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A model for scaling from individuals to populations using ethotypes

The purpose of this area of work has been to test whether structural features in the otolith can be used to identify and understand behaviours recorded by DST tags. The basic premise is that significant changes in the fish's behaviour are likely to involve changes in the extrinsic and intrinsic factors that influence otolith microstructure. Patterns of behaviour of DST-tagged cod were identified and quantified to determine the frequency and timing of key behavioural phases such as migration, spawning and residence on feeding grounds. In combination with the DST temperature record, the daily increments of recovered otoliths were examined to relate changes in growth conditions with changes in behaviour at scales from days to months. Experiments were conducted with adult cod to parameterise the effects of temperature; size and age for comparison with the long-term natural otolith signal from returned DST tagged cod.

The otolith accretion model developed in the IBACS project (QLRT-2001-01610) has been applied to DST tagged individuals of the Baltic Sea and the North Sea to evaluate output of otolith macrostructure with actual observations of these individuals. However, correlation of otolith microstructure with cod behaviour did not help to identify consistent patterns within ecosystems, although major biological drivers were identified that primarily influence otolith macrostructure between ecosystems. Otolith representative of the cod populations in the different ecosystems are being analysed to identify indicators of habitat characteristics, migration, activity and seasonal growth cycles in order to establish within and among ecosystem variations. Results will have management implications e.g. bearings for identification of stock structure, large scale seasonal migrations as well as trends in environmental impact on population behavioural characteristics.

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United Kingdom
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