Bathymetric trends in distribution and size of demersal fish species in the north Aegean Sea

Abstract

Seasonal experimental trawl surveys (summer 1990–winter 1993) were carried out in the north Aegean Sea, at depths from 16 to 500 m. A total of 192 demersal fish species was caught. Bathymetric distribution of the dominant species was investigated using the quantitative model of the “centre of gravity” (COG) and habitat width (HW), a measure of the distribution heterogeneity. Out of the 40 dominant species studied, 31 were fully included within the range of available depths and most of them were centred between 90 and 270 m. The analysis indicated that most of the species exhibited a wide distribution range within the study area, although few were restricted to the greatest depths. Size‐depth trends of the dominant species demonstrated significant positive relationships for most species (56%) examined. The average rate of increase in fish length with increasing depth was also estimated, while correlation analysis was performed between mean depth and minimum or maximum fish size. The results indicated both a tendency towards “larger‐deeper” and “smaller‐shallower” for most of the species, depending on the size range of different species, but the larger‐deeper trend predominated.

Keywords:

• demersal fish
• centre of gravity
• habitat width
• species diversity
• size‐depth trends
• northeastern Mediterranean

Acknowledgements

The authors thank all those involved in demersal trawl surveys in the northern Aegean and Thracian seas, carried out by the Fisheries Department of the National Centre for Marine Research, for their valuable help. This work was partially supported by the EU, DG XIV under the Contract No MA‐1‐90, and the Greek General Secretariat for Research and Technology.