Effects of fishing on marine ecosystems are concern throughout the world. Bottom fishing, especially employing towed fishing gear such as shrimp trawl, is considered as major sources of discards and habitat disturbances. Many kinds of by-catch reduction device (BRD) has been tested in the world as a possible counter measure for mitigating discard issues. In order to develop BRDs, we consider that verification of separation function of BRDs is important which suits specific objectives of fisheries management. Quantitative assessment methods such as the contact probability modelshould be employed for this purpose. Regarding measures aimed at reducing the physical impact of towed fishing gear on the seabed environment. We also introduce studies on the environment-benigntowed fishing gear in Japan. These gears are still in the developing stage because considerable degree of catch reduction was reported while they reduced physical impacts on seafloors. Future research will focus on optimizing these gears to reduce catch reduction while minimizing the damaging effect of towed fishing gear on the seafloor environment.
