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Fishery Bulletin 97(3), 1999 



Lorenzo, 1996; Harris and Mc- 

 Govern, 1997 ). The red porgy is of 

 great commercial importance and 

 consequently a highly exploited 

 species in the areas of its distri- 

 bution (Manooch and Hassler, 

 1978; Stergiou and Pollard, 1994). 

 It is one of the most promising 

 new species for fish farming in the 

 Mediterranean Sea, having re- 

 markably high growth rates un- 

 der intensive rearing conditions. 

 Therefore, the ambient demands 

 of young individuals are of special 

 interest for aquaculture (Divanach 

 et al., 1993). The young individu- 

 als are distributed inshore of the 

 adult population in trawlable ar- 

 eas. Even though they occur in- 

 shore as juveniles, adverse condi- 

 tions of low water temperatures, 

 competitive exclusion and unsuit- 

 able substrate reduce the longev- 

 ity of this inshore distribution. 

 Adult red porgy do not occur in the same shallow 

 waters as those inhabited by juveniles. The larger 

 fish predominate in deeper waters, preferring hard 

 substrate ( Manooch and Hassler, 1978 ). A general trend 

 for larger fish to occur in deeper water has long been 

 known with respect to deep sea fishes (Haedrich and 

 Rowe, 1977); however it has also been mentioned by 

 Macpherson and Duarte (1991) for many demersal 

 fishes of the continental shelf Caddy ( 1993 ) has stated 

 that offshore movements of older fish to locations on 

 untrawlable bottoms possibly contribute to the continu- 

 ing good recruitment, as well as to the stock recovery. 

 The aim of the present study was to define the 

 habitat use of juvenile red porgy along the Cretan 

 continental shelf and to examine whether red porgy 

 undergo considerable changes in resource utilization 

 during ontogeny. In addition to determining bathy- 

 metric trends in mean size of red porgy, the relation- 

 ship between density, depth, and temperature within 

 size groups are defined. Furthermore, we investi- 

 gated the effects of the feeding habits, prey choice, 

 and trophic interactions among the different size 

 groups on the distribution patterns of red porgy. 



Material and methods 



Study area and sampling procedure 



A three-year survey on the distribution of red porgy 

 was carried out along the Cretan continental shelf. 



Figure 1 



Location of the sampling stations on the Cretan continental shelf. 



from August 1988 to April 1991. Nine seasonal ex- 

 perimental bottom trawl survey cruises were con- 

 ducted by the Institute of Marine Biology of Crete at 

 40 fixed sampling stations selected to cover all the 

 trawlable fishing grounds of the region (Fig. 1). The 

 collected data included abundance of fishes caught 

 and supporting data on depth, temperature, and sa- 

 linity. The cruise periods were as follows: late Au- 

 gust to early September (summer), December (win- 

 ter), and late March to early April ( spring). The sam- 

 pling stations were distributed over three distinct 

 depth zones: 26-70 m (zone I), 71-150 m (zone II), 

 and 151-350 m (zone III). Zone I covered 25%, zone 



II 24%, and zone III 51% of the total study area. Al- 

 gae and marine angiosperms, mainly Caulerpa 

 prolifera , Posidonia oceanica, and Halophila stipulacea. 

 dominated the sand-silt substrate in zone I. The sub- 

 strate of zone II was muddy and the substrate of zone 



III was covered by the crinoid Leptometra phalan- 

 gium. Monthly samples (excepting January) from 

 August 1990 to August 1992 were also taken from 

 experimental trawl surveys in Iraklion Bay for stom- 

 ach-content analysis. These samples were collected 

 from a fixed station on the trawlable fishing ground 

 of the region between 25 and 35 m during the morn- 

 ing, between 0830 and 0930 hours. 



The trawl used was equipped with a codend bag 

 liner of 22-mm stretched mesh size. The duration of 

 each haul (bottom time) was 50-90 min and the 

 trawling speed fluctuated from 1.8 to 3 knots, de- 

 pending on the depth and nature of the bottom. Be- 



