Stable isotope analysis reveals partitioning in prey use by Kajikia audax (Istiophoridae), Thunnus albacares, Katsuwonus pelamis, and Auxis spp. (Scombridae) in the Eastern Tropical Pacific of Ecuador

Kajikia audax, Thunnus albacares, Katsuwonus pelamis, and Auxis spp. occupy high and middle-level trophic positions in the food web. They represent important sources for fisheries in Ecuador. Despite their ecological and economic importance, studies on pelagic species in Ecuador are scarce. This study uses stable isotope analysis to assess the trophic ecology of these species, and to determine the contribution of prey to the predator tissue. Isotope data was used to test the hypothesis that medium-sized pelagic fish species have higher delta N-15 values than those of the prey they consumed, and that there is no overlap between their delta C-13 and delta N-15 values. Results showed higher delta N-15 values for K. audax, followed by T. albacares, Auxis spp. and K. pelamis, which indicates that the highest position in this food web is occupied by K. audax. The stable isotope Bayesian ellipses demonstrated that on a long time-scale, these species do not compete for food sources. Moreover, delta N-15 values were different between species and they decreased with a decrease in predator size.

Automated summary

The study used stable isotope analysis to evaluate the trophic ecology of four pelagic fish species in Ecuador, with results showing K. audax occupying the highest position in the food web. On a long-term scale, these species do not compete for food sources, and δN-15 values decrease with a decrease in predator size.