Age-based δ15N and δ13C values of otolith organic matter reveal trophic ecology in marine fishes

Fish inhabiting similar environments face space and resource constraints, develop diverse feeding strategies, and adjust their trophic niches during ontogeny to reduce competition. To investigate this process, we reconstructed the trophic trajectory of five species of the family Sciaenidae by analyzing delta 13C and delta 15N values in otolith organic matter along the growth axis of the otolith. We developed and optimized the approach by aligning isotope values with an age range estimated using growth ring counts and three-dimensional scanning of otolith morphology during organic matter extraction. delta 13C values indicated habitat shifts, and delta 15N values provided insights into trophic level changes, showing that sciaenids use benthic resources throughout their lifespan and may move closer to estuarine environments at approximately an age range from 1.5 to 3 yr old. During the early life stages, their diet consists of herbivores. As they grow, competition among age groups and species appears to be minimized.