Scientists are "fed up apologising" and want to be heard. That was the message from Dr Peter Smith, the main organiser of an international conference on fishfarming and the environment which was held in Galway late last week.
It was held to celebrate 20 years of research by NUI Galway's Fish Disease Group, and the organisers calculatedly chose a well-worn but still very controversial theme. The aim was to present enough scientific evidence to make the case for the "insignificant impact" of the fish-farming industry on Ireland's marine and freshwater environment.
What really sparked it off, according to Dr Smith, was a recent ESRI report which referred to the excessive use of chemicals in the industry here. "There is plenty of scientific research available to show that this just isn't true," Dr Smith said.
"I just want to see that data out there acknowledged. It would appear that the results of serious scientific work have been lost in the media debate on aquaculture."
As he suggested in his own presentation on the fate of therapeutic chemicals, the pig and poultry farming industries use far greater concentrations of many agents, and yet with far less regulation.
In fish-farming, the largest body of information available concerns the environmental fate of the anti-microbial agent, oxytetracycline.
A study of its use at over 17 farm sites in Norway, Finland, the US and Ireland, found the drug can be traced only in low concentrations, and very near the cages.
Increases in resistant bacteria resulting from the use of the drug were moderate, and were also confined to the immediate farm area and were of limited duration, he said. "Simple mathematical modelling demonstrates that, as it is used in fish-farming, oxytetracycline cannot reach biologically significant concentrations in the water."
Studies of the anti-lice drug, ivermectin, had also demonstrated that accumulation in under-farm sediments was also extremely low, he said.
In a study at an Irish farm, the mean concentration was five parts per billion. Studies of the fauna in these sediments revealed no significant impact on populations of pollychaete worms, a group thought to be extremely sensitive to this agent.
Ultimately, the use of chemicals was a "failure of management", he said. Site fallowing, using three-site rotation, has been acknowledged in recent years as the best way of ensuring fish were reared disease-free. The problem sites appear to be where there is heavy feed accumulation, poor currents, low oxygen levels, and no worms to do nature's work on sediments.
Also speaking on a similar theme, Dr Brendan O'Connor, of Aqua-Fact International Services in Galway, said a recent review of water chemistry data from Kilkieran Bay, Galway, which included information collected before salmon-farming began there, showed there was no statistically significant increase in pollution due to organic wastes. Many surveys of Irish salmon-production sites also indicated that impact of solid wastes, like uneaten food pellets, on the sea floor was confined to within 10 metres of the edge of the cage.
Dr Mark J. Costello, of Ecological Consultancy Services Ltd, said there was insignificant pollution of rivers due to freshwater fishfarm effluents.
In 1993, a study funded by the Department of the Environment and the Environmental Protection Agency under the EU STRIDE programme involved collecting water samples from half of the State's rainbow trout and salmon farms in freshwater areas, and study of other data.
He said pollutant loads varied seasonally with fish-feeding activity, and with the amount of fish present.
Examination of water chemistry and riverbed invertebrates downstream from the site discharges indicated 9 per cent of farms were having undesirable impacts on river quality within 200 metres of their discharge outfalls.
However, even these farms could not be considered to be polluting rivers to the extent that natural fish, invertebrate and wildlife populations could be affected, he said.
Speakers from Ireland, Norway and Scotland delivered presentations on monitoring strategies, and on the application of new technology to fish-farms.
"We cannot expect that the world's food production can be increased without any environmental impact", Dr Torbjorn Asgard of the Institute of Aquaculture Research in Sunndalsora, Norway, said, talking about new developments to contain farm waste. "But if we should avoid a future collapse in food production, it is important to develop our activities in a way which is resource-efficient and minimises environmental impact."
