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Isotopic characterization of lifetime movement by two demersal fishes from the northeastern Gulf of Mexico

Julie L. Vecchio*, Jenny Ostroff, Ernst B. Peebles

*Corresponding author:

ABSTRACT: An understanding of lifetime trophic changes and ontogenetic habitat shifts is essential to the preservation of marine fish species. We used carbon and nitrogen stable isotope values recorded within the laminar structure of fish eye lenses, reflecting both diet and location over time, to compare the lifetime trends of 2 demersal mesopredators. Tilefish Lopholatilus chamaeleonticeps is known to inhabit burrows on the outer continental shelf, which results in exceptional site fidelity. Red grouper Epinephelus morio is spawned on the middle-to-outer continental shelf, moves to the inner shelf for the juvenile period, and returns offshore upon sexual maturity. Both species inhabit the eastern Gulf of Mexico, a region with distinctive offshore-inshore gradient in background δ13C values. Within individual tilefish (n = 36), sequences of δ13C values and δ15N values had strong, positive correlations with eye-lens diameter, and strong correlations between the 2 isotopes (mean Spearman r = 0.86), reflecting trophic position increase with growth and little lifetime movement. In red grouper, (n = 30), δ15N value positively correlated with eye-lens diameter, but correlations between δ15N values and δ13C values were weak (mean Spearman r = 0.29), suggesting cross-shelf ontogenetic movements. Linear mixed model results indicated strong relationships between δ15N values and δ13C values in tilefish eye lenses but no convergence in the red grouper model. Collectively, these results are consistent with previously established differences in the life histories of the 2 species, demonstrating the potential utility of eye-lens isotope records, particularly for investigating the life histories of lesser-known species.