"Incidental catch" includes the careless and unnecessary injury and killing of endangered and threatened species (e.g. Lynx), protected animals out of season (e.g. nursing mothers), unprotected animals anytime in almost any way (e.g. skunks)--and people's dogs.
Trapping regulations allow for a lot of slop in what happens after a trap is set (and left unattended to catch whatever is attracted to its lure and capable of tripping its mechanical trigger). These allowances for "incidental catch" make the unintended damage legal.
"Incidental catch" is a term used by trappers to refer to the animals they catch unintentionally (while trying to catch other animals).Trappers sometimes complain of unwanted animals "clogging up" their traps; that's incidental catch.
Look up "incidental" in the dictionary, and you find a word that makes unintended consequences seem unavoidable and acceptable.
Legally, unless clear intent is shown, the killing of our dogs is generally considered to be "incidental" to the activity of trapping. Even if a trapping regulation is violated, the fine is for the violation, not the death of the dog.