Retained catches of trawl fleet in Chalkis fishing port-market, Greece, were analysed using generalized linear models (GLMs) in an attempt to identify factors that influence the total landings of the groundfish fisheries. Main effects in the model included a factor for vessel tonnage that determined fishing power, as well as factors for month and fishing area. Covariates examined were all found to have a significant effect on the retained catches, with month and vessel capacity alone explaining 38% and 30% respectively of the total variation of the data. Significant interactions observed indicate that the fluctuations in retained catch differed by fishing area and month as well as by fishing area and vessel category. Within vessel categories, month and fishing area also had significant effects on the retained catches, with fishing area being more important than month for the smallest vessels. Results indicate that the modelling approach of retained catches from trawl fisheries is a promising method for obtaining representative abundance indices.