When his large, powerful yacht slowed to a virtual stop, Olivier de Kersauson knew he had a problem. "I saw two arms, twice the size of my arm, grabbing the rudder." A giant squid had got caught in the propeller. "It had a lot of power and started to shake the boat." It was a sight Dr Steve O'Shea would love to have witnessed. For over 30 years he's been chasing the rare creatures. But recently, he's become aware of a disturbing trend. "Squids are incredibly good barometers of environmental health", he explains. "If I go back 10 years, I had 23 giant squids in one year. Now, because of the intensity of fishing, it's tailed down to one a year."