Red tide sighting report by the inter-departmental red tide working group


     ​In response to the multiple red tide sighting reports in Hong Kong waters received over the last few days, the Inter-departmental Red Tide Working Group today (March 14) reported that sample analysis results showed that all these red tides had been caused by Noctiluca scintillans, which is non-toxic and 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. Given 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 decrease.

     From March 12 to 4.30pm today, eight red tides were spotted at Big Wave Bay Beach, Rocky Bay Beach, Middle Bay Beach, South Bay Beach, Repulse Bay Beach, Deep Water Bay Beach, Stanley Main Beach and Chung Hom Kok Beach, Hong Kong Island, respectively; while three were spotted at the Tathong Channel to Lei Yue Mun (including Junk Bay and Tung Lung Chau Fish Culture Zone), Victoria Harbour (near Hung Hom) and the Southern waters of Hong Kong (including East Lamma Channel and Sheung Sze Mun) respectively. The above-mentioned red tides still persist. 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 Noctiluca scintillans.

     No abnormality has been observed for the fish in all fish culture zones as at 4.30pm today. The AFCD will continue to closely monitor the situation of red tides in various fish culture zones and urge concerned mariculturists to pay attention to 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 will be stepped up when harmful algal species or abnormal phytoplankton population is 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 by emailing, or calling 2150 7124 during office hours.