Supporting a more sustainable aquaculture industry in Tasmania

By Carla Howarth 16 May 2023 5 min read

There's a body of water in Tasmania that has the potential to change the game for sustainable aquaculture.

Storm Bay, in the south-eastern region of Tasmania, is bounded by the Tasman Peninsula and Bruny Island.It's a large and deep bay, measuring 26km long and 40km wide, and extends south-eastward to the shelf-edge, where it connects to the Tasman Sea. It's also an area of interest for the further development of offshore salmon farms. The Fisheries Research and Development Corporation (FRDC) has funded a suite of research projects aiming to provide scientific knowledge and tools to guide sustainable management of the impacts from salmon farming within Storm Bay. One of the research projects, which has co-investment and is led by us, is the Storm Bay Biochemical Modelling and Information System.

The Storm Bay Biochemical Modelling and Information System project began in July 2018. It builds an information system that provides water quality observations and model results to support the sustainable management of aquaculture by the Tasmanian Government and salmon industry. The model can accurately simulate local currents and water circulation, nutrient cycling, plankton and dissolved oxygen. The model was calibrated using observations made available to the project from a number of sources, including the Integrated Marine Observing System, the Tasmanian Environmental Protection Authority Broadscale Environmental Monitoring Program, the Institute of Marine and Antarctic Studies, and us. Our researchers used new continuous data collected from moored water quality sensors in Storm Bay. They also used autonomous underwater vehicles to collect water quality observations throughout Storm Bay and in the open ocean, including one trip from Macquarie Harbour on the west coast of Tasmania.

Principal Research Scientist Dr Karen Wild-Allen said the research brought together around 25 experts in marine modelling and observations, plus technical experts. "The project aims to understand drivers of water quality in Storm Bay and capture this knowledge in a numerical model validated against observations, which could be described as a ‘digital twin’ of the marine system," she said. "This sort of research is really important as it provides the scientific evidence for environmental regulators, so that they can use this information to make the best decisions at the time for how our coastal waters are managed."These decisions impact all current and future users of our coastal waters."Senior Research Scientist Dr Clothilde Langlais said the project was created to support the decision making around sustainable and environmentally responsible aquaculture in Tasmania. "This research is here to provide science-based information to stakeholders and managers, so they can take informed decisions," she said. "It is also here for the general public, so that they can access science-based facts and be well-informed when taking part in the public debate about blue economy development. "The tool could now be used to answer other questions for strategic management of loads or operations, for long-term planning (climate change) or short-term responses to events (marine heat waves)." The project also has the potential for future expansion to multiple sub-regions around Tasmania and Australia, thereby facilitating the sustainable management of aquaculture across a wider geographic area.

Storm Bay is naturally mostly oligotrophic, meaning it's low in nutrients and has generally clear water, with areas of seagrass and macroalgae reefs. Dr Wild-Allen said the report found the majority of nutrients enter Storm Bay from offshore marine waters and the timing and delivery of these nutrients are modulated by ocean boundary currents. "In winter, the nutrient poor Zeehan Current travels south along the west coast of Tasmania and eastward past Storm Bay; this delays the winter influx of nutrient rich sub-Antarctic water until the Zeehan Current relaxes," she said. "In summer, the East Australia Current travels south along the east coast of Tasmania as a series of mesoscale eddies, as these eddies pass southeast Tasmania, deep water intrusions of nutrient rich water can enter Storm Bay. As boundary currents vary from year to year, the offshore nutrient supply to Storm Bay has considerable interannual variability."Simulated future scenarios with increased fish farms in Storm Bay predicted changes in water quality that were small, relative to natural interannual variation in nutrient supply to the system. They would be very difficult to detect with a monthly monitoring program, although continuous sensors may more readily identify systematic change."

Dr Wild-Allen said more leases would mean more nutrients sources for Storm Bay. "The scenario simulations that explored future management of Storm Bay with additional fish farm leases suggest an increase in ambient nutrient, phytoplankton chlorophyll, and turbidity concentrations. Also, a small decrease in bottom water oxygen and propagation of light to benthic habitat," she said. "A future scenario based on 2020 anthropogenic loads, plus an additional 3 kilotons of fish farm waste in Storm Bay, shows an increase in the area classified as mesotrophic (medium nutrient, annual mean chlorophyll between 1-3 mg m-3) from 34 per cent in a pre-Storm Bay development scenario to 42 per cent in this post-Storm Bay development scenario. As well as a corresponding 8 per cent reduction in oligotrophic area." Dr Wild-Allen said the research could now be used to inform science-based management of coastal water quality, explore possible futures with additional model scenarios, inform emergency response to an event, interpret sparse monitoring data and provide context for other scientific studies in the region. The Storm Bay Biochemical Modelling and Information System project has delivered its final report to the Department of Natural Resources and Environment Tasmania, the Environment Protection Authority Tasmania, and the FRDC. Simulated circulation, water quality and analysis products from the new model are available on the Storm Bay Modelling and Information Dashboard.The project final report is available on the FRDC website.