Untitled - CNR

Fishery and Sea ResourcesFigure 2: Arnoglossus laterna (scaldfish). (a) Selectivity curves for individual hauls(thin lines) and mean curve (thick line) according to [5]. (b) Confidence regions (95%)for expected mean REML values of Selection Range (pred.SR) plotted against the 50%retention length (pred.L50) calculated by the best model, based on the lowest value ofAkaike’s Information criterion (AIC). DM38: diamond-mesh codend; SM-38: squaremeshcodend.which was adjusted as a two-level factor(DM38=0; SM38=1). The choice of themodel best fitting the data was based onthe lowest value for Akaike’s InformationCriterion-AIC [10].The haul-by-haul maximum likelihood ofselectivity parameters for individual haulswas estimated using the CC2000 software[11]. Models, including between-haulvariation, were estimated using the EC-Modeller software (Constat, 1995), whichadopts the REML method (REsidual MaximumLikelihood) proposed by [5].Traditionally the results of a selectivityanalysis is a logistic curve were the inflexionpoint coincide with the L50 or 50% retentionlength.3 ResultsOverall, 21 valid hauls were performedin the first cruise and 27 in the second.The collected data allowed analysisof the selection characteristics for 9species: scaldfish (Arnoglossus laterna),broad-tail shortfin squid (I. coindettii), Europeanhake (M. merluccius), red mullet(M. barbatus), Norway lobster (N. norvegicus),common pandora (Pagellus erythrinus),deepwater rose shrimp (Parapenaeuslongirostris), Mediterranean horse mackerel(Trachurus mediterraneus) and poorcod(Trisopterus minutus capelanus). TheREML parameter estimates of each codendobtained from direct analysis (no fixed effects)are shown in Table 1. Individualhaul and mean curves are shown in Figure2a to Figure 10a. The estimated alphaparameters of all species are listed inTable 2, along with their standard devia-1862