Abstract
Two otter-board modifications designed to minimise bottom contact (and therefore habitat impacts) were compared against conventional otter boards for their relative effects on the engineering and catching efficiencies of triple-rigged penaeid trawls. The first modification involved restricting the angle of attack (AOA) of a flat-rectangular otter board to <30° by attaching a restraining line to an adjacent sled, while the second was a 'batwing' otter board comprising a sled-and-sail assembly operating at 20° AOA. The modifications reduced otter-board bottom contact by up to 8 ha over a night's fishing without affecting standardised catches (per ha) of the targeted eastern king prawns, Penaeus plebejus, nor the fuel required. Further, compared to all other trawls, the restrained trawls caught less discarded bycatch (by up to 37%), while the trawls spread by the modified flat-rectangular and batwing otter boards caught more individuals of three retained benthic teleost species per ha than the conventional configuration; results that were attributed to species-specific herding responses. Both modifications represent simple alternatives where there are concerns over either benthic impacts or, for the restraining line, unwanted bycatches in penaeid-trawl fisheries.
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