||The high catch rate of small-sized trash fish from coastal trawls in Taiwan would bring a certain extent of impact on ecological resources. In order to reduce the high catch rate of small-sized trash fish caused by smaller mesh size of codend, this study designs the bycatch reduction device (BRD) in front part of codend. A number of experiments using the frame structure with vertical bars in different intervals and square mesh with different bar lengths of net were carried out in this study. The results are as follows:
?1. In different BRDs, the frame structure with vertical bars in different intervals has the significant filtering effects. But when the interval is over 15mm, the escaping rate of caught fish could reach over 50%
2. The number of fish species filtered into the upper codend with different experimental protocols could reach over 50% species number of original codend except that of vertical bars in 10mm interval. It indicates these experimental designs have the filtering effect.
3. The escaping rate of dominant species from upper codend in different BRDs showed that the frame structure with vertical bars in different intervals has the significant filtering effect while there is far interior to that of square mesh.
?4. From analyzing the body length frequency of different fish species it indicated that the selective effect had no significant difference among different BRDs and is difficult to find out the best interval by using selective curves. From above results it indicates that the selective effect of the design in the frame structure with vertical bars in different intervals is better than that of square mesh with different bar lengths of net.?When considering the costs and benefit of fishermen and sustainable utilization of resources, the design in frame structure with vertical bars in 13-15mm intervals is the more appropriate specification. However, before developing the trawl management policy, it still remains to advocate the concept of sustainable fisheries for fishermen and then gradually communicates with fishermen about the adjustment of management policies.