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The Scottish Environment Protection Agency (SEPA) has published the results of a study it commissioned into the impact of fish farming on harmful algal blooms. The main conclusion from the report is that nutrients (compounds of nitrogen and phosphorus) arising from fish farming have only a small effect on the amount and growth rate of these blooms. However, this should not be a cause for concern except in a few, enriched sea-lochs.
The blooms are groups of naturally occurring species of microscopic algae that form part of plankton (plants and animals that live in the surface layers of the sea.) Some species can lead to toxins in fish and shellfish, making them unfit for humans to eat. They can also kill fish in fish farms by choking their gills or reducing the oxygen content of the water.
The three main concerns raised against the aquaculture industry are that nutrients from fish farms have:
- led to an increased occurrence of algal blooms
- encouraged toxic species to grow in place of harmless species
- made potentially toxic algae more poisonous.
In October 2000 SEPA contracted Professor Paul Tett of Napier University to carry out this review of harmful algal blooms in Scottish waters. SEPA made particular reference to waste inputs from marine fish farms in commissioning this work.
Andy Rosie, SEPA’s aquaculture specialist, said: “The review that we commissioned does not support any of these concerns. Professor Tett’s report concludes that the levels of nutrients from fish farms alone appear to be too little to have significant effects on, or be the cause of, the perceived changes in algal blooms, except perhaps in a few enriched and poorly flushed sea lochs. However, we do note his comments on the lack of data. This point has also been recognised by the Ministerial working group on aquaculture, which has identified it as a priority for action.
“Monitoring of our tidal waters has been concentrated around the industrial parts of the Forth and Clyde estuaries, but as fish farming has grown in the remote inlets of the Highlands and Islands, there is a need to increase our data set here to better inform the regulatory process which controls fish farming. This process is already underway with SEPA’s programme of audit monitoring of fish farm sites using purpose-built small survey vessels.
“Fish farming is just one of many sources of nutrients which promote algal growth. SEPA will study the report carefully and where the review suggests there may be problems, we will look at all of the relevant factors, including aquaculture, to reduce the impact on the environment. We will also continue to restrict development in areas that may be particularly sensitive to increased levels of nutrients in line with the Scottish Executive’s locational guidelines for marine fish farms.”
The main conclusions of the report are:
- Modelling studies estimate that only a few sea-loch sites are strongly enriched with nutrients to such a level that they might reach or exceed environmental quality standards.
- A lack of historic environmental data over the past 30 years has made it difficult to judge whether the perceived increase in harmful algal blooms (HABs) is real and to link these with any changes, such as the expansion in the fish farming industry.
- The data that does exist does not show conclusively that there has been a wide scale increase in the abundance of organisms responsible for harmful blooms in Scottish waters. However, the number of reported incidents of toxicity (shellfish poisoning) has increased.
- The apparent spread of shellfish poisoning on the west coast and in the Northern Isles could be due to more comprehensive monitoring or as a result of the spread of toxic strains among existing populations of algal species on which shellfish feed. However, there is no evidence that organisms that cause the poisoning are becoming more abundant either at new locations or sites where there is a history of closure of the shellfishery.
- In addition, predictive models appear to indicate that the algal production apparently caused by fish farm nutrients in Scottish coastal areas is small relative to that generated by other nutrients coming in from the Atlantic Ocean or from land runoff.
- There is still much to learn about what controls the balance of organisms within the plankton. However, some types of algal bloom (Gymnodinium mikimotoi, Phaeocystis pouchetii and toxic flagellates) do seem to be stimulated by nutrient enrichment and increases in the ratio of nitrogen and phosphorus to silicon.
- Fish farm waste has a small impact on nutrient element ratios in most Scottish waters. Similarly there is no convincing evidence that changes in nutrients from fish farms makes potentially toxic species more toxic.
For more information visit www.sepa.org.uk/aquaculture/projects/index.htm
ENDS
Contact
Stewart Argo, public relations officer – 01224 248338, 07799 477972
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