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Observations of cod behaviour reveal insights into the function and properties of the swimbladder under pressure

Kooij, Jeroen van der; Righton, David; Michalsen, Kathrine; Thorsteinsson, Vilhjalmur; Svedäng, Henrik; Neat, Francis
Working paper
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URI
http://hdl.handle.net/11250/100893
Date
2006
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  • ICES CM documents authored by IMR scientists (1949-2011) [3138]
Abstract
Atlantic cod (Gadus morhua L.) is a highly adaptive boreal species with a

broad distribution through different ecosystems in the North Atlantic. Diet,

environmental factors and population dynamics vary enormously throughout

this range, and behaviours are therefore extremely plastic. However, the

behaviour of cod will always be constrained by physiology, be it temperature

tolerance, swimming speeds or buoyancy control. Cod, like other gadoids,

are physoclists, i.e. they have a closed compliant swimbladder that can be

filled or emptied in order to achieve neutral buoyancy at any depth. Pressure

changes caused by vertical movements lead to expansion and compression

of the swimbladder as individuals ascend or descend respectively. Over time,

changes in the volume of the swimbladder will occur so that individuals can

maintain neutral buoyancy with the minimum effort. Here, we have used data

collected by cod tagged with electronic tags and released in five different

regions of the NE Atlantic to investigate the neutrally buoyant descent rates of

cod that are moving from shallow residence depths to deeper ones. First, we

describe the patterns of vertical movement and rates of descent in the

recuperation period following tagging, when the swimbladder is re-inflating to

achieve neutral buoyancy at capture depth. Using this recuperation behaviour

as an indication of swimbladder inflation during extreme depth changes, we

then describe similar patterns of natural behaviour during medium-term

transitions from shallow to deeper depths as cod migrate between different

areas. Third, we assess the significance of behaviour of this kind, its

relationship to environmental variables and how it varies between regions and

seasons.
Publisher
ICES
Series
ICES CM documents
2006/Q:13

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