Climate change could spell ‘catastrophe’ for at-risk marine populations

As ocean temperatures continue to climb, even in the Deep South, Southland anglers are seeing bigger and more exotic fish than ever before.

For Ian Carrick, president of the Southern Sport Fishing Club, boating just got more interesting.

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

Twenty years ago, Carrick said, snapper was considered the “fish of the North Island”, whereas kingfish were not commonly seen around the Southland until six or seven years ago.

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Now they are increasing in size and can be caught all around Stewart Island and Fiordland, he said.

“Having more resident kingfishers means the water needs to be continuously warmed,” he said.

“We caught two striped marlin in Fiordland. Now, striped marlin in Fiordland, as far as I know, has never happened before… the waters have to be warm to get marlin, for no other reason. It shows that something different is going on there.”

It’s not an assumption Carrick relies on, his temperature gauge – used to fish along temperature lines – has been raised consistently during 20 years of fishing in the Southland.

Last summer it reached 19 or 20 degrees, while 10 or 15 years ago it would have averaged about 16 or 17 degrees, he said.

“It was a pretty extreme year, but over the last 10 years consistently, water temperatures have slowly risen,” he said.

University of Otago marine biologist Dr Bridie Allan said kingfish and cod were moving further south than usual in search of cooler waters and would compete with native fish such as blue cod for food.

For marine ecologists, this is a serious threat to rare coral and marine life.

“These big fish have very high metabolic rates, so they eat a lot.”

Smaller fish, such as spots often caught on southern shores, will face higher predation as they struggle to respond to new prey, he said.

Another major concern was that species could only move south before reaching latitudes where light would be limited.

“Some species need sunlight, so they can’t move south … you would hope they would adapt, but we don’t know the extent of climate change.”

“That’s why these marine heat waves are so important because they’re being masked by global warming.”

Marine heat waves are when water temperatures remain in the warmest 10% of historical observations for at least five days.

Allan cited this summer’s mass bleaching of sea sponges in Fiordland as an example of the effects of heat waves combined with climate change.

The discovery was made by a team from the University of Victoria after a prolonged heat wave in May in which water temperatures in the region were nearly five degrees warmer than normal.

Kingfishers, which were not commonly seen on New Zealand's south coast six or seven years ago, are becoming more common in the south.


Kingfishers, which were not commonly seen on New Zealand’s south coast six or seven years ago, are becoming more common in the south.

Professor James Bell, lead researcher on the project, said at the time it was the largest-scale and most bleached sponge in a single incident reported anywhere in the world.

“The mass bleaching event highlights once again how dramatically our oceans are changing due to global warming and climate change,” he said.

He said that the heat wave also affected other local marine species that were neglected.

Gemma McGrath, a marine mammal scientist and hector’s dolphin specialist based at Colac Bay in western Southland, said climate change, along with other environmental factors, was halting dolphin population growth.

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

Ross Trafford/Supply

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

The dolphin population in the Catlins has fluctuated by about 40 dolphins over the years, indicating the population is not increasing despite conservation measures, he said.

The arrival of new fish in the area also brought an increased amount of prey, which made the Hector vulnerable in its small shells, McGrath said.

There were a lot of orcas around Colac Bay during the past summer, he said, with increased numbers seen in February.

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

A study released last month by Massey University detailed that whale sightings around northern New Zealand will decrease as oceans warm, leaving the South Island and Sea Islands more suitable habitat.

“They [dolphins] All this time they have to deal with the natural level of predators, which is just a part of life. But that’s a different kettle of fish for them. It’s a human-caused threat, and it’s higher than what predators do,” McGrath said.

McGrath was also concerned about the effect of warming oceans on Hector’s breeding habits.

“A female gives birth every two to three years, then the conditions are good. They don’t start breeding until they’re about six years old, and that’s when conditions are good,” he said.

McGrath walks along the beach at Colac Bay with her 10-year-old son Tamati.  The added pressure of climate change will ultimately have unknown effects on dolphin reproductive behavior, he says.

Robyn Edie / Stuff

McGrath walks along the beach at Colac Bay with her 10-year-old son Tamati. The added pressure of climate change will ultimately have unknown effects on dolphin reproductive behavior, he says.

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

NZ King Salmon cut its forecast profit for 2022 by $4-5 million as rising sea temperatures caused more salmon losses, while Sanford chief executive Peter Reidie said in January the water at the Big Glory Bay Salmon farm was warmer than usual. had a certain effect on the death of salmon.

CRA8 Rock Lobster Industry Association chief executive Malcolm Lawson said warming waters were an important factor to watch.

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

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

Rock Lobster species in the CRA8 area were able to adapt to the changing temperatures, Lawson said, they just needed time to acclimate.

He had seen no evidence of lobsters moving away from the area, as is currently happening in the US Gulf of Maine, but he had noticed some lobsters becoming lethargic.

This was because warmer waters carried less dissolved oxygen, jeopardizing the survival of live exports, if not fatally.

The industry has been adapting by using tanks with increased water flow to increase dissolved oxygen after the lobsters are caught, but as Lawson notes sea heatwaves, the summer fishery may have to be suspended.

“So if we get to the extremes … we’re not seeing anything like the Gulf of Maine yet.”

That’s still the buzzword, with research from the Deep South Challenge and NIWA predicting New Zealand’s 2,100 marine heat wave days will increase from around 40 at present to between 80 and 170 days a year.

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