Fish Farming Environmental Report (EW)
Thursday, February 16, 2012 at 4:54PM
Bill Barclay

The Report on the Potential Environmental Effects of Fish Farming was presented to EW Environment Committee on 25 January.

This report is critically important at this stage of the development of the proposed finfish industry in Wilson’s Bay and beyond. It contains warnings of the likely effects in a number of areas – some of which I raised in an earlier post (Hauraki Gulf, dated 1 November 2011), but which are starkly outlined in detail in this Report.

The areas covered include the inputs of feed, and drugs & chemicals, then the effects on waves and currents, wild fish, diseases and parasites, biofouling and invasive species, seafloor, water quality, marine mammals and birds. Please go directly to the URL above for the full report. I have included in this post extracts only of what I consider the most important aspects, but these are out of context and therefore should be read read advisedly. They nevertheless provide an outline of some very disturbing information about the known possible/likely consequences of proceeding with fish farming in our delicate Gulf environment.

What is staggering is the final conclusion reached in the Report that  states :

“We are confident that the RMA consent process will allow Council to manage the environmental effects and intervene promptly and effectively in case environmental effects become unacceptable”.

I can see no reason whatsoever why these EW scientists exibit such confidence in their ability, together with the RMA, to satisfactorily manage the risks posed by this development. The Hauraki Gulf is just too precious to allow the enthusiasm for this industry to override common sense. This contradicts earlier statements that I have made regarding this industry, but on reviewing all the evidence – particularly that contained in this Report, I believe that the risks are just too great without far greater depth of research in regard to mitigation. 

I should say that the content of this Report almost mirrors the content of a similar report prepared by the Department of Primary Industry in Darwin prior to the commencement of a substantial Barramundi fish farming enterprise on Bathurst Island in 2002. It failed five years later for a myriad of reasons, most of which are forewarned in this Report. I was there at the time, read the Report, watched the industry grow, and collapse, and observed the severe environmental effects this entailed.    

Here are the Extracts :


“If poorly managed fish farming can have significant environmental effects. Council will manage these through the Regional Coastal Plan (“the Plan”) and consent process. The amended Plan includes a clear and robust set of information requirements and decision making criteria that will result in the consent being declined if the applicant cannot demonstrate its sustainability

A summary table lists the spatial scale, recovery time and severity of the effect(s). The severity of effects was firstly assessed in the absence of any management intervention (“Potential effects”). Secondly, the level of management interventions enforceable under the RMA (and therefore under the control of Council) were assessed (“Management intervention”). Thirdly, the severity of the net effects was assessed, i.e. assuming that those management methods under the control of Council are implemented (“Net effects


Fish aquaculture still consumes more animal protein than it produces as harvestable product. For example, it is estimated that 2-5 kg of wild fish are required to produce a single kilogram of farmed salmon4. Fish meal and fish oil are the preferred protein source and make up 15 to 40 percent of most aquaculture feeds.

Drugs and Chemicals

Because of the high density at which fish are held, the use of drugs and chemicals is generally necessary in cage aquaculture. Drugs used include vaccines, antibiotics and treatments for parasites and fungal infections. In addition, herbicides and antifoulants (most commonly based on copper-compounds) are often used on cages to prevent the build-up of fouling organisms and disinfectants are used to clean farm equipment.

Waves & Currents

Fish farm structures present an obstacle to flow and therefore will affect the local wave and current regime. Many processes in the marine environment are driven by water flow. As a consequence of a modified wave and current regime, local deposition of fine sediments or other particles released from fish cages may increase or, alternatively, scouring of the seabed may result in a coarsening of sediments. In addition, the dispersal of particles or cages may be modified.

Wild Fish

Fish invariably escape from sea cages, for example through seal or shark attacks, tearing cages, or storms causing the breakdown of pontoons or cage structures. The environmental impacts of escaped fish include genetic effects on local wild fish populations. The environmental impacts of escapees can be prevented by preventing fish from escaping, but in practice this is hard to achieve for cage culture.

Diseases & Parasites

Kingfish in Australasia have a range of known pathogens and parasites, but it is apparent that the monogenean (flatworm) ecto-parasites are the most problematic in Australian kingfish culture. Monogeneans have direct, single-host life-cycles (i.e. do not require an intermediate host) and can multiply rapidly in high-density aquaculture environments. Furthermore, their eggs become entangled in fish nets and fouling, leading to high reinfection rates of cultured fish. Hutson et al. (2007) undertook a risk assessment for metazoan parasites of kingfish in South Australia sea-cage culture, and identified the monogeneans Benedenia seriolae and Zeuxapta seriolae as “extremely likely to establish and proliferate” at new farm sites. Benedenia seriolae (skin fluke) inhabits the skin and fins of kingfish, and can negatively impact fish growth and marketability. The cost of managing monogenean parasites such as Benedenia seriolae and Zeuxapta seriolae is seen as a significant barrier to the expansion of kingfish farming in Australia (Hutson et al. 2007b) and potentially New Zealand (Leef & Lee 2009), with estimates of 20% of total production costs to control these parasites cited in the literature (e.g. Ernst et al. 2005)

Biofouling and Invasive Species

There is a well established link between aquaculture and the spread of native biofouling organisms and invasive species. Farm structures provide ideal habitat for their growth, and the movement of vessels, equipment and stock provide a vector for their dispersal. High dissolved nutrient loads may also promote the growth of unwanted algae. The long-term effects of invasive species on native marine species and habitats could be significant. Removal of marine farms infested by invasive species may eliminate a significant reservoir, but the broader effects of invasive species will probably be ongoing.


The deposition of farm waste results in organic enrichment of the seafloor due to the high organic content of the deposited material. The microbial decay of the waste material can dramatically alter the chemistry and ecology of the seafloor. As a consequence, impacts resulting from the deposition of farm waste are likely to include: reduced abundance and diversity of sediment-dwelling animals, oxygen-depleted sediments (anoxic sediments), nutrient (nitrogen and phosphorous) release from the sediment, hydrogen sulphide production and, in extreme cases, the growth of mat-forming sulphide oxidising bacteria such as Beggiatoa sp.

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. Dissolved waste from cage culture includes ammonia, phosphorus and dissolved organic waste, which is rich in nitrogen and phosphorus. Oils from the diet may form a film on the water surface in the vicinity of the cages.

A modelling study of the cumulative effects of fish farms in the Wilson Bay MarineFarming Zone and the Coromandel Marine Farming Zone indicated that increases in nitrogen are mainly confined to areas near the two fish farming sites. However, the study suggests that enhanced growth of phytoplankton will occur over large areas and that the phytoplankton footprints13 of the two farms overlap. The modelled footprints extended through the entire Firth of Thames and southern Hauraki Gulf as well as along the Coromandel coastline north of Coromandel township.

It is important to remember, that cage aquaculture is not the only source of nutrients to coastal waters. If cage culture is situated in areas where there are already high nutrient inputs from the land (such as from sewage discharges and agricultural runoff), it could contribute to an overloading of nutrients to coastal waters


We are confident that the RMA consent process will allow Council to manage the environmental effects and intervene promptly and effectively in case environmental effects become unacceptable”.




Article originally appeared on BillBarcBlog (
See website for complete article licensing information.