A fishy tale…

| April 29, 2021
Why is it left to actors, writers and pop stars to focus public attention on the environment? It’s bad enough putting up with the predictions of economists about the climate. Now it appears that celebrity is becoming a pre-requisite for scientific credibility.
Author Richard Flanagan would probably object to my characterising him in this way. However, he has described salmon farms in Tasmanian offshore waters as “massive floating feedlots”. Many, including myself, working on pollution control decades ago, sounded the same warning as Mr Flanagan, but the Tasmanian authorities chose to adopt crude and deceptive standards for nutrient loads from salmon farms.
The World Wildlife Fund (WWF) guided a major salmon producer’s ‘sustainability’ practices. The WWF logo appeared beside that of the company and presumably this arrangement entails support for WWF activities elsewhere. But does that alliance guarantee best practice environmental management?
Consumers of farmed salmon have been encouraged to believe that the product is not harmful to the environment. As in other industries, waste treatment adds to the cost of production and profitability will be improved if the cost of waste management can be externalised. In this case, a trade-off of this kind would amount to cheaper salmon at the expense of marine ecosystems.
Fish wastes and feed residues contain substances that are rich in nitrogen, like fertilisers. This enrichment causes nuisance weed and algae growth, among other detrimental effects. Mr Flanagan alleges that the pollution load is equivalent to untreated sewage from a city of 3 million people and that serious disturbance of marine ecosystems has occurred.
The Tasmanian government imposed a ‘nitrogen cap’ to limit the amount of nitrogen released from salmon farms to D’Entrecasteaux Channel, the Huon River and Port Esperance. The permitted nitrogen loading is roughly equivalent to that from a human population of 3 million. Also, the nitrogen “cap” doesn’t account for the toxicity of ammonia which depends on the pH, temperature and salinity of the water.
Mr Flanagan told the ABC Late Night Live host Phillip Adams that the salmon producers transport large volumes of fresh water to keep the fish cool. That would also alter the water chemistry within the fish pens to maintain growth of the fish and reduce the risk of stress due to lack of dissolved oxygen. However, adding fresh water would tend to increase the risk of ammonia toxicity and the benefit of cooling would be unlikely to extend to the marine ecosystem outside of the salmon pens.
Tasmanian farmed salmon product packaging gives the impression that all is ‘clean and green’ but, like Mr Flanagan, I’m not convinced.

One Comment

  1. Alan Stevenson

    Alan Stevenson

    May 2, 2021 at 11:16 am

    It’s great to hear from Max again after a prolonged lull. As usual, his comments reflect a lot of thought and an understanding of complex environmental situations. As an outsider, I was wondering if the toxicity situation could be resolved if the salmon were to be raised in an enclosed environment like a dam or small lake. The effluent could then be used to improve the surrounding area; there would be few, if any predators; any unwanted or dangerous side-effects could be treated in situ. Surely it can’t be all that different from farming prawns.

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