Bycatch Reduction Devices in Rio Grande do Sul, Brazil
 Open drag with sediment sample in Patos Lagoon Estuary |
The shrimp trawl fishery is responsible for producing one of the major bycatch rates worldwide, which is currently associated to the small mesh size and the use of boards. In southern Brazil, there are two types of shrimp trawl fisheries, small-scale fishery, mainly done in estuaries, and industrial double-rig fisheries. Trawling fisheries may reduce macrobenthic densities but not their vertical stratification. The impact of trawling on key species may compromise the ecosystem function, as benthic macrofauna provide food sources for many aquatic resources. To evaluate the impact of small-scale trawl fisheries on the macrobenthic fauna, experimental trawls were carried in two areas of the Patos Lagoon Estuary. Bottom images with side scan sonar were recorded before and after trawling to evaluate the marks left by trawl gears. The trawling impacts on the macrofaunal densities and assemblage structure were mainly detected in the area with higher percentages of fine sediments. The marks left by trawl gears were deeper and remained continuous in almost the whole track of the net in the area with finer sediments, while track immediately filled up on the sandy area. Some decreases on total macrofaunal densities after trawling were observed, mainly on the superficial stratum, and signs of burial activities. The response to trawling disturbance of each species was different and it highly depended on their natural variability.
 Sediment sample being sectioned to a posteriori analysis of vertical stratification |
On another front, to promote the use of fyke-nets, which are legal in the Patos Lagoon Estuary, instead of trawl nets, to capture pink shrimp (Penaeus paulensis), technical improvements were attempted to improve the fyke-net selectivity. These improvements are important due to recent surveys indicating that an average of 44% of what is captured in this fishery is bycatch. To improve the selectivity of these nets, the efficiency of a Fisheye BRD for the exclusion of bycatch was tested. Preliminary results point to a significant reduction of bycatch ratio (control: 1:2.8 and fisheye: 1:1.9). Currently, more tests are being carried out to determine what are the best position of these BRD in order to reduce the bycatch of fish without significantly impacting the capture of the target species.
In the Southern Brazil coast, the industrial shrimp fishery is composed for almost 160 vessels, between 15.5 and 22 m. The bycatch in this fishery was analyzed and through the morphological analysis of the species collected an ideal square-mesh size for trawl nets was estimated. In addition, a square-mesh codend was tested in a semi-industrial shrimp trawl fishery in Balneario Camboriu city. The preliminary tests did not indicate a significant reduction in bycatch ratios. However, the data need to be more deeply explored, since most of the catch was composed by crabs, which are not expected to escape through the square mesh panel. The tests are still continuing.
 Fisheye in a small-scale fyke net in Patos Lagoon Estuary |