Abdullah University of Science and Technology (KAUST). D.L.A. and S.K. were supported by the EU-project SUMMER (Grant agreement number: 817806) during preparation of the manuscript. We would like to thank Rita Amundsen, Ingrid Solberg, Eivind Dypvik, Perdana Karim Prihartato, and the crew of RV Trygve Braarud for their assistance during the field work. We would like to thank two anonymous reviewers for their very helpful suggestions and Josefin Titelman for providing valuable comments during manuscript revision.

ASJC Scopus subject areas

  • Ecology
  • Ecology, Evolution, Behavior and Systematics
  • Oceanography
  • Aquatic Science


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