The distributions of 2 congenerics, sympatric species of Mullidae (Mullus surmuletus and M. barbatus) were studied by means of abundance and length frequencies, obtained in experimental trawl surveys carried out in the springtime (1994 to 1998) throughout the Spanish Mediterranean area. From the data obtained we compared the spatial segregation between these species in relation to the bottom type and to the depth of their habitat. Although M. barbatus was the most abundant species throughout the sampling area (except at the shallowest rough-bottom sites), spatial segregation was observed between the 2 species, with the ratio between the species varying according to the bottom type on which they lived. M. barbatus showed maximum abundance and frequency on muddy bottoms in waters between 50 and 200 m deep. For M. surmuletus, maximum density and frequency were at a shallower depth (between 10 and 50 m) and largely on rough bottoms. At overlap sites, the relative abundance of M. barbatus increased on muddy bottoms and decreased on rocky and sandy bottoms. The size frequencies encountered for both species were made up by preadults and adults. Significant size differences between species existed in all the bathymetric strata studied. In all cases, except the more coastal muddy bottom stratum, M. surmuletus had a range of sizes and a mean size greater than M. barbatus. The structural heterogeneity of the Spanish continental shelf gave rise to a distribution characterised by patches. M. barbatus had a clear preference for the areas where the shelf became wider, and M. surmuletus was more abundant and frequent in narrow shelf areas

11 pages, 4 figures, 5 tables

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