Influence of swimming form on otolith δ13C in marine fish

While temperature records are available from otolith δ18O profiles in fish, interpreting changes in otolith δ13C remains ambiguous. We compiled a global database of published otolith δ 13C values for 60 species representing 30 families of marine fishes, Species' mean otolith δ13C ranged from +0.5 to -8.6‰. Among-family variance in otolith δ13C was uniquely explained by a morphometric index for aerobic swimming activity (caudal aspect ratio, r2 = 0.61). The models that consistently explained the maximum among-species variance in otolith δ13C included caudal aspect ratio and maximum depth of occurrence. Our analysis supports the use of otolith carbon-isotope ratios to indicate metabolism (primarily active) in marine fish. This information may be applied to studies of fish feeding and related food-web structure, both past and present.