Scientia Marina, Vol 66, No S2 (2002)

Distribution of the Mediterranean hake populations (Merluccius merluccius smiridus Rafinesque, 1810) (Ostheichthyes: Gadiformes) based on six years monitoring by trawl-surveys: some implications for management


https://doi.org/10.3989/scimar.2002.66s221

Lidia Orsi Relini
Dipartimento per lo studio del Territorio e delle sue Risorse (Dip.Te. Ris), Università di Genova Laboratorio di Biología marina ed Ecologia animale, Italy

Costas Papaconstantinou
National Centre for Marine Research (NCMR), Institute of Marine Biological Resources, Greece

Stjepan Jukic-Peladic
Institut Za Oceanografiju i Ribarstvo, Croatia

Arnauld Souplet
IFREMER, Station de Sète, Direction des Ressources Vivantes, Lab. Dinamique des Systemes Productifs, France

Luis Gil de Sola
Instituto Español de Oceanografía, Centro Oceanografico de Malaga, Spain

Corrado Piccinetti
Laboratorio Biologia Marina e Pesca, Università di Bologna, Italy

Stefanos Kavadas
National Centre for Marine Research (NCMR), Institute of Marine Biological Resources, Aghios Kosmas, Greece

Marco Rossi
Dipartimento per lo studio del Territorio e delle sue Risorse (Dip.Te. Ris), Università di Genova Laboratorio di Biología marina ed Ecologia animale, Italy

Abstract


On the basis of trawl survey data collected during the MEDITS project (1994-1999), the distribution of Mediterranean hake populations was described in coastal areas corresponding to about three quarters of both the latitudinal and longitudinal extensions of the Mediterranean Sea, and in the 0-800 m range. Abundance and biomass indices (in terms of number and kg per km2) are presented in 15 geographical sectors and 40 subareas from the Alborán Sea to the Aegean Sea. A statistical analysis by generalized linear modelling performed on such indices per main national blocks (Greece, France, Italy and Spain), and considering the effects of the six years of sampling and the depth, showed that biomass increased from west to east, while for all areas the most significant depth effect appeared between 100 and 200 m, corresponding to the depth range that hosts most of the summer nursery areas. The overall size-frequency distributions in shelf and slope waters, average sizes and total mortality coefficient Z per sector showed that the bulk of the MEDITS samples consisted of young individuals and, with only a few exceptions (western Sardinia, central Aegean), a generalized condition of growth overfishing was apparent. However, no negative trend was found, either in biomass or in average size of fishes, during the six years of the present study. Recruitment patterns were studied by distinguishing the youngest fish as Gaussian groups (modal length from 6 to 9 cm total length) in length-frequency distributions of each subarea and main stratum (shelf and slope). Considering the timing of MEDITS surveys (May-July), this approach emphasised the nurseries in the northern part of the western Mediterranean (Gulf of Lions, Ligurian Sea, northern Tyrrhenian Sea) and in the northern central Mediterranean, where recruitment occurs mainly during spring. On the other hand, few recruits were found in part of the central and particularly in the eastern Mediterranean, where recruitment occurs mainly in summer. MEDITS recruitment patterns therefore gave support to distinctions among Mediterranean hake populations, previously suggested on the basis of vertebral counts and other morpho-physiological, albeit fragmentary, data. In particular the central Mediterranean hake populations do not seem to be homogeneous, with an Adriatic unit very close to the northwestern one. The MEDITS experience therefore suggests that future management measures could take into account both general and regional patterns, the latter concerning mainly the younger fraction of the populations.

Keywords


hake; Merluccius merluccius; Mediterranean subspecies; biomass; abundance; size structures; spring recruitment patterns; stock identification

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Copyright (c) 2002 Consejo Superior de Investigaciones Científicas (CSIC)

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