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A GEOSTATISTICAL APPROACH TO THE ASSESSMENT OF THE SPATIAL DISTRIBUTION OF PARAPENAEUS LONGIROSTRIS (LUCAS, 1846) IN THE CENTRAL-SOUTHERN TYRRHENIAN SEA

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The spatial distribution of the abundance indices of the deep-water rose shrimp Parapenaeus longirostris was investigated applying geostatistical techniques on data collected in the central southern Tyrrhenian Sea from bottom trawl surveys carried out in the autumn since 1994. Experimental variograms (auto and cross) were constructed on the variable "abundance index", expressed in kg/km2, and those variogram models best describing the spatial continuity were detected and validated by the jackknife technique. The spatial structure of the "abundance index", exhibiting a similar pattern throughout the surveys, was described by a spherical model and characterized by a spatial continuity at a small scale level in the whole area. The linear geostatistical approach was applied by different kriging techniques and the estimates extended to the spatio-temporal dimension, in this case adopting the co-regionalized models and applying the cokriging technique. This method applied to the spatial dimension (abundance index and depth). Also, linking the spatial and temporal dimension of the abundance indices, measured in two 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 analysis of the geographical allocation of the fishing effort, could be of importance in stock assessment, allowing some variant application of the composite surplus production models.

La distribution spatiale des indices d'abondance de la crevette rose d'eau profonde Parapenaeus longirostris a ete etudiee en appliquant les techniques de la geostatistique aux donnees collectees dans le centre-sud de la mer Tyrrhenienne au cours des campagnes de chalutage demersal realisees pendant l'automne, depuis 1994. Les variogrammes experimentaux (auto et cross) ont ete construits sur la variable "indice d'abondance", exprimee en kg/km2, et les modeles de variogramme decrivants le mieux la continuite spatiale ont ete determines et valides par la technique du "jackknife". La structure spatiale de l'indice d'abondance a presente le meme aspect pour tous les echantillonages; elle a ete decrite au moyen d'un modele spherique et caracterisee par une continuite spatiale a petite echelle dans toute la zone. La geostatistique lineaire a ete appliquee en utilisant differentes techniques du krigeage, et les estimations ont ete etendues a la dimension spatio-temporelle en appliquant les modeles coregionalises et la technique du cokrigeage. Cette methode, appliquee soit dans la dimension spatiale (indice d'abondance et profondeur), soit dans la dimension spatio-temporelle en considerant l'indice d'abondance echantillonne en deux annees differentes, a contribue a representer une image plus precise de la distribution de l'abondance, et a permis de detecter une persistance temporelle de la localisation des aires a plus grande abondance, en reduisant l'ecart type de l'erreur d'estimation. Cette information, avec l'analyse de l'allocation geografique de l'effort de peche, pourrait etre importante dans l'evaluation des stocks, en permettant l'application, avec quelques variantes, des modeles composites de production.

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/content/journals/10.1163/156854099504040
1999-12-01
2016-08-26

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