They are an introduced species with no natural predators here. Except us. There were strict regulations on the specifications for the containment fences the farmers were supposed to build but the agriculture ministry has admitted they have never made any attempt to enforce those regulations, so of course some escaped and they have done well for themselves in the wild. They destroy habitat and eat anything, including game like birds (young and eggs included) and fawns. SERM does not regulate them as a game species, they are a nuisance. No season, no bag limit, if you have permission to shoot on land (including the default permission that exists to shoot on Crown land if there are no bylaws or regulations against it) and you see a wild boar, it is legal to kill it as long as you are taking normal safety precautions.