Does the monofilament nylon gillnets catch double more fishes than conventional multifilament gillnets in Danube delta: myth or reality

The monofilament gillnets are prohibited by law for fishing in Romania. There is an untested myth among Romanian fishery stakeholders and folks that monofilament nylon gillnets have double times fishing catch than conventional multifilament gillnets. This myth provoked controversial debated between the fishermen, administrators and conservationist for the regulation purpose. To answer this dilemma in year 2014, fish fauna from Danube delta lakes was sampled with two type of research Nordic gillnets, multifilament (MF) gillnets versus monofilament (MO) gillnets (European Standard CEN EN14757:2015(E). Both types of fishing gears were randomly assembled from 12 mesh panels with mesh sizes of 5, 6.25, 8, 10, 12.5, 15.5, 19.5, 24, 29, 35, 43, 55 mm knot to knot. To compare fishing efficiency of two types of gillnet, 4 largest lakes inside of the Danube delta, respectively Furtuna, Merhei, Isac and Roșu lakes were sampled. The relative abundance and biomass, standardized as Catch per Unit of Fishing Effort (CPUE), expressed as number or weight per 100 m2 of gillnets per night fishing, were estimated. Accordingly with sampling test, MO gillnets caught in average more than two times more fish in abundance and/or biomass than MF gillnets. The figures are different by species, season and lake. Considering this proven of evidence, it is a policy and societal choice for future MO gillnets fishing regulation. Management regulation of MO gillnets, should consider both, socio-economic benefits and environmental impacts for sustainable use of fish resources. Simply management approach of permitting double efficient MO gillnets for more effectiveness fishing, require at least half decrease of fishing effort or capacities. That means half cutting off of the number of the fishermen permits or fishing time or number of gears or a combination of these measures, in order to maintain at least actual fishing pressure and avoid overfishing risk. Since the result refer to research sampling gillnets, future fishing selectivity study of the commercial MO, MF as well as multi-monofilament gillnets (MM) is needs