Abundance and distributional changes of Japanese sardine eggs around Kyusyu, Japan, from 1979 to 1995

摘要

Egg abundance and distributional changes of the Japanese sardine Sardinops melanostictits were studied in the waters around Kyushu. Japan, from 1979 to 1995. A total 13138 tows was undertaken for collecting eggs by six prefectural experimental stations and the Scikai National Fisheries Research Institute, using 45 cm diameter plankton nets. The egg abundance was calculated for each 30 min X 30 min square and grouped into three large areas from north to south (Areas I (north of 34 deg N). II (34 degapprox 31 deg 30 deg N), III (south of 31 deg 30 min N)). The total number of sardine eggs considerably fluctuated from 47 X 10~(12) in 1995 to 2873 X 10~(-2) in 1987. The fluctuation mainly occurred in Area III. The egg abundance of this area drastically decreased from 1991. and was only 0.3 X 10~(12) in 1995. The spawning month showed secular change. In Area I, spawning occurred mainly in March in 1979 and 1980, April in 1981-1983, and May in 1984-1987. Spawning after 1988 has occurred in March and April. The main spawning grounds were located in Area I and Area II in 1979 and 1980. After 1981. the main spawning grounds gradually shifted to the south, and in 1987 most of the spawning occurred in Area III. The spawning temperature changed with the shift of the spawning area. In 1979. eggs were spawned in 13-19 deg C, although spawning occurred at the 21 deg C level in 1987. After 1991. the spawning temperature returned to 14-19 deg C.