Publication Abstract

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

J. van der Kooij, D. Righton, E. Strand, K. Michalsen, V. Thorsteinsson, H. Svedäng, F. Neat and S. Neuenfeldt

The behavioural response of cod 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 prior to tagging, or by pressure reduction during a rapid ascent from the seabed). The equilibration enabled the cod to regain demersal residence. The rate of descent averaged 10 m d^-1 (ranging from 2 m d^-1 to 23 m d^-1) over periods of less than a day to one month. Descent rates were inversely proportional to seabed depth i.e. were more rapid in shallow water and, for cod in the southern North Sea, were related to water temperature, findings consistent with historic results achieved in the laboratory. Modelling of swimbladder volume during equilibration suggested that cod were negatively buoyant most of the time. The results imply that swimbladder functionality is retained after 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 the interpretation of cod behaviour and its impact upon biomass estimates obtained from acoustic and trawl surveys.

Reference

J. van der Kooij, D. Righton, E. Strand, K. Michalsen, V. Thorsteinsson, H. Svedäng, F. Neat and S. Neuenfeldt (2007) Life under pressure: insights into cod swimbladder function from electronic data storage tags. ICES Journal of Marine Science, 64: 1293-1301