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By Dyani Lewis and Catherine Norwood 21 October 2020 5 min read

Prawn fisheries rely on healthy prawn-producing habitats, such as seagrass meadows (Image: Peter Southwood)

For prawn fishers in Wallis Lake, on the New South Wales coast north of Newcastle, the estuary and adjacent catchment are important natural assets that support the continued health of their fishery.

A new study is looking at the prawn-producing habitat in the estuary – made up of saltmarsh, seagrasses and mangroves – with a view to understanding how this natural capital supports the fishery’s productivity and to value its contribution through the use of natural capital accounting.

It is a process that also helps identify opportunities to add value and to assess threats to the health of ecosystem assets.

Research led by CSIRO and supported by the FRDC has demonstrated how natural capital accounting can be applied in fisheries. Stakeholders can now determine if it could improve management decisions and boost productivity, not only in the prawn fishery but also in all Australian primary industries.

The research has been applied to three case studies, including Wallis Lake, prepared as part of a larger national project, ‘Increasing farm gate profits: the role of natural capital accounts’, funded through the Department of Agriculture, Water and the Environment’s Rural R&D for Profit program. Other case studies are being prepared for cotton growers and the forestry sector.

Creating the accounts

Environmental scientist Becky Schmidt at CSIRO has led the Wallis Lake prawn fisheries case study. She says the methodology CSIRO has developed draws on the business-focused Natural Capital Protocol and the UN’s System of Environmental–Economic Accounting[Link will open in a new window], to determine the connections between ecosystem assets, society and the economy.

The research team consisted of Becky Schmidt and Ian Cresswell from CSIRO, University of Newcastle fishery experts Vincent Raoult and Troy Gaston, and Matt Taylor at the NSW Department of Primary Industries.

Becky Schmidt says people often do not know where to start when assessing their natural capital: “They don’t know what to measure, how to measure it and what is critical.”

To identify these factors, the research team consulted with many stakeholders who have an interest in the health and productivity of Wallis Lake, including commercial and recreational fishers, land managers, local and state governments, and local conservation groups. It also consulted with the broader NSW fishing industry.

The Wallis Lake estuary supports a moderate-sized prawn fishery that can produce up to 60 tonnes of prawns a year, mostly in the summer months. More than 20 fishing businesses can be involved in the annual harvest and prawns are also a popular catch for recreational fishers.

The Wallis Lake estuary has important habitats including seagrass beds, mangroves and saltmarshes. Eastern School Prawn (Metapenaeus macleayi) is the most commonly caught prawn in the estuary, and the habitat supports it through several stages of its life cycle.

Prawn fisheries also rely on mangroves. (Image: Rebecca49)

Identifying what matters

Key natural assets for the continued operation of prawn fishing in Wallis Lake were identified as estuarine waters suitable for prawns, prawn-producing habitat, biodiversity and a renewable prawn population.

The researchers and stakeholders identified three high-priority activities or events that have the potential to impact these assets: pulses of fresh water into the estuary, agricultural activity in the catchment, and commercial fishing in the estuary.

Wallis Lake is fed by several small rivers that drain a catchment of 1200 square kilometres of mostly agricultural land. While fresh water inputs are important to Eastern School Prawn, during heavy or sustained downpours, run-off from adjacent farmland can cause water quality to decline. The knock-on effects can include widespread die-off of seagrasses, which are vital prawn habitat and essential for good water quality.

Other catchment-based activities, such as land clearing and trampling of saltmarsh by livestock, can also adversely affect water quality and the health of the estuarine ecosystems.

The project shows effective management of the whole system requires catchment and water management alongside fisheries management, so the direct impacts of both terrestrial and water-based users on the shared natural capital in the estuary can be considered.

In consultation with stakeholders, the researchers proposed seven natural capital accounts that could be compiled from publicly available data, and which reflect key ecosystem assets:

  • precipitation in the catchment;
  • fresh water pulses in the catchment;
  • land use in the catchment;
  • terrestrial and riparian vegetation in the catchment;
  • aquatic prawn habitat;
  • water quality in the prawn habitat; and
  • landed-prawn biomass.

Taken together, such accounts form a picture of the overall health of the ecosystem upon which prawns depend. Compiling these accounts, with repeatable measurements added over time, is expected to provide a better understanding of the main drivers of estuary health and the prawn-fishing industry.

Industry benefits

A bird’s-eye view of estuary health is not the only way fishers stand to benefit from the research. Commercial fishers who assess their operation through a rigorous natural capital accounting process could be better placed to convince investors of their business’s long-term viability.

Or they could use the process to gain social licence by demonstrating to the community they are good managers of the estuary. Also, truly understanding the threats to critical natural assets and business risks gives fishers the chance to adjust their goals to recognise a changing outlook.

“Under a changing climate, we’re increasingly aware resources are finite and under threat,” says Becky Schmidt. “So, we need to be more efficient in our use of resources and also ensure the natural system has what it needs to function going into the future.”

She says natural capital accounting has highlighted gaps in available data that indicate opportunities to improve monitoring, for example, of fresh water pulses into the estuary.

The Wallis Lake case study identified small-scale fishery enterprises are generally too small to invest heavily in scientific data collection and maintain their own set of natural capital accounts. In contrast to land-based enterprises, which usually fully control their land, fishers are not the only estuary users; a diverse range of people use them and impact them, either directly or through impacts on their associated catchments.

But the fishers could band together, working with larger organisations such as local government or catchment agencies to gather the data required to monitor and improve management of their shared resource.

Brian Hughes, the estuary and marine officer for Hunter Local Land Services, says local councils and producers do not always work closely together. “This could really help by strengthening links between the two.”

While the Wallis Lake natural capital accounts focus on local conditions, similar methods can be applied to other estuaries and fisheries, and to regional areas more broadly.

“We are trialling a new method here which we hope will add value to fisheries right across Australia,” says Becky Schmidt.

The final reports, Designing natural capital accounts for the prawn-fishing industry and Experimental natural capital accounts for the prawn-fishing industry in the Wallis Lake estuary, are expected to be published later this year.

This article was originally published on the Fisheries Research and Development Corporation website[Link will open in a new window].

Mangrove flower (Image: Malcom Tattersall)

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