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Research article - Peer-reviewed, 2007

Life under pressure: insights from electronic data-storage tags into cod swimbladder function

van der Kooij, Jeroen; Righton, D.; Strand, Espen; Michalsen, Kathrine; Thorsteinsson, Vilhijalmur; Svedäng, Henrik; Neat, Francis C.; Neuenfeldt, Stefan


The behavioural response of cod (Godus morhua) to sudden pressure reductions was investigated in a large electronic-tagging experiment using data collected from 141 cod tagged in five different areas of the Northeast Atlantic. More than 40% of cod exhibited a characteristic equilibration behaviour after a rapid pressure reduction caused either by capture before tagging, or by pressure reduction during a rapid ascent from the seabed, or when migrating to deeper water. The equilibration allowed the cod to regain demersal residence. The rate of descent averaged 10 m d(-1) (ranging from 2 to 23 m d(-1)) over periods of less than a day to 1 month. Descent rates for cod on the Icelandic shelf were inversely related to fish length, i.e. smaller fish descended more rapidly, findings consistent with results achieved in the past under laboratory conditions. Modelling of swimbladder volume during equilibration suggested that cod were negatively buoyant for most of the time. The results imply that swimbladder functionality is retained after the probable barotrauma that would follow a large and rapid ascent, and that rates of gas exchange into the swimbladder may be naturally variable. These findings have implications for assumptions on discard mortality, the interpretation of cod behaviour, and its impact on biomass estimates obtained from acoustic surveys.


behaviour; buoyancy; cod; discard; physoclists

Published in

ICES Journal of Marine Science
2007, volume: 64, number: 7, pages: 1293-1301

Authors' information

van der Kooij, Jeroen
Righton, D.
Centre for Environment, Fisheries and Aquaculture Science Lowestoft
Strand, Espen
University of Bergen
Michalsen, Kathrine
Institute of Marine Research (IMR)
Thorsteinsson, Vilhijalmur
Marine Research Institute
Svedäng, Henrik
Swedish Board of Fisheries
Neat, Francis C.
Marine Laboratory, Fisheries Research Services
Neuenfeldt, Stefan

UKÄ Subject classification

Structural Biology
Behavioral Sciences Biology
Developmental Biology

Publication Identifiers


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