495 



Abstract— The patterns of distribu- 

 tion and feeding habits of juvenile red 

 porgy, Pagrus pagrus. were studied for 

 fish collected in experimental trawl sur- 

 veys carried out along the Cretan con- 

 tinental shelf over a period of four 

 years. Abundance increased signifi- 

 cantly in shallow waters, with a maxi- 

 mum between 20 and 50 m for all sea- 

 sons, negatively correlated to depth and 

 positively correlated to temperature. 

 Patterns of bathymetric distribution 

 were similar for all sizes of juvenile red 

 porgy, varying little among seasons. 

 The fact that no specimens larger than 

 219 mm FL were caught in the trawl- 

 able fishing grounds indicates that 

 larger individuals aggregated over 

 hardbottom areas that could not be 

 sampled by trawling. Feeding intensity 

 varied among the size classes of fish 

 examined. Stomach-content analysis 

 revealed that juvenile red porgy are 

 carnivorous, feeding mainly on deca- 

 pods. Diet composition did not vary sea- 

 sonally; decapods were the most impor- 

 tant prey throughout the year. How- 

 ever, the composition of the prey con- 

 sumed varied considerably with preda- 

 tor size, coupled with differences in 

 mean prey sizes found in each size 

 class. Feeding rates of juveniles in 

 terms of both feeding intensity and 

 amount of food consumed were high 

 and increased with fish size. The 

 Cretan continental shelf habitat offers 

 increased growth rate, reduced preda- 

 tion risk, and increased food abundance 

 to juveniles and therefore they direct 

 energy entirely into somatic growth. 

 Juvenile red porgy appeared to be a 

 separate unit, from a management as 

 well as from an ecological point of view. 

 Habitat segregation is of importance; 

 juvenile specimens were differentiated 

 from mature fish on the basis of their 

 selection of bottom type and prey and 

 to a lesser extent by depth. 



Habitat selection and diet of juvenile 



red porgy, Pagrus pagrus (Linnaeus, 1758) 



Mary Labropoulou 



Department of Biology 



University of Crete 



PO Box 2208, GR-71409 Iraklion, Crete. Greece 



Present address National Center for Marine Research 



Agios Kosmas, 166 04 Hellinikon, Greece 

 E mail address mlabrogposidon ncmrgr 



Athanasios Machias 



Institute of Marine Biology of Crete 



PO Box 2214, GR- 71003 Iraklion, Crete, Greece 



Nikolaos Tsimenides 



Department of Biology 



University of Crete 



PO. Box 2208, GR-71409 Iraklion, Crete, Greece 



Manuscript accepted 20 August 1998. 

 Fish. Bull, 97:495-.507 ( 1999). 



Spatial and temporal variation in 

 population attributes, size and age 

 structure, abundance and distribu- 

 tion, generally reflect life history 

 properties of a species. Changes in 

 diet or habitat (or both) during on- 

 togeny are extremely common in 

 fishes (Werner and Gilliam, 1984). 

 Fish partition food resources be- 

 tween species as well as between 

 size classes within a species. Simi- 

 lar mechanisms such as differences 

 in morphological features, foraging 

 behavior, period of activity and 

 habitat use. affect segregation of 

 resource use in both cases (Werner, 

 1979; Mittelbach, 1981; Ross, 1986; 

 Norton, 1991 1. However, different 

 ecological processes have been em- 

 phasized in interpreting the adap- 

 tive value of resource partitioning 

 in these two situations. Partition- 

 ing among species has been argued 

 to reduce interspecific competition 

 (Sale, 1979; Osenberg et al., 1992; 

 Schluter, 1994). By contrast, differ- 

 ential vulnerability to predators or 

 the ability to exploit prey (or both) 

 may lead to de facto partitioning of 

 prey among age classes within a 

 species, with the consequence that 

 intraspecific competition is reduced 

 (Werner etal., 1983). Many fish un- 



dergo ontogenetic changes in prey 

 use between young-of-year and 

 older stages. Both the ability to uti- 

 lize the full spectrum of prey and to 

 escape predators may be highly size 

 related. Apart from changes in for- 

 aging demands, the vulnerability to 

 predators decreases with increasing 

 body size. Smaller fish frequently 

 use sheltered habitats to reduce 

 predation risk, whereas larger fish 

 are often found in unprotected ar- 

 eas (Miller, 1979; Werner and Hall, 

 1988; McCormick, 1989).As a result 

 of these changes in life style, fish 

 may occupy different niches during 

 ontogeny (Liem, 1984; Werner and 

 Gilliam, 1984). 



The red porgy, Pagrus pagrus 

 (Linnaeus 1758), is a protogynous, 

 sublittoral, demersal marine fish 

 associated with a variety of temper- 

 ate to subtropical habitats in the 

 Atlantic and the Mediterranean 

 Sea. It is commonly found on sandy, 

 gravel, and hard bottoms, or around 

 rocks, at depths ranging from 18 to 

 185 m (Manooch and Hassler, 1978; 

 Vaughan et al., 1992). The correla- 

 tion of age with maturity suggests 

 that the majority of the females 

 reach sexual maturity at three 

 years (Manooch, 1976; Pajuelo and 



