The Department of Conservation had to shoot a fur seal pup after someone put it on the back of a motorbike while skylarking on the Hokitika beach and then dumped it away from its mother.
DOC is investigating the incident, which occurred on Saturday, and warned that it was an offence punishable under the Marine Mammals Act, with a penalty of up to $250,000 or two years in jail.
Hokitika resident Sabrina Luecht, a "wildlife rehabilitator", said tourists saw the young, unweaned fur seal pup being driven around on the back of a speeding 4WD quad bike along the beach before it was dumped on the Hokitika spit.
Ms Luecht went to locate the pup, which a "lovely Australian family was standing guard" over.
"I even saw the offender [still doing wheelies in the sand], who sped off upon sighting my running self.