Συγκριτική μελέτη της επίδρασης περιβαλλοντικών παραγόντων στην κατανομή των ιχθύων Prionace glauca ( γλαυκός καρχαρίας) και Xiphias gladuis ( ξιφίας), του πελαγικού οικοσυστήματος της Ανατολικής Μεσογείου

TL;DRAbstract

Swordfish (Xiphias gladius) and blue shark (Prionace glauca) are two apex predators in the pelagic ecosystem of the eastern Mediterranean Sea. Our current knowledge on their spatio-temporal distribution patterns and the effect that the surrounding environment has on them is limited. During the period of 1998-2001 and 2003-2005, data gathered from a series of surveys on the Greek surface drifting longline fleet were analyzed in order to estimate the effect of spatial, temporal, environmental and operational factors on the abovementioned species distribution and relative abundance (expressed in number of fish caught per 1000 hooks deployed). Application of generalized additive models allowed the identification of various parameters influencing catches as well as the contribution of each one. The optimum model was derived using a cross validation procedure which was based on the principal of parsimony: this principal tends to select those variables that depict more closely the actual tren

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