Stable nitrogen and carbon isotope ratios as migration tracers of a landlocked goby, Rhinogobius sp. (the orange form), in the Lake Biwa water system

Abstract

Fluvial–lacustrine migrations of a landlocked goby, Rhinogobius sp. (the orange form) in the Lake Biwa water system were traced using stable nitrogen and carbon isotope ratios. The δ15N values of Rhinogobius sp. individuals in the lake were significantly higher than those of large individuals in a tributary river (≥1+ age) without overlap of the range, although there was little difference in the δ13C values between these two locations. Because these values reflected those of the corresponding prey organisms in either location, it was revealed that none of the large individuals had migrated from one location to the other. The δ15N values of the small individuals in the tributary river (0+ age) were too high to be fluvial residents. This result indicated that all of the small individuals studied had spent their larval periods in the lake, and that immigrant individuals can be distinguishable by measuring the δ15N values retaining the effect of foraging in the alternate location. We conclude that the δ15N value works as a useful tracer to clarify the fluvial–lacustrine migration pattern of the fish.