Identificazione spazio-temporale delle aree di concentrazione dei giovanili delle principali specie demersali e localizzazione geografi cadi aree di nursery nei mari italiani - NURSERY

Nursery areas of relevant demersal species (Eledone cirrhosa, Merluccius merluccius, Mullus barbatus, Nephrops norvegicus, Parapenaeus longirostris, Phycis blennoides, in all GSAa, Aristaeomorpha foliacea, Illex coindetii, Loligo vulgaris, Pagellus erythrinus, as locally important in some GSAs) were localised in the framework of the NURSERY project. Data collected during trawl surveys (MEDITS and GRUND) carried out in the 7 Italian GSAs from 1994 to 2005 were used. Juveniles were identified analysing the length frequency distribution of trawl survey data and cut-off size (mean of the first modal component+sd) used to split the LFD of each species into juvenile and adult components. Geo-referenced abundance indices were thus used to conduct a geostatistical structural analysis. Localization of the nurseries was obtained by Indicator Kriging, that allows to interpret the localization in terms of probability. This was done after defining cut-off thresholds based on the ranking of the cumulative abundance and the number of hauls, thus following the Effective Juvenile Habitats concept. Maps of the modelled nurseries were then analysed throughout the time to estimate the persistence of the localization. The applied techniques was based on the averaging of the probability contours when these were higher than 0.6. This approach was further complemented with the bayesan gestatistical approach and the spatial indicators approach. Although a certain degree of variability in extension and shape of nursery areas, the results of persistence analysis showed a considerable stability in some locations. Nurseries of species like hake and deep water rose shrimp are overlapping in several areas. Most of nurseries are located inside the territorial waters with the notable exception in the GSAs 16, 17, and 18. The achieved results can be used to support management decisions based on the protection of Essential Juvenile Habitats.