Former EPA head shreds credibility of regulator and salmon industry

Advice ignored, now ecosystem faces collapse - early modelling of the salmon industry's impact on Macquarie Harbour was fraught, writes Alex Schapp, former director of the Tasmanian EPA (The Mercury (paywalled) 14 February 2024).

I was first involved with Tasmania's salmon farming industry in the 1980s when, as a research officer for the Department of Sea Fisheries, I undertook environmental monitoring and assessment dives under salmon farms, then later as director of Marine Resources (which included oversight of management of marine farming), and most recently as director of the EPA until 2016, when I retired.

The salmon industry's recent announcement of modelling of salmon farming's contribution to oxygen depletion in Macquarie Harbour brings to mind the modelling that the industry commissioned to support the major expansion of farming in the harbour.

At that time I was the director of the EPA and therefore a member of the Marine Farm Planning Review Panel which was to advise the minister of the merits of any proposed new Marine Farm Development Plan for Macquarie Harbour.

The industry had commissioned reputable consultants to conduct the modelling of how salmon farming nutrient inputs would likely impact the unique and poorly understood environment of Macquarie Harbour. The panel raised concerns with the consultants that there was already evidence from EPA monitoring data and industry participants that the existing low intensity farming was already raising nutrient levels in what had been a low nutrient environment.

That evidence included elevated nitrogen levels, including in the salt wedge at its furthest limit several kilometres up the Gordon River, and elevated ammonia levels well inside the bounds of the World Heritage Area.

The final Environmental Impact Assessment Report based on the modelling did not address these concerns adequately. Indeed, the panel was so concerned about the matter that it advised the minister that we felt the report was premised upon a range of assumptions about important nutrient and water flow parameters which were unreasonably optimistic even in their most pessimistic scenarios. We advised that it was very likely that the harbour would not be able to deal with significant additional nutrient loading and was perhaps already very close to the maximum loading. We further advised that the siting of the proposed zones was generally appropriate and that an adaptive management approach would be appropriate for the stocking of those zones with salmon.

Given the uncertainty and the risk of serious harm, we advised that the adaptive management approach should involve a slow rate of expansion with frequent monitoring and real time reporting so that any adverse impacts could be detected early to allow for corrective action before they became too severe.

Instead, the industry was allowed to expand as quickly as it could, much to the dismay of those industry participants who were not expanding so quickly. The fears of those participants and the panel were realised with the sudden catastrophic collapse of oxygen levels in the harbour. This unique ecosystem now featured large expanses where there was insufficient oxygen for fish and many other organisms to survive.

None of the modelling projections predicted such an outcome because the models were driven by unreasonably optimistic assumptions. Despite the improved understanding of Macquarie Harbour dynamics a decade later, there remains considerable uncertainty about how this unique ecosystem operates, and so any modelling remains vulnerable to the quality of its input parameter estimates. It is true that the geomorphology of the harbour, altered flow regime of the Gordon River and dependence on episodic weather events leaves the harbour vulnerable to low oxygen levels because of poor flushing. It is also true that the harbour still suffers the effects of many years of mine discharge. The evidence to date though is very clear that it is the nutrient input and consequent biological oxygen demand caused by the salmon industry that has pushed the system over the edge into catastrophic collapse.

It is important to heed this history because such mistakes must not be made again. It is all too easy for politicians and public servants to succumb to the unceasing pressures exerted by industry when it presents a seemingly plausible excuse not to apply the laws of the land as the evidence demands.

The regulator should quite rightly consider what alternative factors may be contributing to the situation in Macquarie Harbour. However, it must not blithely accept the assertions of industry: "it was them what done it guv, it wasn't us and you can't prove it was us." Any such assertion and any evidence presented to support it must be very carefully scrutinised and, when the environmental consequences of a mistake are so enormous, a truly precautionary approach is required by law.

• Alex Schapp is a former director of the Tasmanian EPA and has worked in environmental monitoring of the aquaculture industry.