 One of the early difficulties encountered was that the captive stock of the early 1990s was found not to be pure . It was discovered through DNA analysis that the captive population contained a number of animals that were hybrids with C. nubila caymanensis . The program contains only pure specimens , as these hybrids were sterilized by means of hemipenectomies and hence excluded . This program was created to determine the exact genealogies of the limited gene pool of the remaining animals and DNA analysis revealed that the entire North American captive population was descended from a single pair of animals . After five years of research two captive breeding populations were established and are managed as a single unit , with cross @-@ breeding between the populations to promote genetic diversity . 
