Habitat selection and diet of juvenile red porgy, Pagrus pagrus (Linnaeus, 1758)

The patterns of distribution and feeding habits of juvenile red porgy, Pagrus pagrus, were studied for fish collected in experimental trawl surveys carried out along the Cretan continental shelf over a period of four years. Abundance increased significantly in shallow waters, with a maximum between 20 and 50 m for all seasons, 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 trawlable 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 decapods. Diet composition did not vary seasonally; decapods were the most important prey throughout the year. However, the composition of the prey consumed varied considerably with predator 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 predation 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.