Pelagic Gillnet modification trials in Northern Australian seas

The selection and testing of a range of materials for use as passive acoustic modifications to deter dolphins from pelagic gillnets is discussed. Metallic bead chain and air-filled plastic tubing were selected for incorporation into nets for sea trials to assess the effect of the modifications on dolphin by-catch and fish catch. Trials using commercial gillnet vessels from Taiwan established that neither the bead chain nor the plastic tubing had a significant effect on the dolphin by-catch. Further sea trials compared the dolphin and fish catches of a gillnet set 4.5 m below the surface with a standard surface set net. A significant reduction in cetacean catch rate (cetaceans per set) was observed for the sub-surface net. The fish catch for both shark and teleost species was lower in the sub-surface net, with an overall reduction of approximately 25% in total fish catch. Data on the dolphin and fish catches for the trials are presented.