Robin McKie in London
ON the North Sea floor, off the Farne Islands, scientists have discovered a mysterious gathering place for grey seals. It is the aquatic equivalent of a favourite country pub. Some seals will swim hundreds of miles through murky seas just to visit it.
The discovery has baffled researchers, who cannot explain why so many seals from different colonies continually head for this tiny spot. Nor can they explain how they navigate, flawlessly, through pitch- black water to reach a featureless stretch of gravel on the sea floor.
“Seals head for this zone almost as if it were a magnet,” said Professor Mike Fedak, of the Sea Mammal Research Unit at St Andrews University. For several years, the unit has been studying grey seals, which have major colonies on the Farne Islands, off the coast of Northumbria, the Isle of May and Orkney.
Originally stymied by the fact that seals spend most of their lives under water, the researchers built tiny computers to measure a seal’s diving ability, swimming speed, and direction of movement. These were attached to transmitters and the units glued to the heads of various, startled seals.
A switch is triggered when the unit is exposed to air, and data from the seal’s previous dive is beamed to orbiting satellites that relay the signals to the unit.
This research produced two major surprises. It revealed that seals could navigate with unerring accuracy. The second surprise came when the scientists combined the tracks of several Farne seals, and found nearly all headed for the same part of the sea, a few miles off the islands. The researchers called this spot the Farne Box. Seals would head there, and spend their time diving to the bottom, though their purpose remains obscure.
Last month, the team began monitoring another colony miles away and fitted seven seals with transmitters. At first, the animals moved only a few miles away from their islands, details of their underwater activities being relayed to the unit as tracks displayed on their computer screens.
“Suddenly a couple of seals peeled away and headed south on separate courses,” said Fedak. “We didn’t think too much about them – at first.
“Then, as we watched, they headed straight to the Farne Box.”
Two other animals subsequently made the Farne Box trip, suggesting the site has all the sealy appeal of a holiday beach.
Why? Geologists say there is nothing remarkable about the seabed there – although it does have gravel banks, and these provide homes for sand eels, a favourite seal snack. But there are thousands of gravel banks under the North Sea.
“It is very likely food has got something to do with this strange activity,” added Fedak. “Seals don’t waste energy if they can help it.”
Scientists point out that baby seals are left to fend for themselves three weeks after they are born, with grim results. Half of all seal deaths occur during the next few months of their lives. It may be that their first successful feeding place gets imprinted in their memories so they can return to it, like homing pigeons, in hard times.
But, researchers say, it’s still all speculation. The attraction of the Farne Box to seals is still a mystery.