| Summary: | Vertical movements of fish stocks can be studied by means of acoustic data from surveys, and diurnal related cycles in behaviour is often reported. To what extent the movements observed by this method reflect behaviour of individual fish, or alternatively, reflect probabilities of fish to be distributed at bottom or in the pelagic zone at specific time periods is unknown. Improved knowledge of fish natural behaviour is essential to understand variation in availability and efficiency of survey trawls as well as the actual target strength used in acoustical surveys. Data storage tags (DST) represent a new tool to observe individual fish behaviour in relation to environmental factors like temperature, depth and light. In this paper the results from tags attached to North-East Arctic cod, released at spawning ground and during feeding, are presented and analysed with emphasise on implication of fish behaviour on efficiency of abundance surveys.
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