Northern Ireland selective trawl gear trial results

21st January 2019

study area

A process of formal and informal discussions was undertaken at the three main fishing harbours of Northern Ireland; Portavogie, Ardglass and Kilkeel. During the discussions, ideas were collected on how fishing gears currently being used for targeting nephrops can be modified or re-designed to increase the selectivity performance and improve the release of unwanted fish catch. In addition, several Northern Ireland and Republic of Ireland based gear manufacturers were also approached with the same requests for information and ideas. Selective gear designs were reviewed by an expert panel and subsequently approved or rejected before being taken forward to a manufacturing stage. In 2017 two novel designs were trialled at sea on board commercial fishing vessels over multiple trips with adjustments made each time. By early 2018, the analysis of results from the gear trials that had been run over the previous year of the project indicated that one design showed potential in addressing the project brief whilst the other showed less potential. The designs are named the Inclined Net Grid 200 and Fin Fish Free (FFF) trawls respectively. In addition to the two designs that were taken forward from 2017, the project assessed the potential selectivity attributes of attaching lights to various areas of gears. In March 2018 the square mesh panels (SMPs) of vessels trawls were illuminated with pressure activated light units. Three different colours/wavelengths of light were tested. The results from the light trials indicated that by illuminating the SMPs in trawls, more bulk catch is retained. This suggested that lights can be used to modify the behaviour of fish when caught in trawl gear however illuminating the SMPs seems to reduce the amount of fish that escape through it. Analysis of the results also indicated that whiting may be particularly affected by blue light, particularly individuals below MCRS. Subsequent trials repositioned the light units inside the Inclined Net Grid 200 and FFF trawls. The FFF trawl underperformed however the Inclined Net Grid 200 trawl with blue lights attached showed some potential. Fish release was high although nephrops loss was also affected. The project assessed the effect of increasing codend mesh size in the TR2 nephrops fishery with trials undertaken on board twin-rig and single-rig vessels. The results from this trial indicated that whilst an increase in codend mesh size from 80mm to 90mm may be effective at removing some of the fish component from the catch the loss of nephrops from both single and twin rig vessels was excessively high. Based on the results of data collected during trials of the two novel gear designs with lights attached inside, further trialling of the most promising gear design, the Inclined Net Grid 200, was undertaken with lights removed. In addition to this, a second section of trawl was manufactured to the same design with one key component modified to try and address the loss of nephrops that was observed during previous trials. In the new design the mesh size of the internal inclined net grid was increased from 200mm to 400mm square. This is called the Inclined Net Grid 400. The effect of increasing mesh size was successful in reducing the amount of nephrops that is lost from the trawl however the 400mm panel appeared to be less effective at removing fish from the trawl than the 200mm version. Finally, the project collected data on the performance of two currently approved TR2 highly selective devices. These were the 300SMP trawl and the SELTRA270 trawl. Analysis of the data collected over the duration of this trial indicated that fish release rates between the two selective devices are comparable however the SELTRA270 appears to be more effective at retaining the catch of nephrops. This could potentially be of conservation benefit. This report provides an overview of the work that has been undertaken by the Northern Ireland Gear Trials Project and provides summarised results on each trial for key species of interest.

escape panels and discussions

Discussion The forthright response from industry over the duration of the project has clearly indicated that ideas and suggestions on how gear selectivity may be improved exist within the Northern Ireland fleet of fishermen. The ideas that were collected tended to be relatively simple modifications to existing gear designs as opposed to truly new approaches to the catching process and this was mainly because fishermen understand that even a small change to a trawl can mean the difference between a profitable catch and catching nothing. EMFF support for the Northern Ireland Gear Trials Project has facilitated the development and trialling of some of these ideas and in addition has encouraged more thinking around how discards may be reduced in ways that have not been given much consideration before. Increasing the mesh size of codends & extensions is regarded as a simple approach to releasing more unwanted catch from a trawl however the data that was collected during this project indicated that increasing mesh sizes in the NI TR2 fleet of vessels may also have a negative impact on their nephrops catch. This was particularly evident when trialled on the single-rig vessels (appendix b). As under 12m vessels currently work to a minimum mesh size of 70mm the large increase to 90mm appears to be too great. It is likely that a contributing factor to this observation is the relative lack of engine power in the smaller fishing vessels. When engine power is insufficient to keep a continual longitudinal strain (drag) on the gear, meshes remain open over a larger proportion of the towing time. Results from the gear trialling of the Inclined Net Grid (ING) 200 and 400 versions provided clear indications that this design of trawl can remove a sizeable component of the fish catch from a nephrops trawl. The reduced nephrops catch, evident during the ING 200 trials was partially addressed by building and trialling the ING 400 however this version was not as effective at releasing fish (appendix b). Some further fine tuning of this design seems appropriate given the partially successful results achieved to date. The optimum size of square mesh netting from which the inclined panel should be made will need to strike a balance between encouraging fish to move up it whilst allowing nephrops of Irish Sea size to pass through it and onto the codend. See appendix C for net plan of Inclined Net Grid. There was a noticeable indication in the results that the introduction of lights to different areas of the fishing gears does produce differences in the catch of fish (appendix b). More research is needed to investigate the effects of light on the behaviour of different species as the data collected under this project suggests that fish behaviour can be influenced when inside the trawl. In most cases, from the data collected here, it appears to produce a deterring effect. Whiting for example appeared to be particularly deterred by blue light. Lights have shown potential as a new and novel way of improving the selectivity performance of a traditional trawl and the results of the trials suggest that where lights are placed in relation to the location of the escape point on a trawl is key. There are several currently approved, highly selective gears for use in the Irish Sea TR2 fishery (7) with the majority of Northern Ireland based fishermen opting for either a 200mm or 300mm square mesh panel dependant on the size of vessel. Trialling of the SELTRA270, another approved gear against the square mesh panel allowed some insight into the selective efficiency of each. Furthermore, useful data was also generated on the nephrops retention performance of each trawl. There was little difference in the fish catch over the duration of this trial, suggesting that fish release from the SELTRA270 and SMP trawls is comparable. Nephrops catch was greater in the SELTRA270 trawl appendix b). From this it may be inferred that this gear either fishes better than a SMP trawl or the SELTRA270 simply retains more of the nephrops catch. As the SELTRA270 trawl has a significantly reduced sized SMP as part of its requirements this may be an indication of nephrops loss through the more commonly used 300SMP trawl. It is apparent that there is no single solution to addressing the issues around discard reduction and meeting the challenges faced by full implementation of the Landing Obligation. A significant amount of work on gear selectivity has been carried out in Northern Ireland over the years and much progress has been made but the issue of below MCRS fish being caught in nephrops trawls remains.


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