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Researchers in Australia have discovered a secret weakness of one of the ocean's most impressive predators.

The scientists, who examined the retinas of 17 different species of shark, discovered that the creatures had only one type of colour-sensitive cell, known as a cone cell, in their eyes.

Using statistical analysis, researchers have demonstrated that the journeys of three species—tiger, thresher, and blacktip reef shark—were not made by accident; the sharks followed some kind of path.

Scientists analysed data from tiger sharks tagged with acoustic transmitters and found they took directed paths from place to place. Other species, such as blacktip reef or thresher sharks, did not show this behaviour.

However, Swedish Navy spokesman Capt. Bo Rask said Thursday there were no signs the submarine had been damaged by weaponry, but a metal wire

The submarine, a Whiskey-class vessel from the 1950s that was once common in the Soviet navy, was discovered by chance during a seabed survey.

The wreck lies on the seabed in the Swedish economic zone. Some hope that the find will finally prove that Sweden were subject to repeated intrusions by former Eastern bloc submarnes during the 1980s.

A study by Simon Oliver at the School of Ocean Sciences, Bangor University describes the first observations of thresher sharks venturing into shallow coastal waters to interact with cleaner wrasse, a type of small fish that groom other fish species.

Thresher sharks live in the open oceans and much of the knowledge of them to date is based on fisheries bycatch. This study just published in published in PLoS ONE, (14 March 2011) examined the behaviour of these elusive sharks as they invite cleaners to remove parasites and dead tissue.