Monitoring of zebra mussels in the Shannon-Boyle navigation, other

Abstract

The zebra mussel (Dreissena polymorpha) population has been closely monitored in Ireland following its discovery in 1997. The species has spread from lower Lough Derg, where it was first introduced, to most of the navigable areas of the Shannon and other interconnected navigable waters. This study took place in the summers of 2000 and 2001 and investigated the relative abundance and biomass of zebra mussels found in the main navigations of the Shannon and elsewhere in rivers, canals and lakes where colonisation was likely. During 2000 zebra mussels were found for the first time in Carnadoe, Kilglas and Grange Loughs on the River Shannon. In 2001, they were discovered on the Ballinasloe Navigation at Poulboy Lough and in Ballinasloe Harbour. For the first time outside of the Shannon-Boyle navigation, established populations were discovered in Garadice Lough on the Shannon-Erne Waterway and in Ringsend Basin and Tullamore Harbour on the Grand Canal. Zebra mussels continue to have their greatest densities in lakes and large reservoirs of the Shannon-Boyle navigation. A maximum biomass of 4.1kg per sq.m was recorded in Lough Key. No zebra mussel larvae or their attached stages were found in the larger lakes outside of the Shannon-Boyle and Erne Navigations. Larvae were found however, in Tullamore Harbour for the first time. In separate studies approximately two hundred adults were found in Lough Bo, Co. Sligo and less than ten specimens were found in Lough Gill, Co. Sligo. The only living population of native freshwater mussels (Anodonta spp.) presently known in the lake regions of the Shannon is in the Carnadoe Cut, between Carnadoe Lough and Kilglas Lough. This population of Anodonta spp. is fouled with zebra mussels. Freshwater mussels were also found in Garadice Lough and Assaroe Reservoir. These were also fouled with zebra mussels.