Past and lost influence of the Kuroshio on estuarine recruitment of Anguilla japonica glass eels

The present study aims to reveal the influence of path fluctuations of the western boundary current (Kuroshio) and other regional environmental factors on coastal recruitment of transported organisms. As a model species, we chose a catadromous eel species, Japanese eel Anguilla japonica , which is transported poleward by the Kuroshio in early life stages. We analyzed a 50-year record of A. japonica juvenile (glass eel) catch from an estuary (Lake Hamana, Japan) with regional environmental data, using multiple linear regression with stepwise variable selection. Kuroshio path indicator (fishing-season mean of sea level difference between two tide stations), year, or their interaction showed moderate to strong evidence of an effect on the natural log-transformed catch of glass eels in the regression models. Strong evidence of an interaction effect between the Kuroshio path indicator and year was also found on the natural log-transformed catch-per-unit-effort. The estuarine recruitment of A. japonica glass eels was suggested to be positively influenced by nearshore Kuroshio position, but the influence has been lost in recent decades. The present study provides statistically robust evidence of the environment–recruitment relationship (western boundary current–recruitment link) for coastal species. This finding enhances our understanding of coastal recruitment of organisms transported by western boundary currents and is potentially essential in forecasting recruitment for fisheries management and conservation. Furthermore, our findings suggest that stock decline may lead to poorer understanding of environment–recruitment relationship.