Since the early 2000s, in the Hiuchi-nada area in the center of the Seto Inland Sea, the catch of whitebait and kaeri (fry) of Japanese anchovies, which are used for dried young sardines and dried sardines, has declined sharply. .
A joint research team consisting of the Japan Fisheries Research and Education Agency, Kagawa Prefecture, Ehime University, and Hiroshima University conducted field surveys and breeding experiments to determine the cause of the slump in catches of anchovies in Hiuchi-nada. .
First, in recent years, zooplankton (copepods), which is the main food for anchovies, has decreased significantly from spring to early summer, which includes the peak spawning season of anchovies.Next, it was found that female anchovies in recent years have become thin, probably due to the decrease in zooplankton.Breeding experiments have shown that the eggs laid by lean females are smaller than those laid by fat females, and that the larvae that are produced also have lower growth rates.In fact, a comparison of the total number of eggs laid and the number of larval catches from 1994 to 2019 shows that although the total number of eggs laid has increased in recent years, the number of larval catches has decreased sharply since the 2000s. Admitted.
In other words, it is inferred that female anchovies become thin and lay eggs of poor quality due to the decrease in food plankton, and the survival of larvae in the early stages of development is markedly reduced.It was thought that the recent poor catch of whitebait and Japanese kaeri in Hiuchi-nada was the result of these complex factors.
In recent years, it has been pointed out that the concentration of nutrients in the Seto Inland Sea has decreased (oligotrophication) and that the water temperature has increased, and these are thought to be related to the decrease in plankton that feeds on anchovies.The results of this research are expected to provide a stepping stone to dramatically advance understanding of the complex causal relationship between oligotrophic changes in forage plankton generation and sluggish fisheries production in the Seto Inland Sea.
Article information XNUMX:[Progress in Oceanography] Bottom-up processes drive reproductive success of Japanese anchovy in anoligotrophic sea: A case study in the central Seto Inland Sea, Japan
Paper information XNUMX:[Fisheries Oceanography] Temporal variations in hatch date and early survival of Japanese anchovy (Engraulis japonicus) in response to environmental factors in the central Seto Inland Sea, Japan