Blue whales, the world's largest animal almost hunted to extinction in the 19th Century, are making a comeback in waters off New Zealand, scientists say. A study in the waters of the South Taranaki Bight, to the west of the country's North Island, showed blue whales were passing through in numbers greater than expected, researchers with the government's National Institute of Water and Atmospheric Research reported. The whales were taking advantage of an important food source there -- large clouds of plankton -- on their way to and from summer feeding grounds in Antarctica, the researchers said. "Conventional wisdom has been that blue whales only transit through New Zealand waters while migrating," NIWA marine ecologist Leigh Torres said. "But this new information suggests that this is not an accurate understanding of their ecology." Torres said the finding of blue whales present in the Bight with "some regularity and density" to feed would significantly enhance understanding of the distribution and foraging grounds of the elusive creatures in the Southern Hemisphere, Xinhua reported Monday. "Blue whales are huge and need to eat vast amounts of food, which are tiny plankton, to support their energy demands," he said. "But there are just four confirmed blue whale foraging grounds in the Southern Hemisphere outside of Antarctic waters. So, it's very important that we properly document and protect their foraging grounds."