Porpoises living in the Irish Sea carry increased levels of radiocaesium which must be linked to Sellafield, according to a joint research project carried out by Irish and British scientists.
There is no evidence, however, to suggest the increased levels have a detrimental effect on the health of the porpoises, say the scientists from University College Cork, the Radiological Protection Institute of Ireland and the Sea Mammal Research Unit in Cam bridge.
The scientific team, led by Dr Simon Berrow and Ms Stephanie Long of the RPII, based their research on an analysis of muscle samples collected from 25 harbour porpoises, Phocoena phocoena, which had been stranded on Irish and British coasts, or by-caught in fishing nets.
The sex and weight of the animal was recorded when possible, and about 200 grammes of muscle tissue were examined for gammaemitting radionuclides by high-resolution spectometry.
The analysis focuses on concentrations of the naturally-occurring radionuclide, potassium-40, and the artificial radionuclide, radiocaesium (137 C).
The potassium-40 concentrations were consistently higher than those of radiocaesium throughout the range. The mean radiocaesium concentrations were much greater, however, among the samples taken from porpoises in the Irish Sea than among those found on the Atlantic, Celtic Sea and North Sea.
There was no difference in radioactivity concentrations between the sexes.
Dr Berrow, who is based with the British Antarctic Survey, said there was little doubt that the source was Sellafield. But though significant, the effect of radiocaesium on the health of the animals could not be determined, he said. "It certainly can't be good for them."
The study was funded by the Heritage Council as part of a contract on the health status of cetaceans in Irish waters, and the full results have been published in the 1998 Elsevier Science Ltd's Marine Pollution Bulletin, volume 36. A second study published recently by Dr Berrow, along with Ms Maria O'Neill and Ms Deirdre Brogan, in the Proceedings of the Royal Irish Academy, found the by-catch of marine mammals in mackerel and herring trawl nets was not significant.
This study was carried out on commercial trawlers fishing for herring in the Celtic Sea during the 1994-95 season, and Dr Berrow compliments the skippers concerned on their willingness to co-operate. During the study, 85 days were spent at sea, with 78 tows monitored, which was about 7 per cent of the total effort of the fishery. Overall, 1,270 tonnes of fish were observed being caught, of which 1,214 tonnes were landed and the rest discarded.
The non-target fish species recorded was most frequently whiting, while mackerel and horse-mackerel were also found in nets.
Four grey seals, Halichoerus grypus, were caught during the study at a rate of one per 317.5 tonnes of fish or 0.05 seals per tow. This catch rate extrapolates to around 60 seals caught in the fishery - not thought to have a significant impact on the Irish seal population.
Dr Berrow - author of a previous study on the effect of gillnets in the Celtic Sea which found that there was a 6 per cent take of porpoises - enters a caveat. Scientists sought initial permission to board the largest trawlers in the Irish fleet, working from Killybegs, Co Donegal. But this was not granted.
"We cannot give definitive results without looking at the effect of the largest, most intensively fishing, vessels," he says.
Mackerel and herring (pelagic) fisheries account for 83 per cent of the total fish landed into Irish ports, with mackerel, horse-mackerel and herring constituting 97 per cent of this.
Meanwhile, the initial trials to find alternatives to the drift-net for tuna have proved somewhat disappointing. Tuna skippers in the south-west, who have unsuccessfully opposed the outright ban imposed by the European Com mission from 2002, are understandably frustrated.
Dr Berrow has some sympathy for them, as he believes that drift-nets do have a role to play, but is also concerned about the effect of the alternative method - pair trawling - on cetaceans.
He hopes the by-catches will be recorded by the skippers and scientists involved in the BIM trials, with this in mind.
