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This year, it appears they have become ``almost prolific'' along the coastline, and a University of Otago marine ecologist is calling them ``sentinels of climate change''.
Dunedin recreational fisherman Brent Russell caught a 72cm kingfish at the weekend near Quarantine Island.
He was delighted with the rare catch, but put it back because it was 3cm short of the legal size.
``The last caught in the harbour that I'm aware of was a small one in 2015,'' he said.
Commercial fisherman Allan Anderson, of Karitane, said he and his son had been set-netting off the coast of Karitane for years, but in the past few years, kingfish had become much more common.
``We would catch maybe one or two in a summer season 10 years ago. We're catching one or two every day now, if not 10 sometimes.
``Twelve is the most we've caught in a day.
``It's been something that's been turning up in our waters more regularly every year. They're becoming almost prolific.''
He said they were set-netting more than 4 nautical miles off the coast, but kingfish preferred the waters closer to the coast.
He believed there was potentially even more of them closer to shore.
``We're only on the fringe of what's truly there.''
Kingfish are most abundant in the northern half of the North Island, and can grow to more than 1.5m and weigh more than 30kg.
University of Otago marine ecologist Prof Steve Wing said the fish were becoming more prevalent in southern New Zealand because the water was getting warmer.
Coastal water temperatures were between 2degC and more than 6degC above average at the moment.
``One of the things we are seeing now are a lot of the species we associate with sub-tropic waters. They are showing up further south than we normally see.''
He had also heard reports of kahawai being caught around southern parts of New Zealand and snapper being caught in Fiordland this year.
``Those fish are real sentinels for what's going on.
``They show sub-tropical waters are here and they indicate a larger, physical change is going on.
``This is what we expected to happen in a warming ocean.
``This is one of the things we expected to see under climate change.''
A Niwa meteorologist said La Nina was causing much of the water heating this year.
It brought large ridges of high pressure to the atmosphere across the Tasman Sea and over New Zealand, resulting in sunny, warm weather and tranquil seas.
Without storms to mix up the sea, the surface layers of the ocean had warmed up quite dramatically.
Prof Wing said sea currents were causing sub-tropical water to move south.
``The waters are so warm because we've got this big injection of sub-tropical waters into the Tasman and it's coming up along the Southland Current.''
He said it was difficult to know whether it was a one-off event or would continue into the foreseeable future.
``The ocean is quite variable from year to year. We have observed in the past, warm periods and cool periods.
``But the overall trend - the trend over 50 years - is that our winter-time temperatures are increasing.
``What that means is the sub-tropical water that's normally here in the summer is spending more time here in the winter, as well.
``Overall, the temperatures are increasing.''
Prof Wing said there would be ``winners and losers'' during climate change, and it might not be ``all bad'' for everyone.
``Things will be different - it's the only definitive thing we can say. It's not necessarily all bad.
``There will be some changes that are quite dramatic in some places, and in some places it will be quite bad.
``For us, there may be some improvements. There will be some services that we didn't get before, like catching kingfish off our coast.''
However, Mr Anderson said it was an issue that was now costing commercial fishers thousands of dollars each season.
Each time a commercial fisher netted a kingfish, they were fined because there was no quota this far south to catch them, he said.
``The water temperatures are rising and kingfish are changing their habits when looking for food sources.
``The right sort of food is abundant here and the kingfish are chasing it.
``There's no quota in the area for kingfish because there's been no previous history of catching these fish.
``Some of the boats are paying over tens of thousands of dollars per season in fines.''
He hoped the Government would introduce a quota for kingfish in the area to ease the financial strain on commercial fishers.