Het Omega project

A new hi-tech method for checking the mesh size of fishing nets

The bigger the holes in a fishing net, the more young fish will be able to escape, grow bigger and breed. So to protect young fish, managers set minimum mesh sizes for fishers’ nets.

Making sure that nets comply with government recommendations is the difficult job of fisheries inspectors. But it is not just fisheries inspectors who check mesh. Scientists also need to check the size of the mesh they use for surveys to make sure it is the standard size. Both scientists and fisheries inspectors use their own type of measuring gauge to check mesh size and both groups have been pushing for many years for a new gauge.

The wedge mesh gauge

The first known rules on minimum mesh sizes for fishing nets were set in 1291 by Philip IV (The Fair) of France . He stated that the mesh opening should not be smaller than the size of a “gros tournois d’argent”, a common coin of those days. Remarkably this simple principle of measurement is still applied in the flat wedge mesh gauge used today by fisheries inspectors. To measure the mesh opening, the wedge is pushed into a mesh until stopped by the resistance of the yarns.

The major drawback is that the measurement depends on the force applied and so is not free of human influence. This can have serious consequences: due to the lack of objectivity of the method, courts have declined to prosecute in several cases when the evidence was obtained with the wedge gauge.

The ICES mesh gauge

Scientists use a different gauge. The ICES mesh gauge was first developed and manufactured under the guidance of the International Council for the Exploration of the Sea in 1962.

The old ICES mesh gauge

When used in fishing gear selectivity experiments the measurements from the ICES mesh gauge are the basis for scientific advice on minimum mesh sizes. The ICES gauge exerts a fixed longitudinal measuring force on the mesh. The recommended measuring force is 4 kgf

When the ICES gauge is correctly used, the measurements are free of human influence. But the major drawback is that the measuring force is controlled by the compression of a spring, the characteristics of which may change over time. This makes the instrument unsuitable for the enforcement of mesh regulations.

Developing a new gauge

Over the last decade the merits of these mesh measurement methods have been questioned frequently. Both the ICES mesh gauge and the wedge gauge are no longer regarded as suitable for mesh measurement on modern thick twine netting.

Both types of instrument have been used in parallel since the 1960s but give different results when used on the same netting.

The ICES gauge yields lower values of mesh opening than the wedge gauge. This has an adverse effect on the selectivity of commercial towed fishing gears as the mesh sizes in commercial use are, as a result, smaller than those recommended by the scientists.

This has led to a demand for standardisation of the mesh measurement technique by fisheries inspectors, scientists, and the industry (netting manufacturers and net makers as well as fishers).

The new “state-of-the-art” OMEGA mesh gauge

To deal with this problem, ICES set up a Study Group on Mesh Measurement Methodology (SGMESH) in 1999. The Study Group presented its final report in 2003 which included the recommendation that everyone should use the same system of mesh measurement: a longitudinal force of either 40 or 100 N – depending on whether the mesh opening is <55 mm or ≥55 mm.

Further recommendations concerned the number of meshes to be measured and the measurement procedure. Since the recommended forces could not be exerted by the ICES gauge, it was apparent that a new instrument was required.

The task of developing a new gauge was undertaken in the EU-sponsored research and demonstration project OMEGA: “Developing and Testing of an Objective Mesh Gauge” (QoL, Fifth Framework Programme). The main aim was to build and test a new, objective mesh gauge, suitable as a standard instrument for all user groups.

The partners in the project were fisheries inspection services and fisheries research institutes from Belgium , France , Germany , Italy , the Netherlands ,Spain, and the United Kingdom.

The new gauge was built as a joint venture by two instrument makers, applying the latest technical ideas. Fisheries inspection services and research institutes from the other EU and ICES member countries, as well as Turkey and NAFO, netting manufacturers, and fishers were also involved in testing and evaluating the OMEGA mesh gauge. Extensive trials were carried out under both laboratory conditions and at sea.

How does the OMEGA Gauge work?

The OMEGA mesh gauge is an electrically driven instrument that applies a pre-set longitudinal force to the mesh to be measured. Once this force is reached, the exact opening of the gauge is measured automatically.

Mesh opening and measuring force are shown on a digital display. A series of measurements can be performed and the readings are stored in an integral memory. At the end of the operation the number of measurements made and the average mesh size are shown.

Stored data can be transferred to a computer via an infrared link. Calibration can be carried out routinely by means of a test plate with a range of fixed opening lengths and a set of weights.

The OMEGA gauge is not only suitable for diamond, square, and 90° turned meshes in active fishing gears but also for the fine twine meshes of passive gears. The extensive trials by scientists, fisheries inspectors, and netting manufacturers revealed the need for a slight modification of the measuring forces advised by SGMESH. Depending on the mesh size, forces of 20, 50, or 125 N are applied to the netting of active gears.  A single measuring force of 10 N is used for passive gears.

The OMEGA Gauge meets with success

The ICES-FAO Working Group on Fishing Technology and Fish Behaviour (WGFTFB) ( Rome , April 2005) considered that the OMEGA gauge meets the essential requirements set out by SGMESH and therefore recommended the OMEGA gauge as the new standard gauge to replace the ICES gauge. This recommendation was confirmed by the Fisheries Technology Committee (FTC) at the 2005 Annual Science Conference and subsequently adopted by the Council.

In the near future, the European Commission will consider the use of the OMEGA gauge for fisheries inspection. The European Committee of Netting Manufacturers (EUROCORD) also recommended the use of the OMEGA gauge during the production of sheet netting and urged the European Commission to review the Commission Regulation on mesh measurement and adopt the OMEGA gauge.

Use of the OMEGA gauge, as a standard for inspection, science, and industry, will lead to improved enforcement of the regulations on mesh sizes and the use by fishers of the exact mesh sizes recommended by scientists. This will contribute to achieving sustainable exploitation of the fish stocks. More objective monitoring of mesh sizes should restore confidence in the value of technical measures. It should also eliminate the present legal uncertainty which exists in the fisheries of some countries.

The OMEGA mesh gauge.

The OMEGA mesh gauge became available commercially in the spring of 2005. It is a “state-of-the-art” device and already in demand. More information on the new gauge is available by downloading a recent ICES Cooperative Research Report.


Ronald Fonteyne
OMEGA Project Coordinator
Agricultural Research Centre – Sea Fisheries Department