Industry-led trial on repurposed trawls demonstrates substantial improvements in Nephrops catch
rates, fuel efficiency and bycatch reduction
By Ronán Cosgrove and Matthew McHugh, BIM
BIMs Fisheries Conservation Sections works at sea onboard commercial fishing vessels in close
collaboration with the fishing industry to address key environmental and related economic issues.
Most of our gear trials are focussed on reducing unwanted catches or bycatch, improving carbon and
fuel efficiency, while maintaining commercial viability. We regularly make gains in two of these areas
but technical solutions which hit the mark on all three are rarer events.
Thomas Whelahan, owner of the MFV Cisemair had some spare trawls following decommissioning of
another vessel and was keen to try modifying them to improve fuel efficiency. Reduced twine
surface area from increased mesh size is known to reduce hydrodynamic drag. Previous BIM trials of
four-panel ‘box trawls’ with extensive sections of enlarged mesh in the top sheet demonstrated
substantial improvements in energy efficiency but ultimately requires purchase of new nets.
Modifying existing two-panel nets potentially negates the need for new nets while contributing to
the circular economy through repurposing of fishing gear.
Standard trawls are typically constructed with 80 mm top sheets. Thomas previously tested 160 mm
and was pleased with the results. BIM assisted him in taking this a step further and set up a trial
which compared the performance 300 mm with 160 mm mesh top sheets. Assisted by Matthew
McHugh and Martin Oliver from BIM, a total of fourteen hauls were conducted on board the MFV
Cisemair with skipper David Reid in the Western Irish Sea in June 2024.
Nephrops catches were up 38% while catches of undersize whiting were down by 39% in the trawl
with the 300 mm mesh top sheet. The twine surface area was reduced by 8%. While it was not
possible to assess fuel consumption during the trial, Niall Connolly also fitted 300 mm top sheets and
reported a fuel saving of around 10% compared with 80 mm top sheets over a number of trips
targeting Nephrops onboard the MFV Mellifont with skipper Robert Dawe.
The increased Nephrops catch is a surprising result and may be due to improved ground contact of
the trawl associated with increased water flow. We plan to do more testing at sea and possibly in
the flume tank next year to confirm and improve knowledge around this result.
The reduction in undersize whiting is also an important result. BIM has conducted extensive research
on reducing whiting in the Irish Sea Nephrops fishery due to poor stock status and requirements to
improve whiting selectivity. Measures such as the Swedish grid and increased codend mesh size
have been shown to help in this regard but are also associated with losses in targeted Nephrops.
Also, it is not clear how well small whiting survive the process of escaping through diamond mesh
codends which raises questions over the efficacy of such a measure in boosting stock conservation.
Incorporating 300 mm mesh panels in the top sheet allows whiting to escape early in the capture
process through meshes which are much larger than their body size likely resulting in excellent
survival of escapees.
Increased Nephrops catches and reductions in fuel use can lead to
improvements in profitability while reducing carbon emissions as part of the energy transition. All in
all, enlarged top sheets hit the sweet spot of gear technology research with major potential to become a management measure supporting the sustainable development of the Irish Nephrops
fishery.
Thomas Whelahan and crew deserve credit for driving forward the development of enlarged top
sheets, as do Niall Connolly and crew, and Pepe Trawls Ltd for taking the initiative and doing their
own gear research.
This work is funded by the Irish Government and part-financed by the European
Union through the EMFAF Operational Programme 2021 – 2027. A full trial report is available at
www.bim.ie/publications/fisheries
I hope that information is used correctly. When introducing the square mesh panel the fishermen were asked about the best position for it. A few of us in skye working small gear found that the best place was on the crown this information was totally ignored and we were forced to put it in the wrong place. A lot of time and effort wasted for no reward.