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Marine research at CNRFigure 7: Pagellus erythrinus (common pandora). For the explanations see caption Figure2.remain unchanged, however the conclusionsmust be considered no more than anindication as any variance estimates willsurely be underestimated [5]. Worthy ofmention is that in some of those studies(see Table 3), selectivity was measured usingthe covered codend technique where acover was not supported by circular hoopsas suggested by Main and Sangster (1991)and likely this does not prevented maskingeffects. Furthermore, the parameterestimates for European hake (M. merluccius)obtained by [12], are extreme resultsand may be caused both by the large meshsize used in the control codend and by discrepanciesbetween the applied paired-gearmethod and the other covered codend experiments(see Table 3). In fact, [19], [20]and [21] pointed out that the reliability ofselection parameters based on data fromsea trials depends both on the structure ofthe data collected and on the methods ofmeasuring gear selectivity. Recent studiesconfirmed that the methods referred toas paired-gear methods [9] may lead to biasedresults and overrepresentation of extremeparameter estimates (Frandsen et al.,2006a, 2006b), [21]. We noted that manyexperiments did not provided the gear designand it was difficult for us to explainthe variability observed in the reviewed selectivityresults. Usually selectivity dataare normally presented for a specific gear.Different gears of the same type may varyin size, design and construction, materialused, rigging and operation, and all mayhave an effect on selection [22, 23, 24].However, where the information was availablewe take note of missing measurementof the mesh openings [17, 13, 18]and the results were based upon nominalmesh sizes. In some others the authorsdid not assessed the selectivity of the codendsensu-strictu, but they measured thecombined selectivity of the extension andthe codend as the cover enclosed both thetwo (i.e. [15]). In the current studies,using the information from the seasonaltrawl surveys carried out along the Italiancoasts we decided a suitable location of areasand period to assess the selectivity ofthe main commercial species according to1867