Bull. Jpn. Soc. Fish. Oceanogr. 85(1), Page 24-32, 2021   Causal factors of interannual decrease in stomach content index (SCI) of juvenile western sand lance Ammodytes japonicus in Harima-Nada, eastern Seto Inland Sea, Japan Seiho Hashiguchi1,†, Tetsuya Nishikawa2, Kaori Uozumi2, Kazushi Furusawa1, Atsushi Mori1, Kazumasa Imao1 and Minoru Tanda2 1 Marine Biological Research Institute of Japan Co., Ltd., 4�3�16 Yutaka, Shinagawa, Tokyo, 142�0042, Japan 2 Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, 22�2 Minamifutami, Futami, Akashi, Hyogo 674�0093, Japan † E-mail: hashiguchi@mbrij.co.jp It has been pointed out that the decline of western sand lance (Ammodytes japonicus) catch in Harima-Nada is mainly caused by food shortage. In this study, the stomach content index (SCI), condition factor, and prey composition of juvenile western sand lance collected in Harima-Nada in March were investigated from 1987 to 2018. The SCI decreased significantly from 1987 to 1997 and remained less than 1% after 2001. The condition factor also decreased significantly from 2001 to 2018. Main prey items of the juvenile western sand lance were the copepods Calanus sinicusand Paracalanus sp. throughout the investigation period, and the frequency of their occurrences did not change significantly before or after 2001. On the other hand, the dissolved inorganic nitrogen concentration in January and the chlorophyll a concentration from February to March showed a significant positive correlation, and the chlorophyll a concentration and SCI also showed a positive relationship. These results suggest that poor nutrient levels were responsible for low primary production, which was in turn a potential cause of low zooplankton production. As a result, the juvenile western sand lance possibly suffered from chronic food shortage in recent years. Key words: western sand lance, condition factor, stomach content index, copepods, nutrient decrease, food shortage