Effects of different by catch reduction devices (BRDs) in shrimp trawlers in the Persian Gulf

Abstract

The effect of different bycatch reduction devices in decreasing bycatch of commercial fish species with the length of less than LM50 (the length from which, 50% of them are matured) in shrimp trawlers were examined. The experiments were conducted in Persian Gulf (Bushehr and Hormuzgan provinces) during the shrimp season, years 2000-2001. In this study four types of bycatch reduction devices (Grid, Nafted, Fish eye and Square mesh window) were used. Double rig trawl was used, one of them as an experimental trawl and the other as the control. Different treatments like one device or two devices were installed on experimental shrimp net. After hauling the trawl, frquency of different commercial species with length less than LM50 was determined in both nets, and the results were tested with Paired Willcoxon test. The results have shown that although all the devices have a reductional effect on bycatch of the young and juveniles of commercial species, but the amount of reduction with setting Nafted and Grid, either single or combined with another BRD was significantly higher than the control one (P ≤ 0/05). The amount of by catch reduction devices with different treatment (different devices either single or paired) according to the season of the experiment were also tested with Kruskal- Wallis test, which shows significant differences (P≤0.05) between the frquency of young and juvenile individuals of some species during different experimental seasons. According to this study, by using Nafted and Grid devices in the trawl nets of all shrimp vessels during its season, about 400 to 500 thousand of juveniles and young individuals can escape from the nets.