Diverse migratory histories of Japanese Trachidermus and Cottus species (Cottidae) as inferred from otolith microchemistry

The migratory histories of Japanese freshwater sculpins, one Trachidermus and four Cottus species, were studied by examining strontium (Sr) and calcium (Ca) concentrations in their otoliths using wavelength dispersive X‐ray spectrometry on an electron microprobe. The Sr : Ca ratios in the otoliths changed with salinity of the habitat. The otoliths of Cottus nozawae showed consistently low Sr : Ca ratios, with an average of 3·37 × 10 −3 from the core to the edge, suggesting a freshwater resident life cycle. In contrast, the otolith Sr : Ca ratios for Trachidermus fasciatus and Cottus kazika changed along the life history transects possibly in accordance with their migration patterns from sea to fresh water. The ratios of T. fasciatus and C. kazika averaged 5·4 × 10 −3 and 5·3 × 10 −3 respectively, in the otolith region from the core to the points 450–890 μm, and changed to the lower levels, averaging 2·0 × 10 −3 and 2·7 × 10 −3 , in the outer otolith region. These data suggest that both the species have a catadromous life cycle. The otoliths of Cottus hangiongensis had low Sr : Ca ratios in the two regions from the core to the points 15–30 μm and the points 415–582 μm to the edge, averaging 2·0 × 10 −3 and 1·9 × 10 −3 , with significantly higher ratios in the narrow area between these regions, averaging 4·6 × 10 −3 . Similar ontogenetic changes in otolith Sr : Ca ratios were found in the otoliths of Cottus amblystomopsis , suggesting their amphidromous life cycle. These findings suggest that otolith Sr : Ca ratios reflect individual life histories and that Japanese Trachidermus and Cottus species have diverse migratory histories.