Estimated impact of the horizontal net opening in the calculation of abundance indices in the trawl survey = Incidenza della stima dell'apertura orizzontale della rete nel calcolo degli indici di abbondanza nei trawl survey medits

The effects of horizontal net opening in the calculation of abundance indices of Mullus barbatus (Linnaeus, 1758) (Osteichthyes: Mullidae) and Aristaeomorpha foliacea (Risso, 1827) (Crustacea: Decapoda) were investigated in the FAO Geographical Sub-Area 11. New measurements on the performance of the bottom trawl gear were collected in 2011-2012 in order to construct a predictive model of the horizontal net opening. The abundance indices were estimated and compared with an old predicted model. A high correspondence between the two sources of data has been found for M. barbatus, while for A. foliacea a difference in the absolute values for different years has been highlighted.