Distributional response to variations in abundance over spatial and temporal scales for juveniles of European hake (Merluccius merluccius) in the Western Mediterranean Sea

This study deals with the spatial aggregation of juveniles of European hake (Merluccius merluccius) in the Southern Ligurian-Northern Tyrrhenian Seas. Abundance and spatial distribution of 0+ group hake were investigated for a better definition of the geographical boundaries of the nursery areas as well as for the checking on their stability in time and space. The information was also used to test whether distributional area and abundance are correlated. Correlations were described for age 0 individuals. Data are derived from 28 trawl surveys performed between 1985 and 2002. The availability of data from trawl surveys done in different seasons and the relatively long data series made it possible to verify the repeatability of some phenomena such as settlement timing and seasonal spatial shifts. This also improved knowledge of several aspects of the natural history of recruits, in particular on feeding and survival rates. M. merluccius stock exhibited large variation in the year-class 0 strength. The location of the nursery area remained almost the same over the years, although noticeable differences in their size were observed. The changes in nursery area size seems directly correlated with the abundance observed during each season or year. An ontogenetic pattern of distribution was detected whereby age 0 fish are distributed almost exclusively at depths between 100 and 250 m, intermediate ages (mainly composed by 1-year-old individuals) are concentrated in more shallow waters while older individuals generally are found in the slope of the continental shelf. A better knowledge on changes in time and space of nursery areas location and of fish density and biomass will allow a more sound management of the resource. (C) 2004 Elsevier B.V. All rights reserved.