Untitled - CNR

Marine research at CNRTable 2: Alpha parameter estimates, standard deviation (SD), t-value, degrees of freedom(dof) and p-value for the species studied. α is the vector that determines the direction andmagnitude of the influence of the explanatory variables on selectivity parameters (L50and SR).the logistic selectivity curve:r(l) =ev1+v2l, (1)1 + ev1+v2l where r(l) is the probability that a fish oflength l is retained, given that it entered thecodend [9], and ˆv = (v 1 , v 2 ) T is the vectorof the selectivity parameters. The modelof between-haul variation proposed by [5]was then used to investigate the betweenhaulvariation of the selectivity parametersv 1 and v 2 by twine thickness, allowing amean curve to be estimated for each codendmesh.Finally the selectivity data were modelledaccording to [5] by estimating the individualcontribution of some explanatory variablesto the selectivity parameters. All possiblelinear combinations of the selectivityparameters as functions of the explanatoryvariables mesh configuration (mi), fishingdepth (di) and codend catch size (ci) weretested. All were adjusted as continuousvariables except for mesh configuration,1861