Report of the Study Group on Mesh Measurements Methodology (SGMESH)

1) A variable force proportional to twine linear density would be preferred but there are practical difficulties with this approach, principally the accurate measurement of linear density or twine diameter at sea.2) It follows that two groups of netting are recommended to which two standard forces apply for:a) netting under 55 mm mesh size and b) netting of 55 mm or greater mesh size.3) A longitudinal force is preferred to a perpendicular force and this confirms the principle of mesh measurement used in the present ICES gauge.4) Analysis shows that a measurement force of 40 newton would be appropriate for the smaller, 100 newton for the larger mesh.5) A force of 40 newton can be exerted by the current ICES gauge but 100 newton is out with the range of this instrument. The group is aware that a new gauge is being developed with a capacity of 180 newton but this instrument will not be available until 2005. It is recommended that in the meantime for scientific work the ICES 4 kg gauge be used but the results should be converted to 100 newton equivalent using a conversion formula.6) In most cases the measurement of 40 meshes would be sufficient for a precision of 1 mm at 95% confidence limits. If this is not the case after 40 meshes then measurements should continue until such precision is attained.7) It was noted there is variance in all methods of mesh measurement studied and this is attributed mainly to the variability of material.