Question

A result of harmful fishing practice where part of the catch is discarded and not used is called overfishing

 supertrawling

 bycatch

 longlining

I think its either by catch or over fishing

Answer 1

A result of harmful fishing practice where part of the catch is discarded and not used is called Bycatch.

Answer 2

When part of the catch is discarded and not used is called a "bycatch". This occurs when other, usually smaller fish, get caught by accident by fishermen hoping to catch other kinds of fish.