In response to the multiple red tide sighting reports in Hong Kong waters received recently, an inter-departmental red tide working group today (August 3) reported that sample analysis results showed that all red tides were caused by Polykrikos geminatum, which is non-toxic and was not commonly found in Hong Kong waters .

     A spokesman for the working group said that red tide is a natural phenomenon. Various factors, such as nutrient level, water temperature, salinity, current, water stratification may contribute to red tide formation. It is difficult to isolate a single cause. In light of the wide extent of the red tides, the situation may last for several days. As the weather and hydrological conditions change, the red tides will naturally dissipate when the number and density of algae in the water decreases.

     From July 30 to present, the red tides mainly appear in the western and south-western waters of Hong Kong. Among the red tides sighted, six of them were spotted at beaches in Tuen Mun district, six were spotted at beaches in Tsuen Wan district, one was spotted at a beach on Lantau Island; ten were spotted at the western waters of Hong Kong (Tai O, Tung Chung, Tsuen Wan, etc); three were spotted at Victoria Harbour (near Tsim Sha Tsui, Wan Chai and Tai Kok Tsui); while two were spotted in the waters off Castle Peak Bay and Cyberport. The Agriculture, Fisheries and Conservation Department (AFCD) has collected water samples from the above-mentioned areas for analysis and found that the red tides were caused by non-toxic Polykrikos geminatum.

     Staff of the AFCD also spotted red tides caused by Polykrikos geminatum at the fish culture zones of Ma Wan and Cheung Sha Wan. Both red tides still persist. No abnormality has been observed for the fish in all fish culture zones as at today. The AFCD will continue to closely follow up on the situation at fish culture zones and urge affected mariculturists to monitor the situation of their mariculture rafts and increase aeration where necessary. The AFCD will provide appropriate assistance when needed.

     The AFCD's proactive phytoplankton monitoring programme will continue monitoring red tide occurrences to minimise the impact on the local mariculture industry and the public. Staff of the AFCD will regularly collect phytoplankton samples at fish culture zones and five offshore stations to detect the presence of harmful algal bloom and red tides. Sampling frequency would be stepped up when harmful algal species or abnormal phytoplankton population was detected.

     When spotting a red tide, members of the public may note the location, colour of the seawater, extent of the red tide, occurrence of dead fish and any other abnormal features observed around the red tide, and report via 1823.

Ends/Tuesday, August 3, 2021
Issued at HKT 23:59

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