Abstract
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.
Highlights
The striped marlin Kajikia audax (Philippi, 1887), the skipjack tuna Katsuwonus pelamis (Linnaeus, 1758) and the yellowfin tuna Thunnus albacares (Bonnaterre, 1788) are pelagic fishes widely distributed in the oceans (Smith, Brown, 2002) and are the most important fishing sources for local and international fishing fleets in Ecuador (Schaefer et al, 2009; Martinez-Ortiz et al, 2015; Tanabe et al, 2017)
Isotope analysis allowed the identification of the trophic width and overlap between Auxis spp., K. pelamis, T. albacares, and K. audax
The δ13C values suggest that K. audax has a different trophic strategy, probably consuming prey from a trophic chain based in high productivity areas, while Auxis spp. may be moving to low productivity areas and consuming different prey sources
Summary
The striped marlin Kajikia audax (Philippi, 1887), the skipjack tuna Katsuwonus pelamis (Linnaeus, 1758) and the yellowfin tuna Thunnus albacares (Bonnaterre, 1788) are pelagic fishes widely distributed in the oceans (Smith, Brown, 2002) and are the most important fishing sources for local and international fishing fleets in Ecuador (Schaefer et al, 2009; Martinez-Ortiz et al, 2015; Tanabe et al, 2017). The pelagic fishes K. audax, T. albacares, K. pelamis and Auxis spp. are important components in the ecosystem and facilitate energy transfer between low and top trophic levels because they are preyed on by sharks, fishes, seabirds, and marine mammals (Wang et al, 2003; Arizmendi-Rodríguez et al, 2006; Galván-Magaña et al, 2013; Rosas-Luis et al, 2016; Diop et al, 2018) They are active predators of fishes, cephalopods, and crustaceans (Alverson, 1963; Loor-Andrade et al, 2017; Rosas-Luis et al, 2017; Varela et al, 2017). These species are efficient transfers of biomass to other areas and water depths since they are fast-moving species that perform horizontal and vertical movements (Holland et al, 1990)
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