Seals have surprised scientists with their astonishing prowess as navigators.

During recent investigations using radio-tagged seals in the North Sea, researchers found the animals could swim, even underwater on murky winter nights, in straight lines over long distances."We were tagging one seal as he lay about on the Farne Islands off Northumberland," said Dr. Michael Fedak of the Sea Mammal Research Unit, Cambridge. "He started off straight towards the Isle of May, a popular seal sanctuary, to the northeast. We joked that he knew where he was going. To our amazement, he maintained a continuous straight line all the way to the island.

"In deep, cold, almost pitch-black water, with no possible visible clues, the seal swam unerringly for 40 miles and came straight out at his destination. We were absolutely amazed."

Further monitoring convinced the group that the seal was following a deliberate pattern. He swam directly to the Firths of Forth and Tay before swimming straight back to the Farne Islands.

"It is a complete mystery how seals can do this sort of thing," Fedak said, "Perhaps they have some kind of internal compass or have detailed memories which allow them to navigate in these conditions."

The unit's discovery is part of research aimed at establishing how destructive seals are to Britain's fishing industry. Fishermen say they cause millions of dollars of damage to nets and traps. Conservationists describe these claims as extreme exaggerations.

To establish the truth, biologists tried to tag seals with radio collars. "Unfortunately, their necks are broader than their heads and the collars just slipped off," Dr. Fedak said.

However, researchers developed a powerful seawater resistant glue that has allowed them to stick radio transmitters on top of seals' heads.