Due to the heavy human populations and high level of industrialization along its shores, the wildlife of the North Sea has suffered from pollution, overhunting, and overfishing. Flamingos and pelicans were once found along the southern shores of the North Sea, but became extinct over the second millennium. Walruses frequented the Orkney Islands through the mid-16th century, as both Sable Island and Orkney Islands lay within their normal range. Gray whales also resided in the North Sea but were driven to extinction in the Atlantic in the 17th century Other species have dramatically declined in population, though they are still found. North Atlantic right whales, sturgeon, shad, rays, skates, salmon, and other species were common in the North Sea until the 20th century, when numbers declined due to overfishing.