A new survey is set to challenge the image of Thurso's now-famous seal colony as salmon-guzzling freeloaders.

The local woman co-ordinating the research has so far had no reported sightings of the common seals eating salmon in the month since the watch started.

Jenny Paterson believes that the seals, which have been as many as the high 20s, are taking temporary refuge from their normal home at nearby Scrabster Beach

Since the start of their frequent sorties to river islands near the town's main bridge last October, the colony has proved something of a crowd-puller.

But they are blamed by river managers for feasting on salmon returning to the river.

Abortive efforts to deter them have ranged from erecting fences around the islands and installing scarecrows while plans to float an inflatable killer whale at the mouth of the river were abandoned.

River owner and local MP John Thurso last month made clear he would not countenance river superintendent Eddie Mcarthy exercising his legal right to shoot the seals.

Efforts to get logs of the seals' activities while on the river were initiated by International Animal Rescue, which is planning a £2 million seal sanctuary at John O'Groats.

A handful of volunteers, led by Mrs Paterson, have given up their free time over the past month counting the seals and monitoring what they do when they arrive before and after high tides.

The watch had revealed a reduction in the number of the colony, which is believed down to the onset of the breeding season. Over the past week, the number has dwindled to a handful.

Mrs Paterson, a member of a local marine life rescue group, believes the seals on the river were previously based on Scrabster Beach before being scared away by the major pier works underway at the port.

Mr McCarthy is astounded by the lack of any sightings of seals taking salmon. While he has not seen one of the seals take a salmon, he has been been given eight or nine sightings from members of the public while an angler has reported seeing seal marks on a salmon which he caught.

He was also sceptical about the theory that the seals were previously based at Scrabster.

Mr McCarthy said all the seals he has seen at Scrabster have been grey, rather than the common variety which have frequented the river.