Some observations on the spawning depth of the Japanese sardine, Sardinops melanostictus, and the Japanese anchovy, Engraulis japonicus, off southern Kyushu, Japan

The vertical distribution of eggs of the Japanese sardine, Saradinops melanostictus, and the eggs of the Japanese anchovy, Engraulis japonicus, was investigated to clarify the irrespective spawning depth. Net sampling was made at the station of N35 sup (o) 55f, E130 sup (o) 29f. Vertical tows using a 45cm diameter net from 150m depth were done every two hours 15 times from 18:00, March 1 to 6:00, March 3, 1992. Horizontal tows using 60cm diameter nets with net closing apparatus were simultaneously conducted at five layers of approximately 1m, 20m, 40m, 60m and 80m, for 15 minutes, and carried out 15 times such as vertical tows. AA stage eggs (from fertilization to beginning of enlargement of perivitelline space) of Japanese sardine were mostly collected at 40m depth at 22:00, March 1, at 40m depth at 20:00 and 22:00, March 2, and at 60m depth at 0:00, March 3. This means that the spawning depth of approximately 40-60m. ’¬20m-40m. Unfertilized and disintegrating eggs were largely collected at 80m depth at 0:00, March 2 and at 40m depth at 22:00, March 2. These eggs seem to sink rapidly after spawning. Although A stage eggs (from end of AA stage to closing of blastopore) distributed from the surface to the 80m layter, a lot of eggs were collected at 20-60 depth at 4:00 and 6:00, March 2. A few AA stage eggs (from fertilization to cleavage) of Japanese anchovy were collected at 22:00, March 1 to 2:00, March 2. Many AA stage eggs were caught at 22:00, March 2 2:00, March 3. Most eggs distributed at the surface and the 20m depth layer. Therefore, it is considered that the spawning depth o f this species was approximately 0-20m. In this species, the unfertilized and disintegrating eggs as collected in Japanese sardine were not recognized. A stage eggs (to the attainment of blastoderm to 1/2 of yolk length) were mainly caught at 18:00, March 1 and from 2:00 to 6:00, March 3, A stage eggs were mostly distributed from the surface to the 20m depth layer such as AA stage eggs. This result shows that the spawning depth of these two species does not overlap, in the case where the two species coexist.