Asian clam a serious threat to aquatic life in Lough Derg, warns expert

THE invasive Asian clam has just been discovered in Lough Derg where it is likely to have serious impact on the biology of the lake, an expert has warned.

Dr Dan Minchin, a marine biologist with the Lough Derg Science Group in Ballina, Co Tipperary, said the main impact of the clam (Corbicula fluminea) would be on the environment of Derg, the Shannon’s largest lake.

The lake is targeted by Dublin City Council as the source of an alternative water supply for the capital city. Dr Minchin warned the existence of the clam could further pollute the waters of the lake.

He discovered the invasive clam in the lake earlier this month while undertaking survey work.

He said the population of the Asian clam can grow rapidly.

“It can form densities of almost 10,000 per square metre. These kind of densities would have notable consequences for the lough,” he said.

Dr Minchin said the sheer volumes of clams on the bed of the lake, a world renowned angling resource, may deprive fish and other water life of vital nutrients.

“Such is its reproductive capability that it is likely to have serious impacts on the biology of Lough Derg as it can produce many young,” he said.

“Its impact on the food for fishes in this important angling lake is unquantified at present,” said Dr Minchin.

He said the invasive bi-valve, which can grow to three centimetres in diameter, was found in the lower Barrow and Nore last year. Its downstream spread to Derg was inevitable but Dr Minchin expressed surprise at how short a time it had taken it to appear in the lake.

He had not expected it to appear for at least four more years. Dr Minchin said he was concerned huge volumes of the clam on the bottom of the lake could use up scarce oxygen in spells of warm weather, with potential lethal consequences for other aquatic life.

The clam could also have negative impact on the tributary rivers of the lake where fish such as trout and salmon spawn.

“It seems to reach its highest densities in rivers, so you have a double whammy,” he said.

The Asian clam’s arrival in Ireland was first discovered in the River Barrow early last year. At that time Dr Joe Caffrey of the Central Fisheries Board said it posed a threat to salmon, trout and other native species such as the freshwater pearl mussel.