Workshop on the Further Development of the New IBTS Gear (WKFDNG)

The standard gear for the International Bottom Trawl Survey (IBTS), a fisheries-independent research survey originating from the 1960s, will be replaced. The long-term monitoring provides data on commercial pelagic and demersal fish species for stock assessments and facilitates examination of changes in fish distribution and abundance. The remit of this Workshop on the Further Development of the New IBTS Gear (WKFDNG) was to design a simple gear, as standardised as possible, robust, and easy to maintain. Additionally, the workshop was tasked to provide input for the roadmap towards implementation of the new gear. In recent years, two new gears have been developed. Both are demersal otter trawls, modelled in line with current commercial fishing nets, and taking into account the needs for IBTS. Test runs, comparing gear operation as well as catches, have been conducted. The evaluation of new gears has been used as the starting point for the new design. The most important elements for evaluation were the ease of handling the gear on board, simplicity of building and maintenance of the net, physical robustness, stable net geometry, and suitability for catching the current target species. As a result of this evaluation, WKFDNG prepared three net plans describing the construction of the net, including the number of meshes in the different net sections, and the mesh sizes applied. The net plans have been standardised towards the crucial elements defined by the workshop. As a next step, the International Bottom Trawl Survey Working Group (IBTSWG) will consider adopting one of the net plans for further use in (North Sea) IBTS, based on the key choices specified in this report.For the lower front part of the nets, the part touching the bottom, two new ground gears are proposed, a light hopper and a clean ground gear, that are needed in different areas due to the different habitats. The light hopper rig will serve as a replacement for the bobbin rig currently being used exclusively in the Scottish IBTS survey, and is also suitable for other rougher areas in regions outside the North Sea. The proposed clean ground gear can be used in a larger area than the current clean ground gear. By adopting these two ground gears, the number of different ground gears in the IBTS can be reduced from four to two. Input is also given on a number of other topics, such as the use of restrictor ropes and/or autotrawl systems to stabilise net geometry. Furthermore, a change of speed range, and the standard unit for trawl length (distance instead of duration) was discussed. Lastly, the workshop also provided input for the transition period from the current gear towards the new gear.