The world’s rarest whale is believed to have washed ashore on a New Zealand beach, the country’s conservation authority said on Monday. The whale is so rare that since the 1800s, only six specimens have ever been known to science, the Department of Conservation (DOC) said. The 5-metre long whale, found on July 4 on a beach near Dunedin in the South Island, was believed to be a spade-toothed whale, DOC Coastal Otago operations manager Gabe Davies said. “Spade-toothed whales are one of the most poorly known large mammalian species of modern times,” Davies said. “From a scientific and conservatio…