02 January 2010

'Dead fish zone' hits Pulau Ubin

Today it was reported that the 50 fish farms around Pulau Ubin have lost fish, with some losing as much as 60% of their stocks.
Fish farm off Pasir RisRecent comments on Facebook suggest the massive dead fish situation has also extended to Changi.

What is causing the fish deaths?

According to the reports, the Agri-Food and Veterinary Authority (AVA) attributes it to 'plankton blooms'. AVA's reported explanation: "plankton blooms occur when one species of these drifting marine organisms predominates over others and multiplies quickly. The rapid increase in the number of these organisms drains the sea water of oxygen and deprives fish and other animals of it. The current bloom was triggered by fickle weather, higher concentrations of nutrients in the sea water and poor water exchange between the high and low tides."

The farmers had thought at first that the plankton bloom was the result of the Serangoon Tidal Gates' regulation of the water levels for the upcoming Serangoon Reservoir near the fish farms. But the Public Utilities Board has since clarified that the tidal gates have not begun operations.

What are the fish farms doing about this?

When they first noticed the fish deaths, some measures taken by the fish farms included pumping seawater from greater depths to the surface to aerate the water there, and lowering nets so the fish swim in the more oxygen-rich water lying deeper in the ocean.

In a last-ditch attempt, some farmers "released their fish into the sea to raise their chances of survival, but this did not seem to work either".

Some fish farms are moving their more expensive fish such as the mouse garoupa - which can fetch up to $105 per kg - to an enclosed tank with controlled salinity and temperature. Each tank costs about $10,000 each.

The fish farms are also asking for government help.
  • To give affected fish farmers grants to invest in more enclosed tanks so that the farmers can be protected against future fluctuations in water conditions.
  • To find new ways to farm fish instead of relying on open-sea farming.
  • Help with their capital losses and information on when it is safe to start farming again. Some fish farmers say they do not have enough capital to rebuild their stocks, and that even if they did, they do not know when it would be safe to start rearing fish again.
How big is the fish farming business in Singapore?

The AVA estimates that the 13 affected farms supply 0.5% of the fish consumed here each year. The marine aquaculture industry, comprising 106 licensed coastal floating netcage fish farms in all, occupies 85.5ha of coastal water. It produced some 3,235 tonnes of fish valued at $11.40 million in 2008, accounting for 4 to 5% of the fish consumed here annually.

Some fish farmers are describing their losses as the biggest in the 10 years they have been in business.

From these latest articles about the fish deaths

Some thoughts

If hypoxic conditions (low- or no-oxygen water) start at the sea bottom where micro-organisms accumulate and are decaying, then it doesn't seem like the best solutions are to bring up bottom water into fish cages or to lower the cages into the sea bottom. Wouldn't this worsen the situation instead?

Do the fish farms themselves contribute to 'dead fish zones'?

The fundamental cause of such zones is eutrophication. Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem that results in a 'bloom' of micro-organisms, which then die and decay. The water then becomes cloudy and tinged green, yellow, brown, or red.

Fish farms contribute to 'chemical nutrients' when food, antibiotics and other supplements are give to the fishes in open cages in the sea. And fishes in open cages produce wastes which stream into the surrounding water.

One study found that "nutrient emissions from aquaculture contribute to eutrophication, which is currently changing the Baltic Sea ecosystem. Current nutrient emissions related to rainbow trout aquaculture in Finland, coming directly from aquaculture and indirectly trough waste management, contain 70% of the original nutrients in feed."
"Fish consumption and eutrophication – nutrient emissions from rainbow trout aquaculture" by Eero Asmala, Laura Saikku, University of Helsinki, Helsinki, Finland

Another study reports "Some forms of aquaculture cause significant impact on the natural environment and hence there is considered to be a need to control aquaculture developments. Predicting the potential for eutrophication requires the quantification of the amount of soluble waste being released from fish farms; use of numerical models to predict eutrophication in terms of enhanced phytoplankton biomass; establishment of environmental quality objectives and standards."
Managing eutrophication associated with aquaculture development
R. J. Gowen Aquatic Sciences Research Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast, Northern Ireland

I wonder if these aspects are being studied and considered in the decision to ramp up aquaculture in Singapore?

Sadly, it is not just fish farm fishes that are dying but also wild fishes.

Perhaps instead of focusing on rearing fish in tanks out of the sea (and dumping fish waste and dead fish into the waters), fish farms ought to better understand the ecosystems that their business relies on? And try to work with nature to ensure clean waters and good fish output. This seems a more sustainable approach to aquaculture in Singapore.

See also KwokCK's excellent explanation of eutrophication on his Water Quality in Singapore blog with reference to the fish deaths at Pasir Ris.

More links to aquaculture issues

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