Untitled - CNR

Fishery and Sea Resourcesthen, after a strong decrease it showed aslight recovery in the period 1983-85 justbefore the collapse of 1986-90. The recoverystarted in 1994 and after a new fall(2004-2005) the stock reached a high peakin 2008 and in 2009 it maintains a goodlevel well above the mean of all the studiedperiod. Anchovy is the species with thehighest biomass level in the western sideof the Adriatic Sea in these last years.Sardine stock starting from a very low levelof biomass (1976-80) reached the maximumvalue in 1983; then after a periodof normality (1986-95), sardine populationdiminished and remained stable at very lowlevels with minor fluctuations. In these lastyears sardine population shows evidenceof a slight recovery.Sprat stock shows more drastic fluctuationsthan the other species even if the referencescale is much smaller. These last years arecharacterized by low levels of abundanceapart for the peak of 2006 that was similarto the previous peaks of 1987 and 1992.The distribution pattern of the total pelagicbiomass in 2006 is shown in Figure 3.The high density areas represent 14.6%of the covered area and contain 36.5% ofthe total biomass. The medium densityareas represent 47.7% of the investigatedarea and contain 50.9% of the total pelagicbiomass. Finally the low density areas represent37.7% of the investigated area andcontain only 12.5% of the total biomass.The low density region is of no interest tofishermen. The maps of spatial distributionof the target species were represented inFigure 4. The intervals used for these mapswere chosen with the same principle of theones of total pelagic biomass.3.2 Preliminary results on thespatial distribution of anchovyand sardine juvenilesderived from past surveys(2004-2008)Figure 5 and 6 show the distribution of anchoviesand sardines juveniles in westernAdriatic Sea during the historical surveysfrom 2004 to 2008. In red is marked thepresence of anchovy juveniles along theacoustic cruise route and in blue the sardinejuveniles presence.Anchovy juveniles presence, in the studyarea, resulted mainly concentrated fromPo delta southwards until Brindisi even ifthere’s no continuity of distribution overthe years. Anchovy juveniles were almostalways concentrated near the coast (depth< 50 m).Sardine juveniles are more sporadic anddistributed mainly near Gargano Promontoryand Manfredonia Gulf.3.3 Preliminary results of thestudy on the acoustic propertiesof anchovy postlarvaeFrom a preliminary analysis based onsome monospecific hauls for anchovy postlarvae(individuals < 4 cm), the impressionis that the acoustic behaviour of thesepost-larvae is similar to that of adults ofthe same species, with a significant role ofthe swim bladder in sound reflection. Theresults are reported in Figure 7. The 38kHz echogram shows the aggregations ofanchovy post-larvae in correspondence ofa monospecific haul.The histograms show the comparison ateach working frequency of biologic data(measured sizes) converted into Target2024