Growth and mortality rates of European anchovy ( Engraulis encrasicolus) in the Adriatic Sea during the transition from larval to juvenile stages

Abstract

Growth and mortality rates of juvenile anchovy ( Engraulis encrasicolus) were estimated from monthly samples collected in the coastal waters off Ortona (central Adriatic Sea). Otolith microstructure analysis was conducted on specimens ranging from 10 to 60 mm TL, including the transition from larval to juvenile stages (i.e. at metamorphosis). Fish were aged by growth increment counts on sagittal otoliths, presuming they were laid down with a daily periodicity. Age estimates ranged from 16 to 96 days, with a good consistency between readings. The hatch date distribution, back-calculated from the date of capture, was spread over a long period (April–February), with three main cohorts hatched in May, August and November. The instantaneous growth rate, calculated for the whole fish sample, was 0.68 mm/day. Nevertheless, the growth rate estimated for each of the main cohorts showed a seasonal trend, being higher in May and decreasing in August and November. The allometric relationship between otolith and fish size changed markedly during the transition from larval to juvenile stages, with a slight decrease of otolith growth rate after metamorphosis. The instantaneous total mortality rates of anchovy, calculated for each of the main cohorts, was lower in May and progressively increased in August and November cohorts, showing an opposite seasonal trend respect to the growth rate.