2025 Volume 89 Issue 4 Pages 227-239
To understand the ecosystem structure of Ise Bay, Japan, we analyzed fishing statistics data from 1970 to 2020 by calculating the mean trophic level (MTL) and the Shannon–Wiener biodiversity index (H′). In addition, we computed the Fishery Production Index (FPI) using biological characteristics of each fishery resource and examined the influence of primary production and water temperature on FPI. Total catch had been declining over the long term, and since around 2010, the composition of catches had changed due to a decrease in mantis shrimp Oratosquilla oratoria and conger eel Conger myriaster, and an increase in red sea bream Pagrus major and flounder Paralichthys olivaceus. While no consistent trend was observed in H′, MTL showed a long-term increase, and FPI declined after approximately 2014. Correlation analyses indicated that both MTL and FPI were influenced by reductions in total phosphorus (TP), a proxy for primary production, while MTL was also affected by rising water temperatures. In a generalized linear model with FPI as the response variable, TP values from one and three years prior emerged as significant predictors. In recent years, bottom-up effects have led to a decline in species dependent on inner bays, and changes in the food environment for large fish have also caused changes in the distribution of large fish. These results suggest that the ecosystem structure was changing and biological productivity was declining due to a shift from highly productive species to less productive species in Ise Bay.
