A geostatistical approach to the assessment of the spatial distribution ofParapenaeus longirostris (Lucas, 1846) in the central-southern Tyrrhenian Sea

The spatial distribution of the abundance indices of the deep-water rose sh rimp Parapenaeus longirostris was investigated applying geostatistical tech niques on data collected in the central-southern Tyrrhenian Sea from bottom trawl surveys carried out in the autumn since 1994. Experimental variogram s (auto and cross) were constructed on the variable "abundance index", expr essed in kg/km(2) and those variogram models best describing the spatial co ntinuity were detected and validated by the jackknife technique. The spatia l structure of the "abundance index", exhibiting a similar pattern througho ut the surveys, was described by a spherical model and characterized by a s patial continuity at a small scale level in the whole area. The linear geos tatistical approach was applied by different kriging techniques and the est imates extended to the spatio-temporal dimension, in this case adopting the co-regionalized models and applying the cokriging technique. This method a pplied to the spatial dimension (abundance index and depth). Also, linking the spatial and temporal dimension of the abundance indices, measured in tw o different years, contributed to represent a more accurate picture of the abundance distribution, and allowed the detection of a temporal persistence of the localization of areas with higher abundance, reducing the standard deviation of the estimation error. This information, if coupled with an ana lysis of the geographical allocation of the fishing effort, could be of imp ortance in stock assessment, allowing some variant application of the compo site surplus production models.