Global Warming & Climate Change News Desk – Research involving in-water and baited camera surveys conducted between 2008 and 2023 indicates that populations of eastern blue groper have decreased by approximately 50% between Taree and Shellharbour. Fish numbers remain more stable on deeper offshore reefs; however, marine scientists warn that climate change is likely driving the species further south.

What’s next?

The NSW government is close to revealing whether a 12-month trial ban on all forms of blue groper fishing will continue.

Numbers of Eastern Blue groper — the state fish of New South Wales — have halved around the Sydney coast since 2008 and are in decline at shallow inshore reefs along the NSW coast.

But populations of the groper (Achoerodus viridis) are more stable at reefs in cool, deep water and strongest along the southern coast, according to a study published in Marine and Freshwater Research.

Its findings suggest shifts in eastern blue groper abundance, estimated using diver surveys and baited camera footage from 2008 to 2023, and could be driven by warming oceans due to climate change.

The research indicated that fishing pressure around Greater Sydney did not affect the current abundance of fish in that region.

A recent study conducted in collaboration between the NSW Department of Primary Industries and Regional Development and the University of Tasmania has been published. This comes at a time when the NSW government has not yet made a decision regarding the continuation of a 12-month trial ban on all methods of fish catching.

Study co-author Neville Barrett, an ecologist at the University of Tasmania, suspects there has been a much bigger decline in the species over a longer period but researchers don’t have the historical records to make the comparison.

“I wish we had this data going back 100 years because I think we’d have a massive decline in abundance,” he said.

A friendly but tasty fish

There had been so much fishing pressure on the wrasse species that 50 years ago, there were concerns it could disappear altogether.

Long-lived fish species are particularly susceptible to overfishing, and the eastern groper — which scientists think could live more than 70 years — is no exception.

The “friendliness” of the fish with divers also makes it easy prey for spearing.

Spearfishing of eastern blue groper in NSW was banned in 1969, and commercial fishing was scrapped in 1980.

Catching groper with a line recreationally was also banned in 1969 before being reinstated in 1974.

Blue groper are a favourite of divers and snorkellers for their perceived “friendly” nature. (iNaturalist: Euan Thomas, Eastern blue groper, CC BY-NC 4.0)normal

Half a century later, in February last year, the NSW government announced it would once again bring in a total fishing ban for the groper.

This came after two illegal illegal spearing incidents that drew public condemnation.

Debate has raged since the rule change as recreational fishing stakeholders demanded scientific evidence to warrant the ban.

Past recreational fishing surveys have suggested a decline in anglers targeting the species.

An estimated 3,529 groper were landed in 2013–14. This dropped to 164 in 2021–22.

Female blue gropers are actually a greeny brown colour, but they turn blue when they change sex at about 10 years of age. (iNaturalist: Erik Schlogl, Eastern blue groper, CC BY-NC 4.0)normal

Dr Barrett said there was an ethical obligation to make sure the NSW blue groper population was sustainable.

How long it could take to build up blue groper numbers is a bit of an unknown, especially since the fish doesn’t breed as quickly as smaller species.

But Dr Barrett said 10 years was the kind of timeframe you would need for a monitoring program to see if there had been a marked effect from a management change on Eastern Blue groper.

“Personally, I would love to see [eastern blue groper] protected for a longer period of time to see if numbers can rebuild,”

Dr Barrett said.

“And maybe the government can set some trigger points, like if the numbers double, they can have some limited fishing again.”

The NSW Department of Primary Industries and NSW Agriculture Minister Tara Moriaty’s office declined to comment on the new study before an impending announcement about the trial ban’s future.

Fish moving further south

Blue gropers living in four marine bioregions, which cover most of the NSW coast, were investigated for the study.

The Tweed-Morton Shelf, which extends from north of the Queensland border down to Coffs Harbour, had the lowest population of the species due to its warmer climate.

The Hawkesbury and Manning bioregions experienced a 50 per cent decline throughout the study. However, the deep, more astonishing reefs in the Manning bioregion harboured many gropers.

Sites along the NSW coast where underwater visual censuses and baited remote video camera surveys were conducted. (Supplied: Marine and Freshwater Research)normal

The study also looked at crimson-banded wrasse (Notolabrus gymnogenis) and southern Maori wrasse (Ophthalmolepis lineolatus) and suggested there were fewer of those species than expected around Greater Sydney because of fishing pressure.

But a similar human-driven effect did not appear to affect the blue gropers in the same area.

The highest abundance of the blue groper was in the Bateman’s Bay bioregion, in the state’s south, where populations peaked in 2016, dropped in 2020, and have now started to climb again.

An eastern blue groper pokes its head out in Cabbage Tree Bay, NSW. (iNaturalist: Jackleophoto, Eastern blue groper, CC BY-NC 4.0)normal

CSIRO marine scientist Alistair Hobday, who was not part of the study, said the research backed up past predictions that blue groper would move further south because of climate change.

“The finding that they may also move deeper to find cooler water was also interesting and consistent with general predictions,” he said.

The blue groper has historically lived as far south as Victoria, where all fishing of the species was banned in 2011, but it has also started to be spotted in Tasmania.Loading…

Dr Hobday said having more groper in Tasmania could help reduce the rise in urchin barrens that wipe out kelp, dramatically changing the ecosystem balance.

“The fish is moving more slowly than the urchin, and building up population numbers of blue groper is thus important,” he said.

“I think this species is more valuable for its potential role in eating sea urchins than in being eaten by humans.”

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