Commercial trammel prawn nets were used during 40 nights at various phases of lunar months during May-October, 2002 period in Izmir bay (Aegean sea). The most dominant eight bycatch species and one target species (Melicertus kerathurus) (by numbers per fishing day) were used in the statistical analyses to compare the differences in catch numbers within each species during a standart lunar month. Using the Kniskal-Wallis test significant (p<0.05) differences in mean catch rates between moon phases were exhibited by Melicertus kerathurus (p = 0.011), Bolinus brandaris (p = 0.001), Squilla mantis (p = 0.041) and Mullus barbatus (p = 0.033). In contrast, Goneplax rhomboides, Diplodus annularis, Arnoglossus laternu, Microchirus variegatus and Solea solea showed no significant differences in catch numbers according to moon phases. Results suggest that target species and some of the most dominant bycatch species exhibit behaviour related to lunar cycle with implications for sustainable management.