A trawling vessel is provided with a trawl net (5) for catching marine bio-resources, with a trawl sack (3) attached aft on a trawl net (5) for keeping the catch. The vessel comprises lines (51, 61) for towing and hauling the trawl net (5), and trawl drums (6) for hauling the trawl net (5). A lock chamber (1) is provided in a stern (21) of the vessel and has a main portion of its volume arranged below the design water line of the vessel. The lock chamber (1) is arranged for hauling the trawl sack (3) with the catch from the sea through a sluiceway (2) in the stern (21), for discharging the trawl sack (3), and for temporarily keeping the catch. A trunk channel (16, 12) leading up from the lock chamber (1) enables the trawl sack (3), in a generally discharged state, to be hauled up through the trunk channel (16, 12) to a deck (24), thereby leaving the catch in the lock chamber (1).