The Waddensea is teeming with life! Mussel banks and mudflats that arise from the sea at low tide form a rich area where large amounts of mussels, shellfish, worms, shrimps and plants make up a richly laid table for many birds and fish. Many North Sea fish use the Waddensea as a nursery while others live there year round. Marine mammals, such as the harbour seal, the grey seal and the porpoise, profit from the rich fish life in the Waddensea. The seals hunt in the sea at high tide and rest on the sandbanks at low tide. More than 30,000 harbour seals live in the Waddensea as well as over 2000 grey seals. The area is famous as both a breeding ground and winter fuel station for migrating birds. In total, 10-12 million migrating birds pass through every year, consisting of waders, geese, ducks and gulls.