Untitled - CNR

Fishery and Sea ResourcesFigure 3: Observed (Rv) and expected (all BHs) values of the anchovy recruit numbers(thousands) over years. Expected values were obtained by fitting the Beverton-Holtmodel to log values of recruit numbers estimated by split year VPA. The Beverton-Holtwas simple or ad hoc modified with predictor variable F and Fond, i.e. annual and autumn(ond = October-November-December) Po River flow rate (m 3 · s −1 ) in previouscalendar year, respectively. Redrawn from [16].related to trophic rather than temperaturechanges.4 Future perspectivesIn order to obtain the most reliable estimatesof stock abundance, the use of differentmethods to estimate some input dataas well as different population dynamicsmethods will be evaluated. In the formercase, an example is given by the use ofthe natural mortality rates M taken as variable(instead of constant) over age class;this feature was taken into account in themost recent assessments of the two Adriaticstocks of anchovy and sardine (GFCM-SCSA, Malaga, 30 November - 4 December2009 http://www.gfcm.org/gfcm),where the values of M for the age class 0(i.e. recruits) were estimated to be quitehigher than in previous assessments. Aboutthe use of different models, the analysisperformed with VPA could be repeated usingthe Integrated Catch Analysis or ICA.This treats the catch at age and auxiliary informationon fish abundance at sea (e.g. derivedfrom echo-surveys) as measured witherror in contrast with classic VPA [14].Therefore, the numbers of both recruits andspawners estimated using variable M at ageand ICA could be related again to the mentionedenvironmental parameters, on thebasis of updated time series. In conclusion,further investigations in both stock assessmentand biology (e.g. growth patterns)could provide a better understanding of theinfluence of environment on the recruit-1902