Mass mortality event of aquaculture oysters caused by high precipitation in Setiu Lagoon, Peninsular Malaysia, during the wet season

Abstract

Mass oyster mortality occurred at an oyster farm in the Setiu Lagoon on the east coast of Peninsular Malaysia in December 2023. According to interviews with aquaculture farmers, heavy rains that occurred from 20 November to early December caused flooding in the surrounding area, leaving it exposed to low-salinity water for a long period. Mass mortality occurred at oyster farms in early December, with farmers estimating that the dead oysters had a shell length of 1–5 cm and mortality rate of over 90%, and that approximately 50,000 oysters had died. An analysis of meteorological data indicated that a monthly rainfall value of more than 1200 mm/month, which is more than double the normal amount, was observed in November in the same region. During the same period, the seawater temperature in the South China Sea was 1°C higher than normal, and the northeast monsoon caused winds from the northeast to transport moist air to the eastern coast of Peninsular Malaysia, causing heavy rain. Currently, only one waterway, approximately 200 m wide, connects the lagoon to the sea. Until approximately 2012, two waterways were connected to the sea. We concluded that by increasing the number of channels to two, the decrease in salinity in the lagoon during the rainy season could be reduced by enhancing phytoplankton occurrence.

Keywords

• mass mortality
• oyster farming
• high precipitation
• setiu lagoon
• peninsular malaysia