Snapper rising to the fisherman's bait in NZ's warmer oceans, as other species sink

Hardy snapper are adjusting to warmer waters but other species are not as resilient. Photo / Steve Doak

The seas around New Zealand were the warmest on record in 2018, and the changing ecological battleground has Kiwis' beloved snapper rising to fishermens' bait ahead of all other species.

In Auckland's Hauraki Gulf, the casualties of warm seas appear to be tarakihi, gurnard, trevally, hāpuku, and john dory, which are being caught in dwindling numbers according to marine health lobby group LegaSea's Sam Woolford.

"Everyone loves snapper and they're a great fish and they're really delicious, but when it comes to their feeding habits they're really voracious feeders, so they can easily fit in different areas within the food chain," Woolford said.

"Something like a trevally which feeds predominantly on crustaceans and animals on the sea floor, it's not as adept at change.

"Snapper are a lot more hardy, the same sort of thing applies to kingfish as well. So those would be the two that I'd say recreational anglers have seen.

"I wouldn't say there's more fish in the water but those are the fish that are coming into the boat more frequently."

According to data provided by the National Institute of Water and Atmospheric Research (Niwa) the average sea surface temperature for last year was 15.6C - 0.87C above the 1982-2010 long-term average.

Niwa's fish population estimates also back up assertions about the dearth of marine life in New Zealand oceans.

Based off "initial biomass" - a measure of total fish numbers pre-commercial fishing - a litany of well known species are dwindling around the "overfished" 20 per cent mark.

Given that 100 per cent is pre-commercial fishing population numbers, even snapper sits somewhere between 23 and 27 per cent.

However, Talleys commercial fisherman Chris West says the fishing of snapper in places such as Tasman Bay off Nelson is "fat and healthy"West believes the gradually warming waters around the top of the South Island have contributed to a longer optimal spawning period - with waters around 18C - for snapper.

"I imagine it will be positive because of warmer temperatures - that's why they've got such a robust fishery up north [in the Hauraki Gulf]. The further north you go the bigger the snapper fisheries are," West said.

"I personally think the warmer your waters, for longer, can only be a good thing. We are seeing really large numbers of juvenile fish as well."

West said an initial snapper spawning season consistently begins in the first week of November, and has actually been shortened by warming sea temperatures - once it gets above 19C in December or January, the snapper begin to disappear from Tasman Bay.

However, there is a second snapper spawning season that begins in the autumn, as the snapper fatten up for winter, that has been prolonged by warming sea temperatures.

Sanford commercial fishers chief operating officer Clement Chia said the company acknowledged that climate had a negative impact on their bottom line in 2018, with their annual catch down 5.6 per cent.

"Climatic intrusions had a meaningful impact on the supply side of the business and a consequential flow through to our bottom line. Total wild catch and farmed volumes were down from approximately 125,000 tonne to approximately 118,000 tonne," Chia said.

He said Sanford's salmon farming off Stewart Island and its harvest of greenshell mussels around Marlborough Sounds were particularly hard hit by warmer waters last year.

Niwa chief scientist Andrew Forsythe said it was too early to extrapolate the full effects of warming New Zealand seas on marine life, but people could expect to see species retreating from traditional habitats.

"As the ocean temperature rises, certainly the optimum zones for different species will shift, and you may see species that are subtropical have new pests or diseases may have incursions that go further afield."