'Very rare' tropical fish spotted in Bay of Islands

A huge tropical fish has been spotted in the Bay of Islands after an unusually warm season.

The giant grouper, also known as the Queensland grouper, is one of the biggest bony fish in the ocean. It's only been sighted five or six times in New Zealand.

Paihia Dive skipper Ben Brodie snapped some photos of a member of the protected species swimming in the wreck of the HMNZ Canterbury in Deep Water Cove on Sunday morning.

'Very rare' tropical fish spotted in Bay of Islands
Photo credit: Ben Brodie/Paihia Dive

Fully-grown groupers can reach three or four metres in length and weigh up to 200kg. The fish spotted in the wreck of the Canterbury was a juvenile and almost one metre long.

Craig Johnston, owner of Paihia Dive, says he's never seen a Queensland grouper in more than 20 years of diving in New Zealand waters.

"It is very, very rare to see them."

He regrets that he wasn't diving when the fish was spotted, but went out to Deep Water Cove himself on Monday hoping to catch a glimpse for himself.

"They like caves and dark places, so we're hoping it hangs around."

'Very rare' tropical fish spotted in Bay of Islands
Photo credit: Ben Brodie/Paihia Dive

Mr Johnston says the Bay of Islands has had a highly unusual season, with sea temperatures up to 4degC warmer than normal. In August 2017 the temperature reached 20degC, up from 17degC which is typical for early spring.

"I've never seen a season like this," he says.

The "marine heatwave" has brought more tropical fish into New Zealand waters, and Paihia Dive has had sightings of rarely-seen species such as the sergeant major damselfish.

Mr Johnston says he's not sure whether the warm season is the result of climate change, as the previous summer was slightly colder than average.

"It's hard to say, I'm not a scientist."

In March several species of rare tropical fish were sighted at the Kermadec Islands 1000km north of New Zealand, which experts said was due to warming oceans.