Untitled - CNR

Fishery and Sea ResourcesParameters Pink shrimp Red shrimp HakeL∞ 43 68.9 81.54k 0.68 0.61 0.15t0 -0.2 -0.2 -0.08a 0.0036 0.0013 0.0043b 2.4423 2.636 3.1525L 50% 21.5 37.2 35.6g 0.45 0.54 0.29M 1.04 0.40 0.34F t 2.00 0.80 0.75L' 20.5 n.c. 20Table 1: Parameters used Legenda: L∞, K and t0 = parameters of the special Von BertallanfyGrowth Function (VBGF), asymptotic (or at infinity) length, Brody (or curvature)coefficient, and the theoretical age at zero length; a and b = coefficient of the allometriclength-weight relationship; L50% and g= length at 50% of sexual maturity and the correspondingcurvature (steepness) parameter; M and Fter= natural (scalar) and terminalFishing mortality; L’= length at fully catchability. Lengths are expressed as CarapaceLength (CL; mm) and Total Length (TL; cm) in shrimp and hake, respectively. Weightand time units are gram and year, respectively.spectively, were used to derive the classicalcurve of yield and spawning stock biomassper recruit (Y/R and SSB/R) in function offishing mortality (F) by implementing differentpackages (VIT, [11]; YIELD, [12]).The optimal exploitation was evaluated onthe basis of critical values of F, used as biologicalreference points (BRP).The current fishing mortality (Fc) was assessedwith Virtual Population Analysis(VPA) on length structure of the catches(pseudo-cohort). On the other hand, theMEDITS length frequency distributions(LFD) were used to identify Fc throughthe total mortality (Z). In the case of Pinkshrimp and Hake the estimator of Beverton& Holt and the Length converted catchcurve (LCCC routine in the LFDA package[13]) were used, whereas the SURBA2.20 package [14, 15] was applied for Redshrimp.For the SURBA application, the LFDswere firstly converted in numbers by agegroup using the “age slicing” LFDA routine.Then the numbers at age were usedto estimate time series of fishing mortalityrates, as well as recruitment and SSB(Spawning Stock Biomass) indices. WhenVIT and SURBA were applied with vectorialnatural mortality, the M by size arraywas obtained using the model PRODBIOM[16].Since females of all the investigatedspecies show different length structures(largest size), growth-mortality patterns(more sensitivity to fishery pressure) andhigher contribute to the landings in weight(60-70 % in Pink and Red shrimps) thanmales the present analyses only refer to thefemale fraction of the investigated populations.The main biological parameters usedare reported in Table 1.1992