An investigation into the effectiveness of mechanical dredging to remove Corbicula fluminea (Müller, 1774) from test plots in an Irish river system

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The invasive Asian clam Corbicula fluminea (Muller, 1774) has established a high density and self-sustaining population within the tidal reaches of the River Barrow, Ireland. A field trial was carried out to test the respective efficacy of three different mechanical dredge methods at reducing Corbicula clam numbers by estimating changes in abundance and biomass immediately following dredging. Quadrat samples were collected by SCUBA divers before and after dredging. A maximum pre-dredge density of 17,872 individuals/m 2 and a biomass of 43.94 kg/m 2 was recorded. Three sites which supported different population density and biomass levels within the tidal section of the River Barrow were subject to each of the dredge methods. A reduction of greater than 95% biomass and 95% density was achieved at the high density, high biomass site, while an 82% biomass and 65% density reduction was recorded at the low density, low biomass site. A 74% biomass and 92% density reduction was achieved at the high density, low biomass site. The methodology and results indicate that, while dredging can achieve a large reduction in Corbicula population numbers, further research is required before this can be considered as a management tool for control of Asian clams.