Underwater visibility in the Foyle is very poor at the best of times making identification difficult.

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Even when the sharks are found closer to the ocean surface, they spend their time in the cool-temperature, plankton-rich waters that limit underwater visibility and make diving difficult.

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"The visibility underwater is amazing, " says Paul Irvine of Dehouche.

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Murray, who consulted the Cup's four competing teams, also recommended outfitting sailors with hands-free underwater breathing equipment, underwater-locator devices and high-visibility helmets.

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Eco enthusiasts can get their Jacques Cousteau on at Las Baulas National Marine Park, an underwater showcase of marine life with warm water, high visibility and gentle currents.

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We have individuals who when it's zero visibility like that, they will actually close their eyes because the eyes do nothing underwater when you can't see anyway.

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