A study on length frequency distribution and trawl catch rate of red mullet by the subregions in the Aegean sea

In this study, bottom-trawl catch data and length-frequency distribution of red mullet (Mullus barbatus L.) were investigated in the Turkish waters of the Aegean Sea during 1991-1996. Trawl samplings were carried out by research vessel K. Piri Reis and a total of 341 trawls were hauled in the different areas of the eastern Aegean Sea. The study area is divided to five main sub-areas according to their ecological properties with three depth strata (A: 30-100 m, B: 100-200 m, C: 200-300 m.). Red mullet samples were grouped by these sub-areas for each sampling season and, average catch rates (kg/s) and biomass values (kg/km2) were estimated. These estimates were highly variable by the sampling sub-areas, strata and/or seasons, ranging from 0.07 kg/s and 1.59 kg/km2 (in the sub-area III and stratum B during summer 1991) to 18.13 kg/s and 431.64 kg/km2 (in the sub-area III and stratum A during winter 1994). In general, the catch rates and biomass estimates were found significantly lower in the North Aegean Sea than the other areas and an increasing trend was determined in these estimates from north to the south. The catch rates and biomass estimates were decreased with increasing depth and red mullet was rarely observed in deeper waters than 200 m. Length-frequency distributions of red mullet were also evaluated for each sub-areas, strata and seasons. Although, no significant difference was found in length-frequency distributions between the sub-areas, the ratio of smaller individuals in stratum A were higher than the other strata. There was no seasonal variation in the length-frequency distributions while smaller individuals were observed during autumn probably due to stock recruitment at this season.