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.
"Because of this idiot, this pup had to be [rightly] shot by DoC."
Normally when a pup was on the beach, the mother would be foraging at sea and would soon return. However, in this case they did not know where the pup had been snatched from so they could not return it.
The pup was "extremely stressed and hypothermic".
"I am ashamed as a New Zealander that they [tourists] had to witness such a senseless act while on holiday," Ms Luecht said.
The offender was a dark-haired, average to tall man in his late teens or early 20s.
DoC Hokitika operations manager Ian McClure said the incident was disturbing.
The department was conducting an investigation and welcomed any information.
DoC actively promotes a safe approach distance (20m) from fur seals.
The New Zealand fur seal was nearly hunted to extinction in the early 1800s. Seals were given full protection in 1978 under the Marine Mammals Protection Act. The number of seals today is only a small percentage (10-15 per cent) of the numbers that used to live around New Zealand in the early 1800s.
