|Equipment Class: Fishing technology||Equipment Type: Environmental measures|
|Bycatch Reduction Devices (BRD) are devices inserted in a fishing gear usually trawl in shrimp fisheries, close to the cod-end, to allow escapement, alive, of unwanted species (including medusae) or individuals (juveniles) or endangered species (e.g. seals, turtles, dolphins). |
Most BRDs rely on one of two methods of excluding bycatch. The first is mechanical or physical exclusion, achieved by blocking the passage of bycatch into the codend and guiding it towards an escape opening. This is the most common method of excluding large animals from prawn trawls. The second method utilises differences in behaviour between the bycatch and prawns. Fishes for example, are capable of swimming in a moving net, orientating to the direction of tow and swimming through an escape opening. Prawns on the other hand generally exhibit little directional swimming and are passively filtered into the codend. The reduction of bycatch has the potential to improve the efficiency of the fishing operation because:
The gear would stay on the bottom longer and time wasted during deployment and hauling would decrease.
Otter board spread may be maintained for longer periods.
Net damage from large animals would be reduced.
Sorting time may be shortened.
Injuries to crew from dangerous animals might be reduced.
The initial choice of BRD depends on the type of bycatch that fisherman wants to exclude. The choice of BRD is made more difficult by variations in catch composition, size and type of prawn and bycatch, and amount of bycatch caught throughout the season and between fishing grounds. For this reason more than one BRD or configuration may be required to maximise bycatch reduction during the fishing season.