National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Hatsukaichi, Hiroshima 739-0452, Japan
Egg production of Japanese anchovy, Engraulis japonicus, in the Seto Inland Sea was estimated based on extensive egg census data from 1980 to 2005. The fluctuations in temporal and spatial distribution of anchovy egg production were analyzed to understand trends of adult stock and the relationship between egg production and sea surface temperature. From 1980 to 2005, the annual egg production in the Seto Inland Sea fluctuated between 153 trillion in 1993 and 1,146 trillion in 2002. Spawning occurred mainly for 5 months from May to September. Annual egg production was the largest in Iyo-Nada. Density of annual egg production was the largest in Osaka Bay. Anchovy eggs were detected in the SST range from 7.9 to 31.7°C, and more concentrated from 16.0 to 28.9°C. Mean SST from May to September tended to be lower than the 26-year mean from 1986 to 1993 and higher than in 1994 and after. The fluctuation of total egg production from May to September showed similar trends as that of the mean SST except for 1997 and 1998.