Stable‐isotope analysis reveals sources of organic matter and ontogenic feeding shifts of a mangrove‐dependent predator species, New Granada sea catfish, Ariopsis canteri

To gain a better understanding on the trophic ecology of New Granada sea catfish, Ariopsis canteri, and their linkage to mangroves, nitrogen and stable carbon isotopes (δ15N and δ13C), as well as Bayesian mixing models, were used to explore trophic dynamics and potential ontogenic feeding shifts across different size classes: class I (8–20 cm), class II (21–32 cm) and class III (>32 cm). The study area was the estuary of the Atrato River Delta, where information about fish ecology is scarce. The δ13C of size class I was lower (mean ± s.d. = −24.96 ± 0.69‰) than that of size classes II (−22.20 ± 0.90‰) and III (−22.00 ± 1.96‰). The δ15N of size class I was lower (mean ± s.d. = 8.50 ± 0.67‰) than that of size classes II (9.77 ± 0.60‰) and III (10.00 ± 0.66‰). Body size was positively and significantly correlated to δ15N and δ13C. Individuals with LT > 32 cm presented the highest estimated trophic position (3.8). Five‐source mixing models indicated that for class I, the mean estimated contribution of macroalgae was the highest (6%–57% c.i.), and for classes II and III, the mean estimated contribution of macrophytes was the highest (3%–53% c.i. and 4%–53% c.i., respectively). Ontogenetic feeding shifts of A. canteri were confirmed evidencing decreasing intraspecific competition between small and large individuals. Results suggest that mangroves are a nursery and feeding ground habitat for this species and that mangroves support A. canteri mainly due to the substrate/habitat that supports sources in the food webs. These results can be used in ecosystem‐based fishery management focused on the protection of extensive mangrove areas in the southern Caribbean Sea.