Tonnes of fish killed as red tide spreads

Red tide left two tonnes of fish dead off Tai O, western Lantau, as the algal bloom spread into southern Hong Kong waters in the past week.

The algae in this case is not toxic, fisheries officials say, but hot weather has sped up its decomposition, reducing oxygen in the waters off the fishing village. That causes the fish to suffocate.

The Agriculture, Fisheries and Conservation Department said the red tide, a natural phenomenon, had this time been caused by an algae called Protopolykrikos distortus, which was also recorded in Hong Kong waters from 2005 to 2007 and in 2009 but did not kill any fish.

A departmental spokeswoman said the summer heat and Tai O's geography had caused the red tide to spread. 'The recent hot weather has raised water temperatures and sped up decomposition of algae,' she said. 'The decomposition then consumes all the oxygen in the water.

'Tai O waters are shallow and water flow is static.' This caused the oxygen depletion, she said.

On receiving complaints from residents about the smell of the dead fish, the Marine and Food and Environmental Hygiene departments had begun clearing them from Tai O on Monday. In two days, they collected 1,870kg of dead fish in the sea and on the shore.

Ho Pui-han, a Tai O resident, said the odour had gone yesterday after the fish were removed.

The fisheries department first received red tide reports on August 15.

Now the algae is hitting southern and southwestern waters including 22 beaches in Tsuen Wan, Tuen Mun, Cheung Chau, Lantau Island, Repulse Bay, Shek O and waters near Lamma Island. Red flags have been hoisted at all of the beaches.

It also spread to waters off Cyberport in Pok Fu Lam yesterday, the department confirmed.

In Tuen Mun, the supply of sea water for toilet flushing was for a time suspended and replaced with fresh water.

The red tide has spread to three other fish culture zones: Ma Wan, between Lantau Island and Tsing Yi Island; and Lo Tik Wan and Sok Kwu Wan on Lamma.

Pang Wah-kan, who leads a help group for fish farmers in Cheung Sha Wan and Lamma, said he had reports of dozens of dead fish in Cheung Sha Wan, Kowloon, in the past few days. 'For the time being we will stop feeding the fish for one to two weeks because without the food the fish will not swim up to the water surface, where algae is floating,' Pang said.

Lee Choi-wah, who leads an association of seafood businesses, said some fish deaths had also been reported in Lamma and he understood that fishermen would pump oxygen into the water to protect the fish.

The department said it had liaised with the Guangdong Provincial Oceanic and Fishery Administration and exchanged information.

22

Number of beaches hit, including on the south of Hong Kong Island. Red flags have been hoisted.