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¹ Mustafa Kemal University, Faculty of Fisheries and Aquaculture, 31040 Antakya, Hatay, Turkey Viewed : 4616 - Downloaded : 3087 For many marine surveys, a standard trawl is towed at each selected station over a period of time ranging from 30 minutes to as long as 120 minutes. A trawl towing duration experiment was conducted to determine whether different towing durations (60, 90, 120 and 150 minutes) had the same effect on the catch per unit of swept area (CPUE) of Saurida undosquamis, taking into consideration the variations in the CPUE among other members the Mullidae family (Mullus barbatus, Mullus surmelatus, and Upeneus moloccensis), Metapenaeus stebbingi, and non-target (by-catch) species. A simple random sampling technique was used for the survey sampling. The mean CPUE did not vary significantly with towing duration (P> 0.05) for the Saurida undosquamis catch. However, when towing was allowed to continue for 150 minutes, CPUE decreased dramatically while the CPUE values of the non-target species suddenly increased. The systematic decrease in the CPUE values along with the increase in the towing for Mullidae family turned out to result from predation by Saurida undosquamis on the Mullidae family as prey and also escape from the mesh due to gear saturation in the case of M. stebbingi. Gear saturation by non-target species and predator-prey relationship were among the possibilities considered as candidates for the main factors affecting the decrease in the CPUE values of the various species with increased towing duration. Thus, it was found through scientific surveys that after 120 minutes of towing, sampling on the economic catch was biased in the multi-species fishery of İskenderun Bay. The scientific surveys also demonstrated that short tows were at least as efficient as long tows for CPUE. Keywords : Towing duration, Saurida undosquamis, catch per unit of swept area (CPUE), bottom trawl survey