Horizontal distribution and abundance of red seabream (Pagrus major) in the East China Sea and Sea of Japan based on standardized catch per unit effort

Abstract

Red seabream (Pagrus major) is an important fisheries species in Japan, where it has been managed since 2025. Accurate stock assessment is necessary for rational fisheries management, and catch per unit effort (CPUE) is one of the key indexes used for this purpose. In the present study, the CPUE of red seabream in the East China Sea and Sea of Japan was standardized by incorporating seawater temperature and salinity based on fishing data obtained from bottom trawlers operating in key fishing grounds in these regions. We used data from operation reports available from 1982 to 2022, including fishing positions and efforts during each cruise and incorporated temperature and salinity data into the model from 1993. We applied a delta log-normal model for CPUE standardization and revealed an increase in this index since the early 1990s. We examined the horizontal distribution patterns of red seabream in each fishery grid that is 30 × 30 min latitude and longitude, and observed that the high-CPUE area extended northeastward from Taiwan to Japan along the shelf edge, which corresponds to the main fishing grounds covered by Japanese fleets after 2000. The probability of presence of red seabream increased drastically when water temperature at a depth of 50 m exceeded 15 °C. The reasons for the observed stock fluctuations may be a reduction in fishing pressure and warming seawater temperature.