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Danielle Gibas, sightings officer, Sea Watch Foundation, believes it was a rare sighting of a harbour porpoise in the Mersey.

She said: "Harbour porpoises are notoriously difficult to spot. They surface fleetingly and have such a small dorsal fin that it is often confused with ripples or waves in the water. Contrarily to dolphins, porpoises rarely leap out of the water so you have to be very lucky to notice them at a glance.
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