U.S. Fish & Wildlife Service officials say they have to curb the backyard breeding of desert tortoises because the growing population of unwanted pet tortoises diverts resources from efforts to preserve the species in the wild.

Mike Senn, assistant field supervisor for the Fish &Wildlife Service in Nevada, told the Las Vegas Review-Journal that it can be “a really difficult issue” to explain to people. He said simply breeding more tortoises won’t save the species if not enough is done to improve and protect natural habitat and address threats in the wild.

Captive tortoises threaten native populations because they can carry diseases with them when they escape or are released illegally in the desert.