"Apparently Puffer Fish are not uncommon in NZ waters and you may occasionally find the odd one on the beach but rarely in large numbers like this," a post by Tonkin + Taylor said.
"One possible explanation is that they might have been caught in gurnard nets. Because puffer fish puff up when they are stressed or threatened, they might have floated in on the tide."
New Plymouth District Council workers visited this afternoon and could not see any of the carcasses still on the beach.
Council manager of customer and regulatory solutions Katrina Brunton said it was advisable for dog owners to still keep a close eye on their pets when walking on Fitzroy Beach as one or two fish could still be around.
"We haven't had any calls from dog owners about their animals being affected by the puffer fish," she said.
Niwa principal scientist for fisheries Dr Malcolm Francis said it was uncommon to hear of such a large number of the fish being washed up. However it was not uncommon for a couple to be found washed up on west coast beaches.
"It belongs to a group of fish that is lethal so it would be well wise to stay well clear of it."
Francis said if any of the puffer fish were still on the beach they would have probably degraded and decomposed enough not to cause a problem. "But certainly when they are relatively fresh, I would be a bit concerned about dogs. I can't imagine people eating them because they are very spiky and that would deter just about everybody I think."
He said puffer fish were occasionally caught in trawl nets put out by fishing crews and they could puff themselves up with water or air. "If they have got air inside them they float and when they get thrown back in the water they might just get blown ashore by the wind."