Why are standard large-scale removal techniques often ineffective against established Wels catfish populations?

Answer

They tend to inhabit deep holes and feed nocturnally

The species' inherent difficulty for large-scale assessment or removal stems from its tendency to reside in deep holes and its habits of feeding primarily during the night, making standard netting or electrofishing less effective.

Why are standard large-scale removal techniques often ineffective against established Wels catfish populations?
EcologyanimalinvasivefishCatfish