A study of fishing nets with different mesh sizes aimed at reducing cod by-catch has concluded that too much of other species is lost at the same time to justify their use.
The trial, commissioned by Marine Scotland Science in partnership with the Shetland Fisherman’s Association, was undertaken by the Shetland fishing boat Resilient last summer.
It involved trawling with larger net mesh sizes, replacing the standard 120mm mesh nets with of mesh of 300mm and 600mm, to assess the extent to which cod by-catches in the Shetland mixed whitefish fishery would be reduced.
While the nets did reduce the amount of cod caught by 49 per cent, there was also a reduction in the amount of other valuable species, leading Shetland Fisherman’s Association chief executive Hansen Black to describe the nets as “unsuitable for Shetland”.
Mr Black said: “The trials were something that we put forward due to concerns that the so called Orkney nets had been incorporated in the EU-Norway agreement and there seemed to be a growing move towards boats fishing with cod avoidance nets.
“We were concerned that these … nets would have a big impact on cod we catch as part of the mixed fishery.”
Shetland’s fishermen rely on catching a selection of species to be economically viable. This includes some cod.
Mr Black said: “The boats that fish in and around Shetland catch cod, haddock, saithe, megrim, monkfish … so it’s the whole package, it’s not a fleet that relies on haddock.”
The trial resulted in catches with slightly more haddock, however there were “significant losses”
in catches of ling, megrim and monkfish, with monkfish being particularly significant as Shetland’s most valuable catch.
The trials of nets with 300mm resulted in a 49 per cent reduction in the amount of cod caught, but also 80 per cent fewer megrim, 50 per cent less monkfish, 36 per cent fewer ling and 28 per cent fewer hake.
Mr Black said: “For twin rigged boats, the losses would outweigh any gains to be made. What it showed is that for Shetland’s mixed fishery boats the net [is] unsuitable.”
The report recommended that due to the economic importance of these species for Shetland “further research should be directed towards the development of gears that reduce catches of cod but retain species such as monkfish, megrim, ling, saithe and hake and which, presumably, would be more attractive economically”.
A Scottish government spokesman said: “I congratulate the Shetland fishermen for taking forward this research which has produced very promising results for the industry Scotland-wide.
“Scotland continues to be at the forefront of developing increased gear selectivity and this project will enhance our knowledge in this field. This initiative has helped bridge the gap between fisheries scientists and the catching sector. Both undoubtedly have vital knowledge to share with the other for mutual benefit.”