AN ASSESSMENT OF FISH PREDATION ON THE ZEBRA MUSSEL, DREISSENA POLYMORPHA (PALLAS 1771) AFTER RECENT COLONISATION OF TWO MANAGED BROWN TROUT LAKE FISHERIES IN IRELAND

Abstract

The zebra mussel (Dreissena polymorpha, Pallas 1771) invaded Lough Sheelin in the midlands of Ireland in 2001, providing a novel potential food resource for the resident fish species. This paper assesses fish predation on the mussel after the recent colonisation of the lake (with supplementary data from Lough Arrow). In addition, implications for the resident fish community are considered. Roach (Rutilus rutilus L.), and roach—bream hybrids (R. rutilus × Abramis brama L.) were found to consume zebra mussels in all sampling seasons. For other fish species (European perch [Perca fluviatilis L.], northern pike [Esox lucius L.] and the brown trout [Salmo trutta L.]) the occurrence of zebra mussels in the diet was low, in addition to being seasonal, and possibly consumed as incidental by-catch in some cases. The incorporation of mussels into the diet represents the most important change to the feeding habits of cyprinids. Adult roach populations have not increased despite feeding on zebra mussels and appear to be the most negatively impacted fish taxa since the establishment of the mussel in the lake. Brown trout and perch may be advantaged in the long-term, most likely due to reductions in chlorophyll a, habitat changes and altered food resources. The extent of fish predation on zebra mussels does not appear to be sufficient to suppress the mussel population in the lake.