Back in March 2017, Ben Collier introduced the industry-led collaborative project: The Northern Ireland Gear Trials project. As well as experimenting with lights in trawls to increase the selectivity of target species, Ben and his team have also been working on other novel gear design approaches. Now, Ben is back to update us on the preliminary results from his trials and let us know what’s coming up next…
During March and April of this year, four separate trials were undertaken on board twin-rig and single-rig Nephrops trawlers operating in area VIIa. The project has collected and analysed data on the performance of several different selective devices, two of which having been first trialled in 2017.
The selective gears that were trialled most recently are a 90mm codend and extension against an 80mm codend and extension (twin-rig), 90mm codend and extension against 70mm codend and extension (single-rig), the Fin Fish Free design (FFF) and the Inclined Net Grid design (ING). Both the FFF and ING designs were previously trialled with lights fitted to the square mesh panels of each trawl. During this trial period, the lights were repositioned inside the trawl directly onto the active selective component of each design. Twin-rig vessels were used for the FFF and ING trials. The effects of introducing a 90mm codend/extension on discard rates and Nephrops capture were assessed in response to suggestions provided by the commission.
Results from 90mm trials
The data collected from both 90mm trials indicated that the increase in mesh size had a significant effect on reducing the capture of fish species with reductions of whiting of -51% when compared to an 80mm codend/extension and -65% when compared to a 70mm codend/extension. Reductions in catch were also apparent and significant for Nephrops. Based on the data collected during these trials, reductions in Nephrops catch of -31% and -53% were noted for the twin-rig and single-rig vessels respectively. Although this trial showed the 90mm codend/ext was efficient at reducing white fish it would not be viable in the Irish Sea Nephrops fishery due to the excessive loss of commercially valuable catch.
Results from the FFF & ING trials
In our last set of trials in March, we illuminated the square mesh panels (SMPs) of the trawls. This led to more bulk in the codend, we thought this could have been caused by the lights on the SMPs discouraging fish from swimming through them and out of the gear. So, this time around we placed the lights on to the active selective component on the FFF & ING as we hoped it would encourage an upward movement of fish towards an exit point on top of the trawl.
Overall, we were partially pleased with the results from the ING trial as it seemed effective at reducing fish, especially below minimum conservation reference size (MCRS) whiting, which is a key issue that we are attempting to address here in Northern Ireland. Analysis of this data showed reductions of whiting of -35%. However, the loss of Nephrops (-26% Nephrops) with this design was disappointing, but we have collected some good advice on ways to correct this.
The FFF design produced a mixed set of results with no clear indication that this design is effective at removing fish from the trawl whilst retaining the Nephrops catch.
The next phase
During the next phase of trialling, which has been scheduled for August 2018, the ING will be trialled again with the lights removed this time. In addition, a modified ING trawl will be manufactured and trialled with a 400mm net grid fitted instead of a 200mm version that was previously trialled in March. The expectation is that an increased mesh sized grid will allow more Nephrops to pass through it and continue through to the codend.
In addition to both version of the ING designs, a further trial will aim to assess the effectiveness of a SELTRA box trawl at reducing the capture rate of unwanted quota species and juvenile fish species.
Overall, we are pleased with the progress so far, and even though we’ve had trials that haven’t gone well, the fishermen trialling the gear understand that negative results are just as useful as positive results – they appreciate that gear trials are as much about identifying what doesn’t work as what does. The fishermen we work with are constantly re-setting their gear so it’s in their nature to play about with things that appear not to work at first. We are looking forwards to the next set of trials now, and I’ll keep you updated.
Stay tuned for more updates from Ben soon.