Bran, a nine month old grey seal, was the first of his kind in Europe to be fitted with the sophisticated equipment.

But less than three weeks after the £5,000 device was fitted for the pioneering monitoring exercise, Bran disappeared.

Bran may never be found

Staff at the Irish Sea Sanctuary in Dublin, where the satellite was attached, admit the disappearance is a mystery.

Emma Higgs, Animal Manager at the centre, said: "There are a number of explanations - the most likely one is that Bran has lost the satellite.

"Alternatively he could be in fresh water where the satellite will not transmit, his fur might have moulted and the equipment has disappeared with his winter coat or he might have gone on to the beach or rocks where again the transmitter will close down out of the water to preserve its batteries."

Bran was released from the Dublin coast and into the open sea on 27 June.

He made his way to Wexford and then double-backed to Dublin.

Mull of Kintyre

But it was not long before he ventured further afield and was next tracked near Belfast and then at the Mull of Kintyre.

The last recorded link the sanctuary had with Bran was on 11 July when he was heading towards Colonsay.

Using three satellites to collect data, scientists had been able to watch the 3ft male's every move.

The aim of expensive project was to learn more about the shy grey seal's diving and travelling habits.

The Irish Seal Sanctuary had been Bran's home for the previous six months after he was rescued with serious internal bleeding.

Sanctuary staff kept a watch on Bran

Its chairman, Terry Flanagan, said: "He was doing so well. We are devastated but desperately trying to keep our hopes up."

Mr Flanagan said anyone who finds the tracking device or who thinks they might have spotted Bran - sporting a huge glue patch on his back - should get in contact.

Residents on Colonsay have already joined the hunt for the missing seal.