Untitled - CNR

Marine research at CNRFigure 2: Anchovy recruit numbers (thousands) estimated by VPA in split year x+1 areplotted as a function of Po River flow rate (m 3 · s −1 ) of the calendar year x from 1976 to2000. The results of simple linear regression analysis are shown.tent with some features of the distributionof both anchovy and sardine in the Adriaticsystem. Sardine spawning grounds are inthe eastern part of the Adriatic Sea, correspondingto the northern area off the DugiOtok Island and the southern area aroundthe exterior of the mid-Dalmatian Islandsand extending offshore to Palagruza, thusmiles away from the Po River. On theother hand, the main spawning areas of anchovyare in the coastal waters of the westernAdriatic, with the largest numbers ofeggs being observed in the Gulf of Triesteand off the Po River delta [8, 24, 11,10, 5]. Moreover, in the Adriatic Sea, anchovyspawn at lower values of salinitythan sardine and relatively low salinity valuesare observed just off Po River delta[23, 25]. For all these reasons, the statisticallysignificant influence of Po Riverflow rate obtained for anchovy recruitmentrather than sardine one was expected and,thus, it is a consistent pattern. Finally,insight about the role of Po River runoffwas also gained from the mentioned investigationson the growth pattern of youngstages of both species. The instantaneousgrowth rate estimated for sardine late larvae(0.20 mm day-1) resulted to be lowerthan those estimated for anchovy (0.46 and0.64 mm·day −1 in June and November, respectively).In particular, in the case ofanchovy, length at age data of individualscaught in November were significantly(p < 0.001) higher than those collected inJune. These results are not in agreementwith the general pattern observed in anotherAdriatic ground (Ortona), where theinstantaneous growth rate showed a highervalue in May (0.82 mm·day −1 ) and decreasingin August (0.54 mm·day −1 ) andNovember (0.55 mm·day −1 ) [26]. Spatialand seasonal changes in environmentalconditions largely affected the instantaneousgrowth rate of anchovy. Positive effectsof temperature and food on the growthof fish are well documented [14, 20, 16]and the higher growth rate in November offthe Po River delta, when the flow rate displaysa seasonal peak [21, 16], could be1901