This study attempted to determine certain characteristics of the species caught in the boat seine fishery in the Istanbul Strait during the 2009-2010 fishing season, including catch composition, commercial and nontarget catch ratios, catch per unit effort (CPUE), and the length distributions of commercial species. A survey of 20 boat seine operations detected species belonging to the following 3 different taxonomic groups: 26 Osteichthyes, 2 Crustacea, and 1 Mollusca. Of all of the nontarget species, 13 were commercial, 14 were noncommercial, and only 1 was under threat. Of the total catch, the proportion of the commercial species in the nontarget catch was 31.3%, and that of the discarded catch, which the fishermen did not take into account, was 2.8%. According to the Spearman rank correlation test, there was a significant correlation between the total catch and the discarded catch (r = 0.759); the size of discarded catch increased as the catch increased (P = 0.000). It was clear from the data that overfishing was seen in the commercial species.