HUGE numbers of fish are being eaten by seals as they attempt to navigate the Tees Barrage, a pilot study has revealed.

The results of the three- week study, designed to test the effectiveness of a so-called "fish pass" at the barrage, have been described as alarming by British Waterways, which owns the barrage.

But environmental watchdog the Environment Agency said they were just a snapshot and may not be representative.

The pilot study was suggested by the agency and carried out by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) on British Waterways' behalf.

It found that 49 per cent of a sample of salmon and sea trout in the Tees Estuary area had been eaten by seals.

The fish in the survey had been electronically tagged so their movement over a 21 day period could be monitored as they swam upstream towards inland waters.

Alan Slater, river manager for British Waterways, said "The conditions at the time of the study were favourable for the fish to pass the barrage, so this makes the results even more alarming."

Some anglers have claimed the fish pass is too narrow and effectively "bottles up" migratory fish, making them easy prey for seals.

However, Mr Slater said there was no proof of this and that there were other methods for the fish to swim past the barrage, including a canoe slalom and gates which they could leap over.

Richard Jenkins, ecological appraisal team leader for the Environment Agency, said: "This is a huge number of fish to be lost.

"But we must take into account that these results are a snapshot and may not represent the full picture.

"What the findings show is the need for a more detailed study, to include an assessment of the seals' predatory habits, covering a range of environmental conditions, so we can make any decisions about the fish pass on the basis of sound, representative information."

The fish pass, which is intended to ease fish passage through the barrage, was built in 1994 after being given provisional approval.

However, due to the ownership of the barrage having changed hands several times over that period, final approval for the structure has never been sought.

The barrage itself, which opened in the early 1990s, is designed to protect the river from pollution discharged into the Tees estuary and is said to have been responsible for an increase in both water quality and wildlife.