A global review showed four broad categories of mitigation used during longline hauling: physical barriers, measures that reduce the attractiveness of the haul area, deterrents, and operational approaches that are part of fishing. Of devices that operate as physical barriers to seabirds, bird exclusion devices, tori lines and towed buoys have been tested and proven effective in reducing seabird interactions with hauled longline gear. Discharging fish waste such that seabirds are not attracted to the hauling bay is another effective measure, and seabird abundance around vessels is reduced by retaining fish waste during hauling. While a number of deterrents and ad hoc or reactive approaches to reducing haul captures have been discussed in the literature (e.g. water sprays), these have generally not been empirically tested.
Information collected by government fisheries observers on 73 bottom longline and 60 surface longline trips that have occurred since 1 October 2012 on New Zealand vessels < 34 m in overall length showed that most of these measures are in place here. However, implementation may be limited to a small number of vessels (e.g. one bottom longliner used a tori line and two surface longliners used a buoy to reduce seabird interactions with gear at hauling). Implementation may also not be consistent amongst vessels in a fleet, or on the same vessel between trips (e.g., for fish waste management, where some skippers retained all waste until after hauling or discharged when hooks were well below the sea surface, whilst others discharged used baits directly back into the hauling bay as the line was pulled in). This variation in practices creates consequent variation in haul capture risks. Further, the information already available on vessel operations in New Zealand is sufficient to enable actions to reduce haul capture risks.
Recommended next steps to progress haul mitigation work in smaller-vessel bottom longline fisheries includes prioritising mitigation efforts in FMA 1, given the relatively large numbers of captures of high risk seabirds reported there. For surface longline fisheries, a fleet-level approach is recommended, given vessels are often mobile amongst FMAs due to the highly migratory nature of target fish species and relatively smaller number of vessels involved (less than 40). Mitigation efforts should include exploring device deployments (e.g. buoys) to reduce haul captures, and improving the quality and consistency of fish waste management practices that minimise capture risks during hauling. Recommendations are also provided for enhancing data collection to improve knowledge and understanding of the nature and extent of haul captures in New Zealand’s smaller-vessel longline fisheries.
A trip to sea on a vessel targeting bluenose with bottom longlines was used to test 'barrier' and 'dangler' approaches to reducing interactions and seabird abundance at the hauling station. Following initial setup and refinement a 'dangler' was chosen for quantitative testing over seven days' fishing. The dangler comprised of a single solid dropper with a 150mm diameter float on the water surface 1.8 m from the side of the vessel and 2 m astern of the hauling station.Trials invloved switching between no mitigation and a 'dangler' treatment within hauls. Real-time data included bird abundance within 100m of the vessel, within two metres of the longline and within two to five metres of the longline. Counts were also made on the number of birds enetring the areas close to the longline in 5 minute observation periods. Analysis of video footage collected at the hauling station provided counts of birds within 2 m of the hauling station during consecutive 10 second periods throughout hauling.No seabird bycatch (alive or dead) was observed during the trip.
Whilst abundance within 100m of the vessel was simialr between treatments the dangler device reduced bird abundance in the danger area around the longline, compared to the no mitigation treatment.Video footage and real time counts showed similar responses. The continuous coverage afforded by reviewing video footage provided a more comlete picture over time, however real-time data allowed for a better assessment of the 'danger area' relative to the longline, and provided a more complete summary of fishng operations.The dangler fitted into the fishing operation with little or no disruption to normal fishing practices, and the skipper and crew were willing to continue using it. Fishers are most likely to incorporate specific hauling mitigation devices if they fit around their current fishing operation, and are easy to deploy and recover.A large number of variables influenced interactions between birds and fishing gear during the haul. Combined with a single trip, in a single area, and without aggressively foraging birds these variables limit the certainty around these results. Similarly, with a small data set it was not deemed appropriate to attempt to quantify efficacy of the device.
Goad, D. 2018. Small longline vessel hauling mitigation development. Final report prepared by Vita Maris for the Conservation Services Programme, Department of Conservation, Wellington. 15 p.
Pierre, J. 2018. Mitigating seabird captures during hauling on smaller longline vessels. Final Report prepared by JPEC for the Conservation Services Programme, Department of Conservation, Wellington. 47 p.