CHARACTERISTICS OF BLUE TIDE UPWELLING IN SANBANZE SHALLOWS AT TOKYO BAY AND EXAMINATION OF ITS IMPACTS ON HARD CLAM

Abstract

 In order to clarify the dynamics of blue tides in the Sanbanze shallow water area at the head of Tokyo Bay, water quality measurements and interval photographing were performed in summer and autumn of 2017 and 2018. A couple of blue tides were observed in the Sanbanze fishing ground, having a tendency to occur first in the Funabashi navigation channel and off-Makuhari, and then in the Ichikawa navigation channel and off-Urayasu. This time lag was considered to be due to immediate upwellings of anoxic waters containing sulfide in the bottom layer of the Funabashi channel. A series of laboratory experiments was conducted to examine the influence of marine waters, including blue tides, on hard clams, one of the major fishery products in this fishing ground. Hard clams were found to die within 2 days at a high water temperature of 35 °C. When exposed to anoxic water with hydrogen sulfide, discoloration of their shells were observed.