Many technical measures aimed at the conservation and recovery of fish stocks are based on the implementation of minimum mesh sizes to guarantee a certain level of fishing gear selectivity. At present, different methods are used to measure mesh opening, according to whether the measurement serves fisheries inspection, fisheries research or the manufacturing of netting for fishing nets. At the very least, this causes confusion but can also have more serious consequences such as the criminalization of well intentioned fishermen or the setting of inappropriate mesh size regulations. For example, the measurements made by fishery inspectors using the wedge gauge are generally larger than those made by scientists using the ICES gauge. As a result the cod-ends used by fishermen to satisfy the fishery inspectors will have a selectivity lower than that anticipated by the scientists who provided the advice that informed the relevant legislation. In 1999, owing to the wider range of twines and netting materials used by the fishing industry, ICES established the Study Group on Mesh Measurement Methodology (SGMESH) to refine mesh measurement procedures. At the same time the different stakeholders agreed that there was a need to consider the adoption of a standard mesh measurement method. A major step in the standardization of mesh measurement methodologies was the development of a new standard mesh gauge (2002-2005). In October 2005, it was adopted by ICES as the new standard for mesh measurements and in June 2006 the Northwest Atlantic Fisheries Organization (NAFO) recommended its use for scientific purposes. This review paper critically examines the different mesh measurement methodologies and their related problems, and introduces and describes a new objective mesh gauge (OMEGA) to replace the former less satisfactory gauges. Its adoption will result in researchers, fisheries inspectors and the netting industry using one standard gauge and one set of standard protocols to achieve consistent mesh-size measurements.
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