Mitigation and best practice options

Some simple steps to minimise the effects of aquaculture activities on water quality and mahinga kai.

Some simple steps to minimise the effects of aquaculture activities on water quality and mahinga kai.

Shellfish farms

Reduce the effects of nutrients from aquaculture

Adverse water quality effects from oyster farming are more likely where farms are overstocked and sited in poorly flushed environments. This can be avoided by appropriate site selection, and by ensuring farm structures have a minimal effect on flushing processes.

Assess the environmental impacts of multiple aquaculture farms

Shellfish farms are generally situated over muddy habitats that are naturally adapted to high rates of deposition to minimise habitat modification and protect the biodiversity of more sensitive habitat types. If there is more than one existing farm in a bay, applications for new farms will often be required to investigate the cumulative effects of further shellfish farms on the marine environment. Seek professional advice.

Fish farms

Reduce the effects of nutrients from aquaculture

Much of the potential for impacts from fish farms arises from faeces and excess food that can build up beneath the floating cages. These problems can be minimised by locating fish farms in deeper, well-flushed areas and through farm management practices that use appropriate cage design and orientation to ensure minimal obstruction of water currents, control stocking densities and limit food wastage.

Select a site suitable for fish farming activities

In Aotearoa, it is usual to site salmon farms over muddy habitats that are adapted to naturally higher rates of deposition. This minimises habitat modification and protects biodiversity of more sensitive habitats. Also, the low stocking densities and the lack of disease in Aotearoa means that farmers do not need the antibiotics and chemicals that are often used in salmon farms elsewhere.

Careful management of aquaculture practices, such as site location, stocking densities, line orientation, and harvesting techniques can be used to minimise the impacts on the environment.

Customary fishing and harvesting

Priority should be placed on catchment management to mitigate the specific impacts of the surrounding land use or industry discharges. This can greatly reduce inputs of nutrients, sediments, chemical contaminants, and pathogens into waterways. In particular, direct discharges containing contaminants and pathogens into waterways should be eliminated.

Nutrients - reduce inputs of nitrogen and phosphorus into waterways from surrounding land use activities.

Water quality - improve stream/river water quality to improve inner harbor water quality, as the two are intimately connected.

Riparian planting - fence waterways to prevent stock access to stream banks, and create and maintain a vegetated riparian buffer that can greatly reduce the damaging effects of sediment and nutrients.

Temporary prevention measures

Ensure warnings are issued after significant sewage spills for a adequate period of time. It is advisable not to collect shellfish near urban areas because of the ongoing impacts of stormwater and sewage-related contamination.