OXYGEN LEVELS AND BIOLOGICAL COMMUNITIES – MACQUARIE HARBOUR

When Atlantic salmon farming in Macquarie Harbour expanded in the early 2010s, ongoing monitoring detected a deterioration in sediment conditions and a major decline in oxygen levels in bottom waters. This was much greater than initial modelling by external consultants had predicted.

To understand what was going on, the focus turned to understanding oxygen dynamics in the harbour and the role of salmon farming and other influences. This included industry, IMAS and CSIRO conducting real time environmental monitoring, IMAS carrying out ongoing benthic (bottom water) assessments, and CSIRO developing a water quality model.

This work played a crucial role in informing and driving management decisions on Atlantic salmon farming in Macquarie Harbour, and redefined the allowable cap for total production within the Harbour.

Since the cap was redefined, researchers have observed a recovery of benthic conditions throughout the system, with fauna seeming to migrate back into affected areas when oxygen levels increase. However, IMAS’s most recent report on environmental conditions in Macquarie Harbour show that the oxygen concentrations in midwater, which has the longest residence time, remain low.

Modelling work has also shown the intricate play of oxygen dynamics between the influences of seawater inundation from the Southern Ocean, river inputs from the Gordon and King Rivers, and the wind from prevailing weather conditions.

The research shows an intricate link between environmental conditions in Macquarie Harbour – particularly dissolved oxygen, salinity and temperature – and the ecology, movement and physiology of the Maugean skate.

IMAS research recently found that Macquarie Harbour is the last remaining habitat of the Maugean skate – a marine environment that is significantly impacted by human activity.

Although it is unclear how the population dynamics of the skate are affected by changes to the environmental conditions and other pressures in Macquarie Harbour, research published in May 2023 revealed that the Maugean Skate population has rapidly declined, with relative abundance dropping by almost half between 2014 and 2021 in Macquarie Harbour. It highlights that the environmental changes in the harbour have increased the skate’s vulnerability to sudden high-imapct events, such as water column turn-over driven by westerly winds or dramatic shifts in oxygen levels.

The urgency of managing the potential threats to this species is clear, as is the need for ongoing population monitoring to support future conservation action and ensure the survival of this unique and micro-endemic species.

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BROADSCALE BIOGEOCHEMICAL MODELLING AND MONITORING, HABITAT MAPPING AND DECISION SUPPORT TOOLS – STORM BAY

The Storm Bay Research Program is a suite of FRDC research projects that will provide scientific knowledge and tools to inform the management of Atlantic salmon farming within Storm Bay. The four priority research projects are:

  1. The IMAS-led Storm Bay Observing System project is tasked with developing and implementing an environmental monitoring program that assesses the interaction between the environment and farming operations at both local and system wide scales. This work will map and monitor a range of habitat types throughout Storm Bay, including water column, soft sediments, inshore and deep reefs and seagrass habitats. It will provide a robust understanding of these habitats to ensure the industry’s environmental footprint is well understood, and future monitoring will capture any habitat changes or impacts.
  2. The CSIRO Storm Bay Modelling and Information System project has built an information system that delivers water quality observations and biogeochemical model results, to inform the sustainable development and management of Atlantic salmon farming in Storm Bay. It involves developing a 3D model simulating hydrodynamics, sediment and biogeochemical dynamics, that evaluates water quality and nutrients to estimate the ecosystem’s capacity to assimilate Atlantic salmon-related nutrient inputs. The model is validated against observations from satellites, moorings, autonomous gliders, benthic landers, and in-situ monitoring programs to ensure it is sufficiently accurate. Model simulations give researchers the ability to understand current environmental conditions and forecast the environmental response under alternative management.
  3. The CSIRO Decision Support Tools project is delivering systems and knowledge for ongoing science-based resource management in Storm Bay. It aims to provide key stakeholders with access to practical tools and capabilities, to support decision making on environmental aspects of aquaculture operations. These tools include a visualisation system to display and deliver model results, a re-locatable downscaling model and an assessment tool to rapidly estimate the water quality impacts of changing Atlantic salmon loads.
  4. The Governance and Communication support project will coordinate and support project governance and communication outputs of these three projects.