bycatch

Any fish (or other creatures) that are not targeted as a catch but are unintentionally caught, and often discarded back into the sea.

Some offer him bags of bycatch—fish too small or net-mangled to sell, rays and seahorses few will want, and so on.

Any person, animal, or thing, captured unintentionally on camera or film.

To catch unintentionally while fishing for something else.