Do tagging experiments tell the truth? Using electronic tags to evaluate conventional tagging data

For more than a century, scientists have used mark-recapture techniques to describe the spatial dynamics of marine demersal fish species in the North Sea. Although such experiments have provided extensive data sets, the information is limited to the date and position at release and at recapture. Furthermore, these data may be biased due to the distribution of fishing effort. Recently, electronic (archival) data storage tags (DSTs) have successfully been used to reconstruct the movements of free-ranging demersal fish between release and recapture. Data from DST experiments allow the calculation of fisheries-independent migration parameters, and thereby provide a means of evaluating conventional tagging data. We compared the migration patterns of North Sea plaice (Pleuronectes platessa L.) as inferred from a database of twentieth century conventional tagging experiments (CT), with data from 132 plaice tagged with DST. In general, the CT experiments allowed a reliable interpretation of migration patterns, although for certain release areas the migration distances were biased due to the heterogeneous distribution of fishing effort