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

Abstract

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 δ15N values than those of the prey they consumed, and that there is no overlap between their δ13C and δ15N values. Results showed higher δ15N 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, δ15N values were different between species and they decreased with a decrease in predator size.

Striped marlin in their Pacific Ocean milieu: Vertical movements and habitats vary with time and place

“…Considering that striped marlin are known to rush at a sardine school near the sea surface (Hansen et al, 2020), they might use the same hunting strategy at boundary conditions, namely at the top of and in the thermocline and oxycline (Lam et al, 2015) to exploit a diverse selection of prey (Abitia-Caŕdenas et al, 1997;Shimose et al, 2010;Ortega Garcia et al, 2017). This would reduce competition with other top predators through trophic niche separation (Acosta-Pachoń and Ortega-Garcıá, 2019;Rosas-Luis et al, 2021). Application of accelerometer-coupled infra-red cameras (Cade et al, 2021), once minimization is achieved, might provide the bio-logging advances necessary to uncover the secrets of striped marlin hunting and other behavior at depths.…”