Mystery Incident
© Stuff.co.nzFish Supper: A seagull feasts on one of the hundreds of snapper washed up on Oneroa Beach.

The Ministry of Fisheries is asking for help from Waiheke residents after hundreds of fish were washed up on one of the island's beaches.

Walkers on Oneroa Beach last Thursday were stunned to discover dead snapper "every couple of steps".

While seagulls enjoyed a five-star feast, an honorary fisheries officer visited the beach to count and check the size of the specimens.

Ministry field operations manager Greg Keys says the incident is under investigation but there are many possible causes.

To rule out one possibility - whether the fish had been poisoned by algae - some of them will be tested for poison.

But Mr Keys says the fish could have escaped from a split net from a commercial fishing boat. Mr Keys says he has heard reports of similar occurrences on the Coromandel.

"It can happen accidentally from split nets or when there are too many fish and they spill over the side of the net, or the fishing boat might dump them."

Meanwhile, Department of Conservation marine ranger Guy Toogood says he understands the fish were too small to have come from a commercial take.

"It's thought to have been recreational dumping," Mr Toogood says.

"There is no information on who has done it but investigations are ongoing."

Because the dead snapper were concentrated at Oneroa Bay, Mr Keys says the fishing boat must have been quite close to that location.

And because commercial fishing boats don't have to report such incidents it is difficult for the ministry to discover who was at fault, which is why it is asking residents for help with its inquiries.

Anyone who saw a boat early on Thursday morning last week, and can give a description of it, should phone the ministry on 0800 4 poaching.