The final report of the Huon Estuary study, the result of a three-year investigation by CSIRO Marine Research, also calls for an environmental monitoring strategy to guide long-term use of Tasmania’s Huon Estuary.

A key finding of the report is that the Huon Estuary is a ‘substantially natural’ waterway that has not changed dramatically from its historic baseline. In general, its environmental quality was found to be high and that of its two main source waters – the Huon river, and the D’Entrecasteaux channel coastal waters of southeast Tasmania – is very high. Land-based activities appear to have exerted only localised effects on the estuary’s environmental quality.

Funded by CSIRO, the Fisheries Research and Development Corporation and marine farming interests Tassal and Huon Aquaculture, the study provides new standards for maintaining the environmental health of Tasmania’s $120 million a year Atlantic salmon farming industry, based in the highly-productive river estuary.

The Huon River and its estuary in southeastern Tasmania have supported forestry and horticulture since early in the region’s settlement. The Huon valley community is now developing a broader economy based on the emerging industries of tourism and aquaculture. Comprehensive and effective management of the catchment and waterways are fundamental to a prosperous future that is in harmony with the natural ecosystem.

“Water quality is undoubtedly the primary issue governing growth in Australia’s $600 million aquaculture industry,” says Peter Dundas-Smith, the executive director of the Fisheries Research and Development Corporation.

Dr Ed Butler, CSIRO’s project leader, says marine farming is only one of the many human activities putting pressure on coastal ecosystems and it should not be the focus of undue or unfair attention.

“A whole-of-estuary approach is needed that recognises all of the major natural and human influences,” Dr Butler said. In recognition of the complexity of the ecosystem involved, the study took an interdisciplinary approach that combined expertise in physics, chemistry and biology, and considered the critical time and space scales.

This meant the fish farming industry could be studied in the context of the entire estuary, and beyond to the catchment where appropriate. This reflects current thinking, which recognises that estuaries and other coastal water bodies are best managed when governed on a catchment scale.

Dr Butler added: “The report should be of interest to communities elsewhere in Australia who want to introduce or expand aquacultural production and ensure a positive environmental legacy for the benefit of future generations.”

Industry and community groups have welcomed the report’s conclusions as an important foundation for future multiple-use management of competing recreational, industrial, and environmental needs.

The chairman of the Tasmanian Salmonid Growers Association, Peter Bender, whose company, Huon Aquaculture, was a key participant in the study, says the report is vital to the fish farming industry, which relies on waters of the highest environmental quality.

“Importantly, this accords with the Huon community’s interest in fostering industries that are significant economic contributors while maintaining the necessary environmental balance.

“The report will be extremely valuable to the industry, as it will guide us in the best ways of managing sustainable growth. With new technologies and appropriate farming techniques, growth and responsible environmental management can go hand in hand.”

The goals of the study were:

  • To determine the sources, distribution and cycling of nutrients (including those from finfish farming) in the Huon River estuary, and relate nutrients and physical parameters to algal dynamics.
  • To evaluate the processes (and their rates) that contribute organic matter to sediments from finfish farming and natural sources; and the significance of this organic matter in the cycling of nutrients through the sediments.
  • To determine the sedimentary distribution of organic matter around the fish cages that ensues from salmonid farm operation, and the time needed for degraded sediments to return to ambient conditions when cages are removed (the latter is a pilot experiment).
  • To test the usefulness of different methods for monitoring the environmental quality of sediments and the water column.

    While finding the estuarine quality generally high, the report highlighted three issues requiring further attention by managers. The first was the degraded quality of some lower catchment streams, apparently as a result of land-based activities in their subcatchment. Until now, the effects remain localised.

    The second issue is oxygen depletion in deeper holes in the upper estuary, which may have natural causes, but the researchers also observed a few instances of very low concentrations in bottom waters in the lower estuary in summer.

    The final issue of concern was the appearance of raised levels of ammonia and nitrite (readily available forms of nitrogen for microalgae) in bottom waters in the lower estuary after dense microalgal blooms. In combination with oxygen depletion, these increased nutrient concentrations indicate that sediments are recycling and releasing nutrients efficiently back to the water column, making the estuary more vulnerable to increases in nutrient loads.

    The report further recommended that a formal risk assessment of the system’s carrying capacity should be carried out to underpin any further expansion of finfish farming in the Huon Estuary.

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