Untitled - CNR

Marine research at CNRExploitation 2006 2007 2008pressure Factor Y/R Factor Y/R Factor Y/RF 0.1 0.67 2.81 0.58 2.60 0.67 2.81Fc 1.01 3.04 1.01 2.83 1.01 3.02F max 1.80 3.14 1.32 2.86 1.58 3.09F double 2.00 3.14 2.00 2.80 2.00 3.07Table 2: Main Biological Reference Points in terms of multiplicative factor of the currentF (Fc) for pink shrimp according to VIT analyses. The absolute Fc were 1.20 (2006), 1.40(2007) and 1.11 (2008).3 Results3.1 Pink shrimpThe surveys show a fluctuating abundancein time with a decreasing phase (2005 to2007) (Figure 3), coherent with the correspondinglandings data decrease. Anexample of fishing mortality rates (F) bysize and fleet segments of female deep waterpink shrimps is shown in Figure 4. Itis clear that trawlers operating in coastalwater catch shrimp smaller than trawlersfishing in distant waters. An example of estimationof Biomass and Yield per recruitby varying current fishing mortality (Fc)by a multiplicative factor of current F is reportedin Figure 5. Assuming no variationin the exploitation pattern, the change infishing mortalities to reach an exploitationcorresponding to F0.1 is reported in Table2. The current fishing mortality, rangingbetween 1.11 (2008) and 1.40 (2007) asabsolute values, produces about 2.8 – 3.1g per recruit. A very similar pattern wasobtained simulating the likely changes inY, B and SSB per recruit in function offishing mortality (F) with the YIELD package.According to the steady state VPA oncommercial data, the stock resulted to beoverfished. Maintaining the current fishingpattern, a reduction of Fc of 33-42% is advisableto reach F0.1. The light loss in Y/Rexpected after moving from Fc to F0.1,ranging between 7 and 8% of the currentvalue, is coherent with knowledge of biologicalparameters (high natural mortalityand quick speed to reach maximum length)of the species (Table 2).Comparing recent Fc (1.34 mean over2006, 2007 and 2008) based on trawl surveysdata (Figure 6) and the F0.1 obtainedin Table 3, a decrease of fishing mortalityof 38% should be adopted to reach a sustainableexploitation in long term.3.2 HakeBiomass indices (sex combined) from trawlsurveys by year show an increasing patternfrom late nineties to 2005-2006, followedby a slight decrease until 2008 (Figure7). The pattern of recruitment and SSBestimated by SURBA on MEDITS trawlsurvey series show a better state of stockabundance in the last years (2005-2007)(Figure 8). Time series of F on femalesderived from GRUND trawl surveys suggestsa quite stable fishing mortality from1994 to 2008 ranging between 0.66 and0.90 (mean 0.75 ±0.07) (Figure 9). Fishing1993