Niche Differentiation Among Large Pelagic Fishes in the Southwest Atlantic Revealed by Stable Isotope Analysis

Abstract

Understanding the trophic ecology of large pelagic fishes is essential to assess their ecological role in marine ecosystems and to develop effective conservation strategies. In the present study, we aimed to provide new information on the trophic ecology of eight large pelagic fish species ( Thunnus atlanticus (blackfin tuna), Thunnus albacares (yellowfin tuna), Katsuwonus pelamis (skipjack tuna), Sarda sarda (Atlantic bonito), Euthynnus alletteratus (little tunny ) , Coryphaena hippurus (dolphinfish), Istiophorus albicans (Atlantic sailfish), and Kajikia albida (white marlin)) using carbon and nitrogen stable isotope analysis. The isotopic data were used to determine the foraging range and trophic position of the species and to assess the isotopic niche widths and resource partitioning between them. Pelagic fish samples ( N = 163) were acquired from the Cabo Frio commercial fleet, Rio de Janeiro, Brazil, between February 2009 and January 2010. We found significant differences in both δ 13 C and δ 15 N values among the species. S. sarda appears to feed at higher trophic levels and shows isotopic niche segregation with the species analyzed. However, there was a high degree of niche overlap between the other species, with the exception of the genus Thunnus . The isotopic niche width varied among species, with C. hippurus and E. alletteratus showing the widest niches, while S. sarda had the narrowest. These results highlight relevant aspects of the trophic dynamics of species of high commercial value in a region that has not been previously studied. The information contained here can serve as a basis for future conservation and management strategies for these species in the southwest Atlantic.

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