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Technical report

Environmental research in Macquarie harbour

8 Feb 2017

The attached Institute of Marine and Antarctic Studies (IMAS) Technical Report, Environmental Research in Macquarie Harbour- Interim Synopsis of Benthic and Water Column Conditions January 2017, was prepared by Dr Ross and Associate Professor MacLeod at the EPA Director’s request in November 2016.

The three salmon companies were advised that this report would be made publically available as the earliest opportunity once it had been finalised and cleared by the University or Tasmania.

Since the late 1980’s the Macquarie Harbour has been a site for caged finfish (salmon and trout) aquaculture. Production has steadily increased over the years reaching 9,000 tonnes in 2011. In 2012 an expansion lease area was approved and subsequent stocking from 2013 has seen a further increase in production, with production approaching 16,000 tonnes in 2015. In March 2016, the allowable cap for production was 21, 500 tonnes, to be reviewed in early 2017.

In late 2013 a decline in DO levels in the bottom waters of the Harbour was confirmed. To investigate this issue the Tasmanian Salmonid Growers Association (TSGA) established the Macquarie Harbour Dissolved Oxygen Working Group (MHDOWG). Since then studies have investigated Harbour oxygen dynamics, with an emphasis of identifying the drivers of oxygen resupply and consumption to help determine attribution for the observed decline (MHDOWG 2014, Revill et al.2015, Ross et al. 2016; Maxey et al. 2016). In mid-2014 there was a significant recharge of bottom waters, but oxygen levels have since declined back to very low levels.

In light of the recent benthic observations and return to very low DO levels in bottom waters, the Environment Protection Authority (EPA) and Department of Primary Industries, Parks, Water and Environment (DPIPWE) have requested IMAS provide an interim synopsis of the science and current status of the benthic and water column environments.

In the first part of the synopsis we provide a brief summary of the key research projects and their findings with a focus on the ecology and condition of the Harbour benthic and water column environments. This provides important context for the subsequent presentation and discussion of the latest observations and current status of the Macquarie Harbour environment. We finish with a discussion of suggested research priorities aimed at improving our understanding of the current situation that will assist management in the short to long term.

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