Estuarine dependency of Lates japonicus in Shimanto Estuary, Japan, inferred from otolith Sr:Ca

Understanding estuarine dependency is essential to clarify the life history of euryhaline species and propose adequate management measures. Lates japonicus is a rare fish, endemic of the estuaries and coastal waters of southeast Japan, and categorized as endangered in the Red Data Book of Japan. To reconstruct the life history of L. japonicus in Shimanto Estuary and understand estuarine residency at different ontogenetic stages, the otoliths of juveniles, young and adults captured in the estuary were analyzed using microstructure examination and elemental analysis. Otolith Sr:Ca ratio indicated that all juveniles, captured in estuarine seagrass beds, hatched within the estuary, and recruited into the seagrass beds without dispersion to coastal areas. Similarly, the otolith Sr:Ca ratio of six young and adults captured in the estuary suggested that they mainly remained in estuarine waters during all their life after recruiting in the estuary. No evidence of long-term residency in coastal waters after the juvenile stage was obtained. These results suggested that the population of L. japonicus in Shimanto Estuary relies on estuarine habitats at all life stages.

Automated summary

Understanding the estuarine dependency of the endangered Lates japonicus in Shimanto Estuary revealed a reliance on estuarine habitats at all life stages. Juveniles were found to hatch and recruit in estuarine seagrass beds without dispersing to coastal areas, while young and adult individuals mainly remained in estuarine waters after recruitment without evidence of long-term residency in coastal areas.