Fish rising to bait in warm seas
More snapper sightings, other species struggling
The seas around New Zealand were the warmest on record in 2018, and the changing ecological battleground has Kiwis’ beloved snapper rising to fishermen’s bait ahead of all other species.
In Auckland’s Hauraki Gulf, the casualties of warm seas appear to be tarakihi, gurnard, trevally, ha¯ puku, 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 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.
“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. 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 Niwa, the average sea surface temperature for last year was 15.6C — 0.87C above the 1982-2010 longterm 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 — many 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, Talley’s commercial fisherman Chris West said the fishing of snapper in places such as Tasman Bay off Nelson is “fat and healthy”.
West believed 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 began in the first week of November, and had been shortened by warming sea temperatures. Once it gets above 19C in December or January, snapper begin to disappear from Tasman Bay. However, a second spawning season begins in autumn, as snapper fatten up for winter, and that has been prolonged by warming seas.
Sanford commercial fishers chief operating officer Clement Chia said the company acknowledged climate had a negative impact on its bottom line in 2018.
Its annual catch was 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 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 subtropical species have new pests or diseases.”