Relative benthic disturbances of conventional and novel otter boards and ground gears

A benthic trawl’s substrate contact (e.g. spreading mechanisms (i.e. otter boards) and ground gears) determines both its catching efficiency and the extent of perceived habitat impacts. The potential for mitigating habitat impacts was investigated here via the novel ‘batwing’ otter board and ‘soft-brush’ ground gear. A purpose-built testing assembly towed treatments across three artificial habitat types with incrementally greater detachment thresholds (~ 8, 32 and 56 N), and the batwing and soft-brush were alternately compared against a conventional flat-rectangular otter board and three chain ground gears (6-, 8- and 10-mm diameter link), respectively. Overall, during 48 alternate deployments, the batwing removed up to 61% fewer of all habitats than the flat-rectangular otter board. By comparison, during 42 alternate replicates, the soft-brush ground gear failed to displace any habitat, while all three chain ground gears similarly removed between 3 and 5% of the two least resistant habitats (irrespective of position). The results imply the perceived impacts of penaeid trawls across sensitive areas can be reduced via simple modifications to spreading mechanisms and ground gears, along with appropriate spatio-temporal regulation. This study represents a unique approach to understanding the relative differences in impacts between ground gears and commercial-sized otter boards under controlled conditions.