Between December 1993 and September 1999, 752 mature female plaice were tagged with electronic data storage tags (DST; see preceding abstract) and released at eight North Sea locations. Tidal data recorded by returned DSTs were used to reconstruct the movements of 145 free-ranging plaice for periods of up to 512 days, with a total behavioral record of 20,403 days of data.

The results revealed a seasonal subdivision of the population sampled into three geographically distinct sub-units. Between May and October, these sub-units were centred on Amrum Ground to the east, Ekofisk Field to the north, and between the north coast of East Anglia and Dogger Bank to the west. During the spawning period (December-April), individuals from both the eastern and northern sub-units were found simultaneously on the German Bight spawning grounds, while individuals from all three sub-units visited spawning grounds in the Southern Bight.

The only fish in the current study to leave the North Sea were a sub-set of the western sub-unit that visited spawning grounds in the eastern English Channel. The western and eastern sub-groups recorded a seasonal rise and fall in ambient temperature, whereas the northern sub-group spent the summer in deep, cold, thermally-stratified water.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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