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AbstractNocturnal migration of mesopelagic fish into surface waters is well-documented. Yet, although there is increasing evidence of individual-based deviations from average population migrations and of the importance of small-scale individual behavior for predator-prey interactions and energetic cycling, little is known about what mesopelagic animals do when in upper waters. Using high-resolution data from an upward-facing, moored, split-beam echosounder we analyzed the night-time individual vertical swimming behavior of pearlsides (Maurolicus muelleri) over one winter. The population behavior is characterized by migration to the surface after sunset, “midnight-sinking” and another migration to the surface in the morning, followed by return to the daytime habitat. Focusing on individuals unveiled diverse behavioral patterns during different phases of the migration. After ascending to upper layers at dusk, M. muelleri leaves the surface waters, not by sinking, but by actively swimming in a step-wise pattern characterized by relocations alternated by pauses. Following the descent, vertical swimming is sustained at lower levels. Around midnight, the vertical swimming direction changes from predominantly downward to upward. Several hours before dawn, the fish start ascending toward the surface in a step-wise pattern. During population ascent in the afternoon and descent in the morning, some individuals at the fringes of schools migrate without intermittent pauses. This study documents the feasibility of using submerged, stationary echosounders in unveiling the individual behavior of mesopelagic fish.
CitationChristiansen, S., Titelman, J., & Kaartvedt, S. (2019). Nighttime Swimming Behavior of a Mesopelagic Fish. Frontiers in Marine Science, 6. doi:10.3389/fmars.2019.00787
SponsorsWe thank Anders Røstad and Thor A. Klevjer for invaluable logistic help with the acoustic studies. We would like to thank Helge Balk for assistance with the Sonar5-Pro software. Comments from the two reviewers helped to improve the manuscript. Funding. The fieldwork was funded by the King Abdullah University of Science and Technology, Saudi Arabia.
PublisherFrontiers Media SA
JournalFrontiers in Marine Science
CollectionsPublications Acknowledging KAUST Support
Except where otherwise noted, this item's license is described as Archived with thanks to Frontiers in Marine Science