Coastal water temperature difference, a potential predictor of glass eel recruitment in Anguilla japonica during non-meander periods of the Kuroshio

Abstract

Predictability of glass eel recruitment of Japanese eel (Anguilla japonica) was examined with a simple indicator constructed using coastal water temperature under the influence of the western boundary current, the Kuroshio. The 1971–2014 glass eel catch from an estuary, Lake Hamana, Japan, was compared with the mean water temperature difference (WTD) between two coastal sites, Shirahama and Lake Hamana, during the glass eel fishing season. The directions of interannual change (i.e., increase/decrease) in the glass eel catch and WTD fully synchronized for 12 consecutive years (1995–2006), and these variables were positively correlated (r = 0.68, p = 0.0150). The WTD was correlated with the southernmost latitude of the Kuroshio path (r = 0.40, p = 0.0068) in the fishing season of the study period (1971–2014); therefore, the WTD appeared to reflect the path fluctuations of the Kuroshio and the warm water intrusions from this western boundary current. The proportion of matching directions between the interannual changes in the glass eel catch and WTD was 0.71 for the non-meander (nearshore) path years (significantly higher than 0.5, the expected proportion of matching signs due to chance; χ2= 2.88 , p = 0.0448), whereas it was 0.46 for the meander (offshore) path years (χ2= 0.15 , p = 0.6526). Thus, the WTD tends to interannually increase/decrease with the estuarine recruitment of A. japonica glass eels when the Kuroshio flows with non-meander paths. This environment-recruitment relationship (western boundary current-recruitment link) in the Japanese eel demonstrates the importance of continuous environmental monitoring of coastal waters.