1Faculty of Bioresources, Mie University, Tsu, Mie, 514-8507, 2JAMARC of Fisheries Research Agency, Yokohama, Kanagawa, 220-6115, 3Seikai National Fisheries Research Institute, Fisheries Research Agency, Nagasaki, 851-2213 Japan
Diel variability in the catch composition of a bottom trawl survey in the East China Sea is analyzed using the results of sixteen (eight in the day and eight at night) operations. Of several fishes including the Japanese common flying squid, the average catch weight and number were larger at night. Of several fishes including swordtip squid and yellow sea bream, they were larger during the day. A small difference in average size between day and night was observed in Thamnaconus hypargyreus, Japanese horse mackerel, and male and female of Ovalipes punctatus. The average number of species caught was larger at night. It is also suggested that, by operating in both day and night, the number of species appearing in the survey catch can be increased without increasing the number of operations.