A fishing net for a set-net is often covered with marine foulings while operating. We attempted to measure a drag on the fouled nets. The test nets were soaked in a set-net fishing ground during the periods from 15 to 60 days and some water depths (1.5 to 15 m). The test nets consisted of polyester multi-filaments (0.85 mm in diameter and 17 mm in bar length), which is commonly used for the set-net fishing gear. The main marine foulings are fine attaching materials so-called 'Nuta', Amphipoda, a kind of hydroida Tubulalia mesembryanthemum and a kind of moss animals Bugula neritina. The drag per 1 m2 for each test net at the right attack angle and 0.5 m/s in flow velocity was from 3.7 kgw to 19.3 kgw. The changing ratio of drag varied from l.4 times to 8.5 times against the initial (unused) net. The mean ratio of drag on each socking period, however, peaked 6.5 times of the 30th days net and then it scarcely changed til1 60th days net.
