The evidence came from an unusual dataset. Researchers at Bimini had DNA-sampled and tagged juvenile lemon sharks in the same lagoons for more than two decades, building a genetic register of who was born where. When adult females later arrived to give birth, parentage analysis matched some of them to juveniles sampled at that site years earlier.
This is natal philopatry, and it makes a nursery lagoon a fixed asset rather than an interchangeable patch of coast. Juvenile lemon sharks remain in shallow mangrove water for several years, where the water is too shallow for larger predators, before moving to reefs.
The consequence is unforgiving. If a mangrove lagoon is dredged or filled, the females that would have returned there do not simply relocate, and part of Bimini's own nursery habitat has been lost to development. The lemon shark is now assessed as Vulnerable.