Climate change could spell ‘disaster’ for marine populations at risk

Anglers in the South are seeing bigger and more exotic fish than ever before as the ocean’s temperature gauge ticks up, even in the Deep South.

For Southern Sport Fishing Club president Ian Carrick, it makes boat trips all the more exciting.

Where blue cod was once the fish synonymous with Southland, snapper, kingfish and sometimes marlin are becoming more common in recreational catches.

Twenty years ago, snapper was considered a “North Island fish,” Carrick said, while kingfishers were only seen in Southland six or seven years ago.

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Now they are getting bigger and can be caught anywhere around Stewart Island and Fiordland, he said.

“The fact that kingfish are becoming more resident means the water has to be constantly getting warmer,” he said.

“We had two catches of striped marlin at Fiordland. Striped marlin in Fiordland, as far as I know, has never happened before… to get marlin the water has to be warm, there is no other reason for it. That shows that there is something else going on out there.”

It’s not just a hunch that Carrick relies on, his temperature gauge – which is used to catch fish along temperature lines – has risen steadily in his 20 years fishing in Southland.

Last summer, the meter hit around 19 or 20 degrees Celsius, while 10 or 15 years ago it would have averaged about 16 or 17 degrees, he said.

“This has been a pretty extreme year, but over the past 10 years, water temperatures have just been rising slowly,” he said.

The marine biologist Dr. Bridie Allan of the University of Otago said kingfish and snapper migrated further south than usual in search of cooler waters, competing with resident fish like blue cod for food.

For marine ecologists, it is a worrisome threat to rare coral and marine life.

“These bigger fish have very high metabolisms, so they eat a lot of food.”

Smaller fish, such as spotties, often caught on the south coast, would face higher predation rates because they struggled to respond to the new predators, she said.

The other big concern was that species could only move so far south before reaching latitudes where light would be limited.

“Some species need sunlight, so they can’t move further south… you’d hope they’d adapt, but with the speed at which climate change is happening, we just don’t know.”

“That’s why these marine heat waves are so important, because they’re covered in global warming.”

In marine heat waves, water temperatures remain in the warmest 10% of historical records for at least five days.

Allan pointed to the massive bleaching of sea sponges in Fiordland last summer as an example of the impact heat waves coupled with climate change can have.

The discovery was made in May by a team from Victoria University after a prolonged heat wave that saw water temperatures about five degrees warmer than normal in the area.

Kingfish, usually not seen around New Zealand's south coast six or seven years ago, are becoming more common in the south.

SIMON O’CONNOR/Stuff

Kingfish, usually not seen around New Zealand’s south coast six or seven years ago, are becoming more common in the south.

The project’s then-lead researcher, Professor James Bell, said that to his knowledge, it was the largest scale and number of sponges bleached in one event and reported anywhere in the world.

“The massive bleaching event shows once again how dramatically our oceans are changing as a result of global warming and climate change,” he said.

The heat wave may also have affected other native marine species that had gone undetected, he said.

Marine mammal scientist and dolphin expert Gemma McGrath, based in Colac Bay in western Southland, said climate change combined with other environmental factors had stunted dolphin population growth.

Hector's dolphins have previously been filmed engaging with paddleboarders in Southland's waters.

Ross Trafford/delivered

Hector’s dolphins have previously been filmed engaging with paddleboarders in Southland’s waters.

In the Catlins, the dolphin population has hovered around 40 dolphins for years, indicating that the population was not growing despite conservation measures, she said.

The arrival of new fish to the area had also brought in more predators, making Hector’s vulnerable in their smaller pods, McGrath said.

There had been quite a few orcas around Colac Bay this past summer, she said, and more and more killer whales were sighted in February.

Orcas, also known as killer whales, are found in all oceans but are most common in colder waters near Antarctica, Norway and Alaska.

A Massey University study released last month indicated that as the oceans warmed, whale sightings around New Zealand’s north would decline, with the South Island and Offshore Islands becoming more suitable habitats.

“She [dolphins] are dealing with a natural level of predators all this time, which is just part of life. But this is a different story for them. It’s a man-made threat, much better than what predators do,” McGrath said.

McGrath was also concerned about the impact warming oceans could have on Hector’s breeding habits.

“A female will give birth every two to three years, and then the conditions are good. They don’t start breeding until they are about six years old, and then the conditions are good again,” she said.

McGrath walks along the beach at Colac Bay with her son Tamati, 10. She says the added pressures of climate change will eventually have unknown effects on dolphin breeding behaviour.

Robyn Edie / Stuff

McGrath walks along the beach at Colac Bay with her son Tamati, 10. She says the added pressures of climate change will eventually have unknown effects on dolphin breeding behaviour.

“That’s the thing about climate change, it’s the added pressure … we don’t know what impact it could have.”

NZ King Salmon cut its forecast revenue for the year 2022 by $4 to $5 million due to higher salmon losses caused by rising sea temperatures, while Sanford chief executive Peter Reidie said warmer-than-normal water at his Big Glory Bay Salmon Farm in January had some impact. had on the salmon mortality.

CRA8 Rock Lobster Industry Association chief executive Malcolm Lawson said warming water was a key factor monitoring it.

The Rock Lobster fishery in New Zealand is divided into 10 different management areas.

The CRA8 fishery is geographically the largest on the mainland, stretching from Long Point in Otago to Stewart Island, the Foveaux Strait and along the coast from Fiordland to Bruce Bay.

The Rock Lobster species in the CRA8 area were adaptable to changing temperatures, Lawson said, taking only time to acclimate.

It hadn’t seen any evidence of lobsters moving out of the area, as is currently happening in the Gulf of Maine in the United States, but had noticed some lobsters emerging lethargic.

This was because warmer waters contained less dissolved oxygen and, while not fatal, could compromise the survivability of live animal exports.

The industry was adapting and using tanks with increased water flow to increase dissolved oxygen after lobsters were caught, but Lawson noted that due to heat waves at sea, fishing may need to be limited in the summer.

“That’s when we go to the extreme … we don’t see anything like the Gulf of Maine yet.”

Still, the key word is, as research from the Deep South Challenge and NIWA predicts that by 2100 the number of heat wave days at sea in New Zealand will increase from about 40 currently to between 80 and 170 days per year.

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