Clam find prompts call for more Shannon monitoring

THE discovery of one of the world’s most invasive clam species in Lough Derg has sparked a call from a local marine biologist for increased monitoring of the River Shannon.
Dr Dan Minchin of the Lough Derg Science Group discovered the presence of the Asian clam and believes more sampling of rivers and lakes is needed to monitor the impact and spread of such species.
The Asian clam (corbicula fluminea) is regarded as one of the most invasive species found in freshwater habitats and was first discovered in Ireland by biologist Dr Pascal Sweeney in the lower reaches of the River Barrow. Inland Fisheries Ireland research staff found dense populations in the Barrow, with almost 10,000 clams per square metre. It was also found in the Nore last year.
Able to grow to three centimetres in diameter, such is its reproductive capability that it could have a serious impact on the biology of Lough Derg.
A survey downstream of Rooskey conducted by Dr Minchin last year did not reveal any specimens. This survey extended to Lough Derg last July and covered most regions of the lake. It was only last week that young specimens were found in depths of over 20m in the lake.
Dr Minchin said the clam would not cause the levels of fouling that zebra mussels do by attaching to boat hulls. However, its shells can accumulate and block pipework. “The main impact will be on the environment. It filter feeds in the same way as zebra mussels and it has a foot like a cockle that can extract nutrients from sediments. Its impact on the food for fishes in this important angling lake is unquantified at present,” he said.
Dr Minchin, who first came across this clam in the Canal du Midi in the South of France and studied the species in North America, is concerned about the impact it could have on the lake. He explained that in periods of prolonged hot weather, the water on the surface of the lake separates from the cooler water below and over time, oxygen gradually gets used up.
“Clams need a lot of oxygen, so in May or June when a difference of up to 8Cº between the surface and lower water can prevail, the water near the bottom could lose oxygen and much of the life in this cold zone might die should there be a prolonged hot spell.
“It is very difficult to try and remove alien species once they arrive so the best solution is to try and prevent them from coming to Ireland in the first place. The Asian clam has been in Britain for about 12 years, having arrived from the European continent and species that Britain receives, we are likely to get at some future time. It is extremely important that all individuals or user groups that have any involvement with Lough Derg play their part in ensuring that this high-impacting Asian clam is not spread to other rivers or watercourses” he said.
This species is likely to be of concern regarding the management of the Water Framework Directive for the Shannon International River Basin District.
Dr Joe Caffrey, senior research officer with Inland Fisheries Ireland, is regarding this species as potentially dangerous.
“If we are to win the battle against invasive species, we must be biosecurity aware and actively stop the spread of these pernicious species. The Asian clam probably represents one of the most potentially damaging invasive species to reach our shores. It is imperative that every action to bring it under control is taken,” he noted.