'Rare' tropical Aussie grouper spotted in New Zealand waters after summer's marine heatwave

Tuesday, 29 May 2018

Giant Queensland grouper swimming at the wreck of the HMNZS Canterbury in Deep Water Cove.

A Queensland grouper was spotted swimming at Northland's Deep Water Cove, more than 3000 kilometres from its Aussie home, on Sunday.

Paihia Dive skipper and diving instructor Ben Brodie, 27, was guiding divers around the HMNZS Canterbury wreck when he spotted the rare tropical fish.

'We were just descending down to the bridge area and there he was, poking his head out of the top hatch of the bridge. I instantly recognised it was a grouper of some sort.'

Brodie later found out it was a rare Australian grouper. 'To find it, and get a photo of it, was really special. We were pretty stoked with it. Anything that's a rare visitor is really exciting.'

* The country will be warmer than normal in autumn

* We've just sweated through our warmest start to a year on record**

A marine heatwave started in November, sending summer sea surface temperatures soaring to as much as six degrees Celsius above average in the Tasman Ocean.

The Queensland grouper was protected in 2010. As the biggest reef fish in the world, a Queensland grouper could grow up to three metres long and weigh up to 600 kilograms.

The grouper investigating the HMNZS Canterbury wreck at Deep Water Cove.

Niwa principal scientist Dr Malcolm Francis, a fisheries biologist, has researched protected species for the Department of Conservation. He expected the Queensland grouper might have been carried along the warm water current running across the Tasman Sea from Australia, via Norfolk Island, and down the East Coast of New Zealand.

'The Queensland grouper is known to hang around under drifting seaweed and logs, so it could have come here with debris from tropical areas north of New Zealand. But also it's possible with very big animals that they could swim here under their own steam.'

It was 'pretty rare' to see Queensland grouper in New Zealand, he said.

'I've been able to find maybe a dozen records of them here before, but scattered over 20-30 years. It's pretty unusual. But because they're so big and spectacular, people take notice of them when they see them.'

The giant grouper was sturdy enough to head back up north if the New Zealand winter became too cold, Francis said.

Francis said it has been 'a good year for tropicals' because of the marine heatwave, but it was certainly not the first.

'We periodically have a lot of tropical fish in New Zealand, typically when it's a La Niña year,' he said.

'Some of them will survive the winter, and some of them will die. Some species never reach adulthood in New Zealand waters.'

Paihia Dive owner Craig Johnston has been diving in the area for 30 years, and said the 2017-2018 summer had the most consistently warm temperatures he had seen.

'We've seen a lot more tropical species than we normally would. It's made it quite interesting diving, especially this summer and autumn.'

Other rare species spotted this season included the black hairy dogfish, the Lord Howe Moray, the sergeant major damselfish, and lion's mane jellyfish.

Brodie agreed, adding that the more diverse tropical species coming to the area would hopefully contribute to ongoing discussions about fishing at Deep Water Cove.

The cove, in Maunganui Bay, has been protected by the local hapu (division of a Maori people or community), Ngati Kuta and Patukeha ki Te Rawhiti. It's called a Rahui (closure), and has been closed to all fishing except kina since December 1, 2010.

'It has been such a great area for juvenile fish in the nursery,' Brodie said. 'The local iwi are about to decide whether or not to keep it as a reserve or to open it up for fishing. Having these subtropical species come down is hopefully a great reason for it to stay a reserve.'