Mesh Size Measurement Revisited

In 1291 Philip IV the Fair, King of France, forbade “de

pescher avec engins de file de quoy la maille (n ait) la

moule d’un gros tournois d’argent” or, to fish with nets

with meshes smaller than the size of a silver coin of that

time (Hovart, 1985). This silver coin can be seen as a

predecessor of the present-day wedge gauge used to

check whether the meshes of fishing nets comply with

modern technical regulations. A mesh gauge developed by C. J. W. Westhoff under the auspices of the ICES Comparative Fishing Committee became the standard gauge for research activities in ICES countries in 1962 (ICES, 1962a) and became known as the ICES gauge (Figure 1). To make a measurement the ICES gauge exerts a fixed longitudinal measuring force on the mesh. The recommended measuring force is 4 kilogramforce (kgf). When the ICES gauge is correctly used, the measurements are free of human influence. Since its introduction the ICES gauge has been generally used in selectivity experiments, to provide scientific advice on minimum regulated mesh sizes. However, since 1962 a wide range of new twines and netting types have been adopted in the fishing industry. These modern twines vary significantly in thickness and stiffness, characteristics which affect both mesh size and selectivity. For fisheries inspection the legal mesh gauge is the much simpler wedge gauge (Figure 2). The wedge gauge is normally operated by hand force and this makes the measurements liable to human influences. Therefore, a weight or dynamometer is used to control the measuring force in case the measurements are contested. Because this procedure generally yields lower mesh openings than

the hand force, it is hardly ever requested by the fishermen.