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Published: 2012-02-09 00:00:00

Waikato Regional Council will manage and monitor possible effects of fish farming on the environment through consenting and tender processes.

These assurances meant the council’s policy and strategy committee could be confident about seeking expressions of interest for fish farming space, said committee chair Paula Southgate.

The committee yesterday backed a proposal to seek expressions of interest for fish farming space. This is a relatively informal process in which potential applicants submit a brief outline of the fish farming they might propose to do.

Through this process potential applicants will be identified, allowing the council to determine the level of demand for fish farming space and types of fish that might be farmed. Calling for tenders would follow.

Earlier this week, a report to the environment committee discussed 10 potential environmental effects of fish farming in the Firth of Thames and outlined possible management options and controls.
The effects were categorised into feed supply, the release of drugs and chemicals, waves and currents, wild fish, diseases and parasites, biofouling and invasive species, the seafloor, water quality, marine mammals and birds.

“The Government has made it clear aquaculture will go ahead in the region, but fish farming can have significant effects on the environment if not well managed,” said Cr Southgate.

"However, we have good information and through the Resource Management Act consent process and tendering criteria, we have the tools to manage the environmental effects and take swift action if necessary.

The council and the Ministry of Fisheries’ Aquaculture Unit commissioned studies assessing the potential effects and carrying capacities of fish farms. The work was done ahead of the recent central government reforms that saw the creation of two new fish farming zones amounting to approximately 400 ha of Waikato’s marine area.
The report to the committee draws on these assessments, saying the council will be able to manage potential effects through the Regional Coastal Plan which details the sustainability requirements that must be met before consents to farm can be granted, and also through the consenting and tendering processes.

Even before consent applications can be lodged, fish farming companies will need to demonstrate their track record on environmental systems and management as part of the competitive tender process for 80 per cent of the space within the two zones. The first 20 per cent of the area must be allocated to the Maori Trustee.

Following are three examples of the ten possible environmental effects of fish farming and steps which could be taken to mitigate them:

Water quality

 Water quality is affected by the direct release of dissolved nutrients from fish farms and the release of dissolved nutrients from deposited solid farm waste. Oils from feed may form a film on the water surface.
Where cages are situated in areas of medium to strong currents, nutrients get rapidly diluted and adverse effects can be mitigated.
The Firth of Thames is a nutrient rich environment and subject to increasing land based discharges. Initial estimates indicated that the nitrogen released from fish farms in Wilson Bay could constitute a significant proportion of the overall nitrogen budget for the Firth relative to river and ocean-derived inputs. As a consequence, a nitrogen limit has been imposed on fish farms in the Firth and Coromandel areas.
The nitrogen input might be partially offset by nitrogen removal through shellfish farming. The current scale of mussel farming in the Firth and Coromandel removes nitrogen equivalent to about 2900 tonnes of kingfish farming. Mussels remove nitrogen in the form of phytoplankton that they selectively graze on while fish add it in the form of dissolved nitrogen and organic matter which promotes phytoplankton growth downstream. However, there is uncertainty about the effectiveness of the offsetting effect.
Controls include locating fish farms in well-flushed areas, determining baseline levels of nutrients and phytoplankton, developing nutrient budgets, managing stocking and feeding rates to limit impact, developing standards and limits of acceptable change in water quality in consultation with industry, tangata whenua and the community.


Uneaten food and fish excrement could have significant impact on the seafloor. The microbial decay of waste produces can alter the chemistry and ecology of the seafloor resulting in reduced abundance and diversity of sediment-dwelling animals, oxygen depleted sediments, nutrient release from the sediment, hydrogen sulphide production, and in extreme cases the growth of mat-forming sulphide oxidising bacteria.
Although the impacts are unlikely to extend far beyond the farm footprint, recovery rates following the removal of fish farms could take up to 10 years.
Detailed information would need to be provided to demonstrate that the seafloor would be able to assimilate the organic matter deposited under the cages. Consent conditions will require comprehensive monitoring.

Drugs and chemicals

Drugs and chemicals are used, among others, to prevent and treat parasites and disease in farmed fish and have the potential to significantly affect the environment if not well-managed. Management options include the requirement for fish farmers to demonstrate compliance with New Zealand Food Standards Authority and Environmental Risk Management Authority regulations, monitoring concentrations of chemicals in the water column near farms, and minimising use of copper-based antifoulant paints through a code of practice. Controls available through the consent or tender processes include the need for a consent to use chemicals in fish farming, and associated monitoring and compliance with national standards.