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By Bron Willis 26 May 2022 6 min read

redleg banana prawns
CSIRO worked with fishers in the 2015–16 El Niño to understand the cause of reduced catches of redleg banana prawns. Image: Dwayne Klinkhamer

In 2015, CSIRO Senior Principal Research Scientist Eva Plaganyi was meeting with local fishers from the Northern Prawn Fishery, one of Australia’s major, multi-species fisheries which stretches from the Joseph Bonaparte Gulf and the Gulf of Carpentaria, when she heard a puzzling story from a local fisher.

“One of the fishers was saying ‘the tides were really weird this year. We didn’t catch many red leg banana prawns – there’s something odd going on’.”

Intel for fisheries from climate data

With 20 years’ experience bringing her passions of mathematics and conservation together, Eva turned to data from the local area to find an explanation.

“The first thing I did was pull out information on the tides, as well as satellite images of the temperatures and the mean sea level height in that area. There were some major anomalies,” Plaganyi said.

Eva’s work is part of CSIRO’s research on how climate change is affecting not just our oceans, but our fisheries and their ability to build a sustainable business in the face of changing seas. Using novel computer modelling tools, Eva and her colleagues quickly found the anomalies she noticed were representative of changes occurring right across the oceans of northern and eastern Australia that season.

The role of El Niño on fisheries

“The anomalies the fisher was seeing first-hand was part of the very large 2015–16 El Niño that affected so many of our fisheries around the coast at the Joseph Bonaparte Gulf and the north West of the Gulf of Carpentaria,” Plaganyi said.

“What happened is that El Niño basically caused a change in the local sea level – it dropped quite substantially.”

But the 2015–16 El Niño was not an isolated event. Australia’s tropical oceans are warming almost twice as fast as the average for the rest of the world. Waters off the south-east and south-west of Australia are hotspots for climate change impacts.

The challenge for Eva and her team was to work with fishers such as the Northern Prawn Fishery to develop a mitigation strategy and help them respond nimbly to major changes in the environment. Their answer was sophisticated modelling tools that are now setting fishers up to respond better when the next high-impact El Niño, for example, comes along.

Catches of redleg banana prawns being unloaded after being caught in the Joseph Bonaparte Gulf. Image: Phil Robson

Ecosystem modelling

Fellow CSIRO scientist Dr Beth Fulton works in a similar way, describing herself as an ecosystem modeller.

“I create mathematical models of the ocean and the animals in it, and how they change in response to pressure on the oceans – such as fishing or climate change,” Beth says. “We started looking at fisheries in general, but climate change became a part of what we had to consider in the 2000s. Now it’s just standard practice in any prediction we do with oceans: you’ve got to account for climate change.”

In recent years, CSIRO research led by Beth and Eva has outlined some startling findings.

“The waters around Australia are some of the fastest warming in the world, particularly the southern parts of Australia,” Beth says. “We have an ocean current called the East Australian Current (made famous by the movie Finding Nemo), which used to get to the corner of Victoria and then turn towards New Zealand. With climate change, that current has moved and now reaches Tasmania, many hundreds of kilometers further south.”

This has huge impacts on the movement of species.

“Animals that move either as larvae in the water, as tiny babies or adults who physically walk or swim, following the temperature signal – they end up in a different place," Fulton added.

Warming waters, moving animals

Beth cites over 100 new marine species that had never been recorded in Tasmania before 2003, thanks in large part to these warmer waters brought by changing ocean currents. These new species are restructuring the ecosystems – and while markets for some species may dwindle, markets for others may be created.

“There is now a fishery for an urchin called Centrostephanus rogersill, which was never in Tasmania before,” Fulton said. “That new fishery is there not only to make use of a new resource, but also to decrease the effects the urchin is having on the kelp forests. We have to make sure that ecosystem function still happens.”

CSIRO scientists study changes in important habitat types after record-high temperatures in the Torres Strait in 2016

But while markets for some new species are opening up, other species, such as the Jackass Morwong, are dwindling. The Jackass Morwong is an important species for commercial and recreational fisheries in southern Australia and has been fished by Indigenous groups such as the Camaraigal for generations. Morwong is also one of the most highly connected species in the southeast Australian ecosystem according to CSIRO’s scientific data, based on its feeding and habitat-mediated connections with other species.

“There does seem to be a pretty clear indication that the success of Jackass Morwong recruitment, (the number of larvae and juveniles surviving) has changed through time. That’s what we call a productivity change.”

Managers have had ongoing concerns around the sustainability of Jackass Morwong species and several other at-risk species. The Australian Fisheries Management Authority has commenced consultation with industry on options for spatial closures to ensure fishing mortality of at-risk species is substantially reduced.

Rock lobsters feeling the heat in Torres Strait

Change is also happening for fishers of significant species in the Torres Strait.

2018 saw some of the lowest-ever catches of rock lobster in the Torres Strait.

“We’ve certainly been hearing from Traditional Owners about a lot of changes they’re observing,” Plaganyi said.

“Climate change is very real to the people on the ground – Islanders are very in tune with how the environment operates.

“In 2018 we had the lowest-ever catches of tropical rock lobster in the region and we had to close the fishery early to protect its long-term sustainability. This had a major socio-economic impact for the Traditional Owners, because it’s the most important resource in the area. A lot of people depend on it economically.”

Eva and her fellow scientists tracked the reduced productivity to larger environmental changes, like the 2015-2016 El Niño.

“In the case of the rock lobster, we think that affected recruitment in the years that followed, which was then picked up in the numbers of animals caught in 2018, " Plaganyi said.

"Simultaneously, fishers were noticing a troubling increase in the number of lobsters dying in holding cages after being caught for live export.

“That was because in March 2016, we experienced record-high temperatures in the Torres Strait. This meant that the temperatures of the seawater in the holding cages was really high, and the oxygen levels in those cages was low. Fortunately the stock has since recovered.”

Another tool that CSIRO scientists have created to address these changes, is an evidence-based handbook that helps fisheries in the south-east of Australia ensure sustainable seafood stocks. The Adaptation of fisheries management to climate change handbook facilitates the design and evaluation of management systems for adjusting to environmental change and considers other aspects of fisheries management such as operations, infrastructure and safety.

This research received funding from the Australian Fisheries Management Authority and the Fisheries Research and Development Corporation.

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