Untitled - CNR

Marine research at CNRFigure 5: Variations of stock Biomass between new (B1) and old (B2) evaluation methods.h, according to species and spawning temperatures[5, 16, 17]. POFs degeneration isa continuous process that has to be categorizedinto an ordinal classification key ofstages, with the additional complexity thatPOF characteristics become less clear withtime and their size is reduced until theymay be confused with late atretic stages[5]. The increasing awareness of the effectthat different water temperatures mighthave on the rates of degeneration of POFs[17] made it necessary to examine the potentialeffect that changes in the averagetemperature of the sea water on differentcruises might have on the degeneration ofPOFs and on the ageing procedures.The very low presence of POF 0, especiallyin 2001, 2005 and 2006 (Table 1), confirmsthe difficult to caught specimen immediatelyafter the spawning, because unfortunately,due to aspect regarding the researchvessel crew watches, the trawl samplingduring night-time is not complete over thewhole night.The old and new histological slides comparison(Table 2; Figure 3) showed an highcorrespondence in the age assignment betweenthe two estimates method. The lastfinding because the POF morphology classificationcriteria do not change respect toliterature (ICES, 2004). The observed differenceswere mainly related to the POFsresorption rate.The large interannual variability ofbiomass is typical for small pelagic fishes,as the European anchovy, however our resultsshowed a greater variation and decreasein stock abundance when the newageing criteria were applied. This findingis also important for fishery managementpurposes, if we take in account the very lowvalues of anchovy biomass in the Strait ofSicily. The evaluations of stock biomassand spawning fraction have to be consideredpreliminary results of an early applicationof DEPM procedures in the study areaand here represent a reference points toevaluate the extent of the variability withinrealistic fluctuations range for the observedtwo parameters. The evaluation of preciseand accurate spawning fraction andbiomass estimates are beyond the scope2121