As a scientist, with over 35 years’ experience in water quality management, I am very concerned about the expansion of salmon aquaculture in Storm Bay for the reasons outlined below.
Scale and rate of development
The planned expansion of salmon aquaculture in Storm Bay at 40,000 to 80,000 tonnes/year will more than double production for the entire state (currently at about 55,000 tonnes).
This comes with a very large nutrient load, estimated at 2300 to 4600 tonnes/year of bioavailable nitrogen. To put it in perspective, this is 6 to 12 times the current nutrient load from all sewage treatment plants in the city of Hobart or 2 to 4 times the estimated load for all sewage generated in Tasmania.
Risks associated with nutrient overload
Too many nutrients are known to cause a whole cascade of problems, including run-away algal blooms, damage, and loss of reef and seagrass communities, low oxygen levels, fish kills and rotting algae on beaches. In the Derwent estuary, this is further compounded by heavy metal contamination. Studies have shown that when oxygen levels drop, heavy metals are released from contaminated sediments, and mercury can be converted to more toxic forms. Storm Bay sets the overall water quality for the Derwent, which is already nutrient-stressed. Over 100 million dollars has been spent in recent years to reduce nutrient loads to the Derwent from sewage treatment plants – will this now be canceled out by salmon production in Storm Bay?
Beyond the Derwent, Storm Bay has a wealth and diversity of natural systems that support recreational and commercial fishing, tourism, and a number of protected and endangered species. The shallow, sheltered bays, fringing reefs and seagrass meadows of Norfolk and Frederick Henry bays are particularly vulnerable to nutrient damage.
Lack of robust scientific understanding is a major problem. Our understanding of the Storm Bay system is not yet well developed, and we have no idea of what the carrying capacity of Storm Bay may be. In particular:
• Valuable habitats and sensitive areas have not been clearly identified or mapped
• Baseline monitoring has not been completed, particularly for reefs and seagrass meadows
• A whole-of Storm Bay monitoring program has not yet been established
• Work on predictive models is just beginning and will take several years to complete
• Public reporting is limited and community consultation lacks transparency.
‘Adaptive management’ vs the precautionary principle
The regulators and proponents are working on the assumption that Storm Bay can absorb a massive nutrient load, and that risks can be addressed using ‘adaptive management’ – which seems to be interpreted as dealing with any problems if and when they arise. This is simply not credible, as has been demonstrated via the Macquarie Harbour debacle. The production cycle from smolt to harvest is too long, and the value of the product is too high; no one is going to pull the plug halfway through.
Adaptive management is not a substitute for careful planning. To be successful, adaptive management first requires good system understanding, including comprehensive baseline surveys. This should then be coupled with predictive models that have been validated, and which can be used to estimate the system’s carrying capacity. As production levels increase, a detailed monitoring program must confirm that the system can cope with the inputs as predicted and that the models are accurate. This information needs to be shared with the community in a timely fashion, so they have confidence in the process. And finally– and most importantly – adaptive management must set the criteria, triggers and management response for when things go wrong. This cannot be done on an ad hoc basis.
In summary, this major expansion needs to be based on robust science, which is still several years away. In the meantime, the precautionary principle should prevail, and further expansion should be halted until the necessary monitoring, modelling and management controls are in place.
Christine Coughanowr
Christine Coughanowr (BSc, MSc) is an independent scientist with over 35 years’ experience in water quality science and management. She was the founder and director of the Derwent Estuary Program for 25 years, has worked internationally as a consultant, and is a Churchill Fellow.