RESEARCH ARTICLE Oceanographic habitat, growth and mortality of larval anchovy (Engraulis encrasicolus) in the northern Aegean Sea (eastern Mediterranean) Stylianos Somarakis Æ Nikolaos Nikolioudakis Received: 28 February 2007 / Accepted: 22 June 2007 / Published online: 17 July 2007 Ó Springer-Verlag 2007 Abstract Data from two ichthyoplankton surveys carried out during June 1995 and June 1996 were used to study the broad scale distribution patterns of anchovy eggs and lar- vae over the northern Aegean Sea continental shelf and the regional/inter-annual variability in growth and mortality rates of larvae. Two major spawning grounds were iden- tified. One in the east, located in the area influenced by the Samothraki gyre (SG), in which a large amount of en- riched, modified Black Sea water (BSW) is entrapped and one in the west, associated with zooplankton-rich waters in the semi-enclosed Thermaikos gulf close to several river mouths. In the NE Aegean, anticyclonic gyres generated over the continental shelf and fed by the circulating stream of BSW (like the SG) may act as retention areas for larval anchovy. In the west, the high enclosure of the Thermaikos Gulf contributes to reducing offshore dispersal. Major changes were observed in egg and larval abundance as well as larval mortality between June 1995 and June 1996 in both the western and eastern part of the continental shelf. Mean abundance of eggs and early larvae was >5 times higher in 1996 than in 1995, when waters were signifi- cantly cooler, fresher and richer in mesozooplankton. Larval survival decreased from 79 to 69% day –1 in the east and from 89 to 74% day –1 in the west between 1995 and 1996. Hence increased egg production was coupled with higher larval mortality during June 1996. Furthermore, a highly significant positive relationship between larval mort- ality (Z) and mean egg abundance (A) emerged (Z = –0154 + 0.205 log[A], r 2 = 0.96, n = 7) when data from this study and a similar study in the NW Mediterranean were re- gressed. Mean growth rate of anchovy larvae in the study area (~0.5 mm day –1 ) did not differ significantly between areas/years. A marked ontogenetic change was observed in the otolith size/recent otolith growth-on-fish size relation- ships, which exhibited significant inflection points at ~6 mm formalin preserved length. This change seems to coincide with performance (e.g., catchability) and behav- ioral changes (e.g., onset of vertical migrations) in Euro- pean anchovy associated with the development of the caudal fin (the flexion stage). Introduction The European anchovy is the most important pelagic fish resource in the Mediterranean Sea (Lleonart and Maynou 2002). Three major stocks support the largest anchovy fisheries in the basin. These stocks are genetically dis- tinct, with reduced gene exchanges (Magoulas et al. 1996) and inhabit the NW Mediterranean (Catalan Sea and Gulf of Lions), the Adriatic Sea, and the northern Aegean Sea (Somarakis et al. 2004), i.e., areas with wide continental shelves, high productivity, in relation to the highly oligotrophic character of other Mediterranean basins, and conditions potentially favorable for larval survival (in terms of the ‘ocean triad’ hypothesis, Agos- tini and Bakun 2002). While several aspects of the early life history and recruitment of the NW Mediterranean, the Adriatic, and other smaller Mediterranean anchovy stocks have been studied in detail (NW Mediterranean: Palomera et al. 1988; Palomera and Lleonart 1989; Palomera 1991, 1992; Garcia and Palomera 1996; Garcia Communicated by O. Kinne. S. Somarakis (&)  N. Nikolioudakis Department of Biology, University of Crete, P.O. Box 2208, 71409 Voutes Heraklion, Crete, Greece e-mail: somarak@biology.uoc.gr 123 Mar Biol (2007) 152:1143–1158 DOI 10.1007/s00227-007-0761-6