For example, in the USA, crocodilians are protected by national and international legislation, preserved in National Parks, hunted in the wild and raised on farms and ranches. The Crocodile Action Plan would be a good place to start. Habitat is the common factor in the conservation of all species. For a tiny minority, hunting may be wiping out the species but that is almost always because habitat destruction has reduced the population so that it can longer support hunting. Species like the Chinese alligator, which will likely lose all its semi-natural habitat, pose a difficult question.
Captivity is only a very short term answer.
Domestic cattle and horses are among the most common ungulates, yet the wild species that gave rise to them are amongst the most endangered mammals. Most species of crocodilians, however, still have the potential to survive in the wild if we can develop balanced plans for the maintenance of their habitat. This means mapping habitat and determining the threats to that habitat. Sustainable use is only valuable if it fits into an integrated plan. The idea that making a few people economically dependent on crocodilians will ensure the crocodiles survival is ludicrous.