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Conference paper - Peer-reviewed, 2021

Eaten by a cormorant: unexpected return of a tagged Baltic cod

Haase, Stefanie; Hüsy, Karin; Casini, Michele; Radtke, Krzysztof; Krumme, Uwe


Temperature-depth data storage tags (DSTs) continuously store individual measurements of water depth and water temperature of the habitat used by free-ranging fish. To analyse the data, the DSTs need to be returned. Usually they are returned by fishers whereas returns of fish tagged with DSTs that died due to natural causes are rare. During an international tagging project, one DST was returned by an ornithologist which found the data logger in a pellet in a cormorant colony. Although the cod itself was not available since it was already digested, the DST provided 90 days of data prior to the predation event. The cod mostly remained in waters shallower than 40 m and conducted daily in- and offshore movements covering the whole water column, leading to daily temperature differences of up to 8.8 degrees C. In May, during one trip where the cod used very shallow waters (1.5 m water depth) in the morning (09:00 h), it was taken by a cormorant. Digestion, indicated by temperatures of 39.3 degrees C to 41.2 degrees C, took 31 hours. This returned DST emphasizes that large-scale tagging projects should not only raise awareness in the fisheries sector but also among ornithologists when avian predators target the tagged fish species.


data storage tags; Baltic cod; cormorant predation; natural mortality; diel vertical movements

Published in

Book title: Proceedings of 2021 IEEE International Workshop on Metrology for the Sea : IEEE MetroSea 2021
ISBN: 978-1-6654-1458-6, eISBN: 978-1-6654-1458-6
Publisher: Institute of Electrical and Electronics Engineers


“IEEE International Workshop on Metrology for the Sea”, Reggio Calabria (Italy), 4-6 October 2021 (virtual)

    SLU Authors

    Associated SLU-program

    Coastal and sea areas

    UKÄ Subject classification

    Fish and Aquacultural Science

    Publication Identifiers


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