ALLOZYMIC AND MORPHOMETRIC EVIDENCE FOR 2 STOCKS OF THE EUROPEAN ANCHOVY ENGRAULIS-ENCRASICOLUS IN ADRIATIC WATERS

Allozyme electrophoresis and morphometric analyses were used to invest igate the stock structure of European anchovies (Engraulis encrasicolu s L.) captured by Italian vessels in the Adriatic Sea. Twenty four put ative enzyme loci were studied, al of which exhibited genotypic propor tions in accordance with Hardy-Weinberg predictions. Two loci, IDHP-2 (isocitrate dehydrogenase, 1.1.1.42) and G3PDH-2 (glycerol-3-phospha te dehydrogenase, 1.1.1.8), showed significant allele-frequency differ ences among samples. IDHP-2100 frequencies ranged between 0.35 and 0. 88, with lower frequencies recorded in northern waters and areas close to the Italian coastline, while G3PDH-2100 frequencies followed a si milar, if less distinct, pattern. For both loci, the trends observed w ere spatially stable over a 2 yr sampling period. A putative stock-bou ndary was superimposed onto a map of IDHP-2100 frequencies, and a boo tstrapped dendrogram confirmed the genetic separation of the two putat ive stocks, one located around the north-western Adriatic and the othe r in the central-southern region. Canonical variate analysis (CVA) of morphometric data collected using a ''truss network'' indicated that t he two putative stocks were morphologically distinct; 89.6 and 88.3% o f north-western and central-southern anchovies, respectively, were cor rectly assigned by discriminant-function analysis. This variation may be related to the presence of two anchovy colour phenotypes, silver an d blue, in the Adriatic Sea. Silver anchovies are characteristic of no rthern areas, while the larger blue fish are found mainly in the deepe r southern waters. Current assessment models for the fishery are based on the concept of a consistent identity between consecutive catches a t single ports, which our data reject. We discuss the possibility of p artitioning fishing effort based on the proportions of the two stocks landed at individual ports.