Clay particles could help fish farmers tackle deadly plankton blooms

Method known as clay spraying may help end plankton blooms, fish deaths

Dumping clay into the water when there is a plankton bloom, like last month, when 600 tonnes of fish died, could be a lifeline for fish farmers in Singapore.

Clay flocculation, also known as clay spraying, involves the spraying of clay particles into the water so that they can bind to the plankton before they clump together and sink to the sea floor.

It is among the solutions the Fish Farmers Association of Singapore will be proposing to the Agri-Food and Veterinary Authority (AVA) next month.

Mr Timothy Ng, the association's president, speaking to The Straits Times after a members' meeting on Tuesday, said the group will send a proposalthat will also include an appeal for financial help to restart their businesses.

Fish farmers here are still reeling from the deadly plankton bloom last month and early this month, which wiped out almost all their fish stocks overnight.

While coastal farms in Changi were the most badly hit, those in Lim Chu Kang and Pulau Ubin were not spared either.

Mr Ng said he does not know of any farmer here who has tried clay spraying. "We hope we can go on study trips to find out more about it. Currently, what we know is from the Internet," he said. "We don't want to take the risk and restart our business unless there is some confidence that these methods can work."

According to the United States Environmental Protection Agency's website, clay has been effectively used during "red tides" in South Korea and Japan. Red tides refer to algae blooms that turn the water red.

Experts, however, said more research needs to be done to study the effectiveness of clay in the Singapore context, and the impact it could have on marine life.

The plankton said to be the cause of the recent fish kills here is "much smaller" than the one found in the algae blooms in South Korea, said Professor Gustaaf Hallegraeff from the Institute for Marine and Antarctic Studies at the University of Tasmania.

Some plankton blooms contain deadly algae which take up oxygen in the water and suffocate marine life.

"It would be difficult to quantitatively remove these minute cells by clay flocculation," he said. It should be used only as an "emergency procedure" as settling clay could have "adverse impacts" on bottom-dwelling marine life.

Associate Professor Federico Lauro from the Asian School of the Environment at the Nanyang Technological University said: "If they are planning to use natural clays, the problem is that algae is precipitated but not killed. Some of the algae can escape and still be deadly to the fish."

Another solution proposed by the farmers is to tow floating fish farms to areas with better water conditions, such as Pulau Tekong. The use of bags to store fish, and a closed containment system are two other proposed methods.

AVA said yesterday it is working with the fish farmers to recover from recent plankton blooms, and build up resilience against similar incidents in the future.

"This includes putting in place robust contingency plans and conducting contingency exercises." AVA added that it will help the farmers learn from those who have installed resilient systems.

"Farmers can also tap on AVA's Agriculture Productivity Fund to purchase relevant equipment to enhance their resilience. Beyond these, we are also exploring further assistance for affected farms to restart their operations."

Last Friday, AVA met with about 10 fish farmers to discuss how they can move forward, said Mr Ng. It also shared with them possible improvements to contingency plans, such as having a colour-coded system to warn them of adverse water conditions.

Said Mr Ng: "We have to spend six months to a year growing new fish fry, with no income in between."

kcarolyn@sph.com.sg