Fisheries Research 81 (2006) 60–71 Comparison of demersal ﬁsh assemblages in three areas of the Strait of Sicily under different trawling pressure M. Gristina a,∗ , T. Bahri b , F. Fiorentino a , G. Garofalo a a IAMC-CNR, via L. Vaccara 61, 91026 Mazara del Vallo (TP), Italy b FAO-MedSudMed, via L. Vaccara 61, 91026 Mazara del Vallo (TP), Italy Received 27 October 2005; received in revised form 27 April 2006; accepted 14 May 2006 Abstract The effect of trawling on demersal ﬁsh assemblages was measured in an experiment involving repeated trawling in the Strait of Sicily. Three areas were chosen according to their exploitation level by commercial trawl ﬁshery: practically unexploited by the commercial ﬁshery (area C), subject to light and recent ﬁshing pressure (area L) and heavily exploited by commercial trawl ﬁshery (area H). Data were collected during two scientiﬁc surveys carried out in autumn 1997 and 1998; temporal replication was used to conﬁrm the observed spatial pattern. The status of the demersal ﬁsh communities in the three areas was compared using a variety of approaches and a number of community metrics (cluster analysis, similarity percentage analysis, ANOSIM pairwise test, size spectra, diversity indices). Results indicate that abundance, species composition and size-structure of the ﬁsh community in area H are different from the other two areas. Differences between area C and area L are small and concern mainly the relative abundance of some species. Eventually, the results show how ﬁshing can substantially shape the ﬁsh communities in the three areas. © 2006 Elsevier B.V. All rights reserved. Keywords: Trawl ﬁshing impact; Fish community structure; Strait of Sicily 1. Introduction Over the last decade, both ﬁshery science and ﬁshery man- agement shifted their concern from populations to ecosys- tems (Hall and Mainprize, 2004). Fishing-induced changes on marine ecosystems are wide-ranging and comprise both direct (abundance decrease, changes in size and species composition, modiﬁcations of population parameters), and indirect effects (trophic shift, bottom disturbance) which act on short and long-term temporal scales (Pauly et al., 1998; Jennings et al., 1999; Stevens et al., 2000). These effects have been documented using a variety of methods and com- munity metrics including multi-parametric analysis, diversity indices and size-based indicators (Rice and Gislason, 1996; Hall and Greenstreet, 1998; Hall, 1999; Rochet and Trenkel, 2003). A number of studies attempted to identify the most relevant ecological indicators to better detect ﬁshing effects; ∗ Corresponding author. Tel.: +39 0923 94 89 66; fax: +39 0923 90 66 34. E-mail address: michele.gristina@irma.pa.cnr.it (M. Gristina). they all stated that a set of indicators rather than a single one is needed to describe the full range of ﬁshing-induced changes (Trenkel and Rochet, 2003). Despite many relevant results and some promising perspectives, a major problem derives from the lack of pristine areas. These latter could allow to select unequivocal biological reference points for a better understanding of the re-organisation of ﬁsh communities in response to ﬁshing (Steele and Schumacher, 2000). Trawling in the Strait of Sicily began in the early 1900 but becomes intensive after the 1970. In particular, the Mazara del Vallo trawl ﬁshery (south-western Sicilian coast), is one of the most important in the Mediterranean Sea (about 180 trawl vessels). The 21% of the trawl ﬂeet (mean GRT = 76) operates in the Sicilian coastal waters with short ﬁshing trips (1–2 days); the remaining 79% of the trawl ﬂeet is characterised by boats up to 105 GRT that make deep-sea ﬁshing and carry out long trips (21–25 days) in the Strait of Sicily. It has heavily exploited the demersal resources of the Strait of Sicily, causing their slow decline (Levi et al., 1998). Although there is evidence of overﬁshing for single target 0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ﬁshres.2006.05.010