bycatch

Short definition from Wiktionary

Noun

1. 1
   Any fish (or other creatures) that are not targeted as a catch but are unintentionally caught, and often discarded back into the sea.
2. 2
   Any person, animal, or thing, captured unintentionally on camera or film.

Verb

1. 1
   To catch unintentionally while fishing for something else.