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Evaluation of mesh measurement methodologies for fisheries inspection and research


The overall objective of the CA was to evaluate the present mesh measurement procedures for fisheries inspection and for research as used in the EU, to identify the problems related to these measurements and to define the requirements for a mesh gauge suitable for both inspection and scientific purposes.
Most of the participants agreed that the present EU legislation for mesh size measurement is not sufficiently precise and allows for variation in both the construction of the official wedge gauge and the operational procedures. This may lead to different results due to the use of mesh gauges that differ or to human influences when performing the measurement.

This does not mean that all inspection agencies reject the present EU measurement technique. A number like the simplicity of the EU wedge gauge and oppose drastic change. The others think that in the present situation it is not possible to make objective measurements. The majority of the participants are of the opinion that the essential requirements for reliable mesh measurements cannot be fulfilled by one of the existing instruments and recommend the development of a new mesh gauge.

The hearings organised in each country demonstrated that the industry's view on the problem runs remarkably parallel with that of the inspectors and scientists. The problems seem to be related to the targeted fish species and the fishing methods used.

The netting manufacturers and netmakers are in a particularly difficult position. Some groups of fishermen request netting with a mesh size as close as possible to the legal minimum to fish legally with minimal losses of marketable fish. Both the changes in mesh size due to use and variability in the results of mesh size measurement make this difficult to accomplish. In this respect, the introduction of quality standards for netting materials would be a major step forward.

There was a broad agreement between most inspectors, scientists, fishermen and the netting industry on the following points about the wedge gauge:

.the description in the EU regulations of the wedge gauge allows for differences in the construction of the instrument
.the EU wedge gauge does not allow an objective measurement due to the use of hand force
.skippers rarely contest the outcome of the measurement by hand as measurement with a weight mostly yields lower average mesh sizes
.most Courts in the EU member countries do not accept mesh measurements made with the use of a dynamometer
.some shapes of weight are claimed to be impractical and unsafe when boarding vessels.

The inspectors made the following comments on the measuring procedure:

.the procedure is too complex and time consuming
.it is not clear whether fishermen are allowed to clean the nets before inspection
.the selection of 20 successive meshes in large mesh cod-ends can be difficult
.the position of the mesh gauge relative to the knots should be specified
.the position on the gauge to read the mesh size should be specified
.the procedures for most EU waters and the Baltic Sea area are slightly different and should be uniform.

In general scientists use the ICES mesh gauge. Due to the fixed measurement force this instrument is much less susceptible to human influences. The measuring force is determined by a spring, a principle that is generally not accepted by Courts. The instrument needs regular calibration to ensure that the correct force is used. This can be regarded as a drawback but is also a guarantee of a consistent mesh measurement procedure. The ICES gauge needs more maintenance and the instrument is known to be liable to wear. The instrument is regarded as being too fragile for inspection purposes. There is a lack of uniformity in the measuring procedures used in research and there is a need to define the spring forces appropriate to different twine sizes.

The ICES gauge gives lower average mesh openings than the wedge gauge (either by hand force or 5 kg weight). This should be taken into account when defining minimum mesh sizes based on selectivity research in which the ICES gauge has been used.

Although the report does not exclude the use of different gauges to be preferred and used by enforcement agencies and scientists, the majority of the partners was of the opinion that the use of two instruments to determine the same measure was illogical and inefficient.

The industry strongly criticised the mesh measuring procedures used for inspection, in particular:

.that the measurement is not objective, due to the use of hand force. It leads to inconsistency between individual inspectors and between fisheries inspectorates
.the 5 kg weight is too small to stretch the mesh completely in thick twine netting and could be increased
.that mesh size is not measured in the same way at all stages from netting manufacturer to inspector
.that the imprecision of the mesh gauge be taken into account by inspectors.

The participants in the Concerted Action rejected the argument for a tolerance to be applied to the average measured mesh size. It was feared that if this had been allowed fishermen would work towards the smallest possible mesh size. The idea of certificated netting or cod-ends was regarded as unworkable since it obscures responsibility for undersized netting.

The wedge gauge, and to a lesser extent the ICES gauge, are not always suitable instruments to measure the mesh sizes of some types of netting. Differences in construction and material properties, such as elasticity, stiffness and friction, can lead to different readings being obtained from different netting with the same mesh size.

Determination of the mesh size of fine netting was not discussed in detail since the gears using this netting now fall under Commission Regulation (EC) No 2550/97 of 16 December 1997. The participants regretted that the instrument described in the new Regulation has the same shortcomings as the EU wedge gauge. The description allows for too much variation in the construction of the instrument and it was felt that a better-defined gauge for passive gears is needed. Since the instrument should be operated by hand force only, the objectivity of the measurement may again be questioned. Furthermore, it was stressed that the introduction of any new measuring instrument or procedure should be preceded by careful testing.

Thick twine netting causes problems for mesh measurement: positioning of the gauge relative to the knots; reading the mesh size off the scale; handling the cod-end to make the measurements; selecting 20 consecutive meshes.

In small mesh cod-ends appending the weight can be a problem.

Some types of netting can reduce the selectivity of the cod-end although the mesh size may be legal. The use of special netting to reduce selectivity can best be discouraged by legislation to ban the use of such material. The use of special netting or devices to improve selectivity however, may require instructions on how to measure the mesh size, e.g. Swedish exit windows.

Other existing ways of measuring mesh sizes were considered but none was found to have major advantages over the wedge gauge or ICES gauge.

The one-dimensional nature of current mesh measurements does not penalise the use of netting designed to reduce selectivity. A two-dimensional measurement method is needed but the problems identified by the participants in developing such a device, e.g. a cone gauge, suggest that it will be a long-term task.

The participants agreed on the requirements for a model mesh gauge. It was recognised that none of the existing mesh gauges met these requirements. Hence, it was recommended that such an instrument be developed, preferably in the framework of an EU research programme.

Considering that the development, testing and implementation of a new instrument may take a long time, a number of improvements to the existing EU gauge were proposed, aimed at further standardisation of the instrument and the operating procedure.


Hearings were organised in all 13 participating countries to inform the fishing industry (fishermen and netmakers) about the project and to learn the industry's view about the problem. A list with venues and dates is attached.
As an introduction to the hearings articles on the project were published in most national fisheries journals. Some journals also reported on the hearings proper.
The project was presented in Fishing News International (March 1997).
A small press conference was held after the first project meeting in Sweden (January 1997).
The progress of the project was presented to the ICES Working Group on Fishing Technology and Fish Behaviour (FTFB) at its 1997 and 1998 meetings (Hamburg, Germany, 14-17 April 1997; La Coruna, Spain, 20-23 April 1998).
As a result of the Concerted Action ICES was asked to review the procedure for measuring mesh sizes with the ICES gauge at the 1998 Annual Science Conference (Cascais, Portugal, 16-19 September 1998). The request was accepted and a recommendation on this topic was made to Working Group on Fishing Technology and Fish Behaviour.
The project and its outcome were presented to the Working Group involved in the drafting of European standards on fishing nets (CEN - TC 248/ WG 3: Fishing nets) at its meetings in Brussels on 3 February 1998 and in Paris on 13 October 1998. The results of the project will be taken into account when drafting a standard on methods for the determination of mesh size.
After approval of the final report by the Commission the national partners will disseminate the results to the fishing industry in their respective countries. The results will also be communicated to the international fishing press.
To fulfil this objective a detailed review and comparison was made of present mesh measurement methodologies in and outside the EU, involving problems arising from the use of specific netting. Essential in the evaluation process was the organisation in each participating country of hearings involving fishermen and netmakers to define the problems encountered in the industry. Based on all information gained, the requirements for a model mesh gauge were described and recommendations for future work, i.e. the development of a new gauge gauge to be used by both fisheries inspectors and scientists in the EU, were made.

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