Environmental DNA surveys and the following physical field surveys suggest that small headwater streams likely serve as important habitats for juveniles and larvae. While habitat degradation threatens the Japanese giant salamander, it can inhabit disturbed streams surrounded by agriculture fields such as rice paddy fields. Adults appear to do well in a stream surrounded by rice paddy fields because rice paddy fields provide habitats for frogs, which serve as primary diet for adult giant salamanders in such a stream.
The passage highlights that while habitat degradation poses a threat to the Japanese giant salamander, it can adapt and survive in disturbed streams surrounded by agricultural fields like rice paddy fields. This is because these environments provide suitable habitats for frogs, which are a vital food source for adult giant salamanders.