Found primarily in the North Atlantic and the Baltic and Mediterranean Seas, European eel face a unique set of survival challenges. They have a fascinating development cycle, which begins with their birth out at sea and continues in freshwater streams thousands of miles inland, where they can grow to a length of 4.5. When they reach sexual maturity, at anywhere from 6 to 30 years of age, they return to the sea to spawn. If their route to the sea is blocked, they return to freshwater and can live for 50 years. But if they make it back to salt water and reproduce, they die. Because of this unusual life cycle, any eel that is caught at sea is a juvenile that has not yet had a chance to spawn. This has resulted in catastrophic overfishing of the European eel, and a critically endangered rating from IUCN.