DISTRIBUTION AND SETTLING OF JAPANESE ANCHOVY (ENGRAULIS-JAPONICUS) EGGS AT THE SPAWNING GROUND OFF CHANGJIANG RIVER IN THE EAST CHINA SEA

Spatial patterns in the distribution and abundance of Japanese anchovy , Engraulis japonicus, eggs were studied from net surveys in the East China Sea in May 1991. Egg abundance was >5 x 10(3) eggs (100 m(3))(-1 ) in the area off Changjiang River, where a large spawning ground was developed. The vertical distribution of living eggs showed a maximum c oncentration at the surface (40700 eggs (100 m(3))(-1)) and rapidly de creased to similar to 5000 eggs (100 m(3))(-1) at 14 m. Newly spawned eggs (stage I) were found throughout the water column but were most ab undant near surface. Some eggs were morphologically identified as dead owing to their abnormal development and physical damage. In contrast to living eggs, no dead eggs were found at the surface and the concent rations were low to 21 m depth (40-64 eggs (100 m(3))(-1)). The concen tration increased markedly with increasing depth, reaching a maximum o f 634 eggs (100 m(3))(-1) near the bottom (35 m). Dead eggs accounted for less than 0.3% of the total caught within 7 m of the surface and i ncreased exponentially to 12% near the bottom. The settling loss of de ad anchovy eggs also was studied by employing sediment traps at the sp awning ground. The downward flux of settling eggs was low (304-405 egg s m(-2) day(-1)) at 15 and 20 m depths, but rapidly increased with inc reasing depth, reaching a maximum of 1622 eggs m(-2) day(-1) at 35 m ( 5 m above bottom). By comparing the egg flux at 20 m with the living e ggs abundance in the upper 20 m, the settling loss of eggs was calcula ted as about 0.098 day(-1). This probably represents the natural morta lity of anchovy eggs caused by genetic abnormalities and incomplete fe rtilization.