Migration of Japanese temperate bass Lateolabrax japonicus juveniles within the Chikugo River estuary revealed by δ13C analysis

Abstract

With conventional techniques it is difficult to evaluate the nursery value for migratory juveniles of Japanese temperate bass Lateolabrax japonicus within the Chikugo River estuary in Japan, especially in lower salinity areas where highly abundant prey organisms are distributed. In the present study stable carbon isotope ratios (δ13C) were used as a migration tracer within the estuary. Based on preparatory information from diet-switch experiments and field observations of prey organisms, the ranges on which tissue δ13C values of juveniles should converge (convergence range) were determined in lower and higher salinity areas (LSA salinity < 10, HSA salinity > 10). For early juveniles, muscle δ13C values were analyzed and ages were determined by otolith increment counts. For more developed juveniles δ13C values were analyzed in muscle and liver, whose half-life values were 11.4 and 2.9 d, respectively. Temporal patterns of migration were estimated by comparing δ13C values in muscle and liver with the convergence ranges of both LSA and HSA. Early juveniles aggregated around the river mouth in March 2003 and the majority gradually ascended the river to LSA by April. Most of them stayed in LSA until August, while some began to expand their home ranges to HSA after July. In addition, it is suggested that the timing of ascent influenced the early growth of juveniles. Consequently, the potential importance of LSA was demonstrated during the first growth season of Japanese temperate bass in the estuary. © Inter-Research 2008.