干潟におけるクルマエビ天然ポストラーバの魚類からの被食状況

抄録

Catch of kuruma prawn Penaeus japonicus in Japan has declined since the mid-1990s. It has been reported that artificial seeds released for stock enhancement are heavily predated by fish in tidal flats, but this has not been reported for natural postlarvae. Therefore, to clarify the predation pressure on natural postlarvae, the postlarvae and surrounding fish were simultaneously collected using a rake sledge net on tidal flats at three sites along the Pacific coast of central Japan during the daytime from July to December 2021. The highest density of natural postlarvae in this study(5.7 individuals/m²)was less than that recorded immediately after the release of artificial seeds, but comparable to that recorded before the mid-1990s when the catch was higher. A total of 888 individuals of 21 fish species were collected with the prawn, with a high abundance of the goby Favonigobius gymnauchen. This goby has been reported as a predator on artificial seeds and occurred during the periods when natural postlarvae were abundant. However, few postlarvae were observed in the stomach contents of these fish, except for a small specimen of crescent sweetlips Plectorhinchus cinctus. These results suggest that natural postlarvae are less vulnerable to predators than artificial seeds potentially due to behavioral difference in addition to the lower density. It is probable that the sinking behavior in the sand during daytime in abundant artificial seeds attracts predators, although natural postlarvae do not perform such behavior because of the lower developmental stage.