most captive bred rays will have long tails. this is because in the wild, rays may get there tails damaged or they fall only in transport due to the lack of water. when the tail is out of water for too long, it will dry up and break off. But I have seen some rays born with naturally short tails, maybe it got broken off inside the womb??
This is why it is very uncommon for a WC ray to have a full tail unless it was inport carefully and at ayoung age. Hopes this helps.