Mercury is a trace element that is potentially dangerous due its high toxicity and tendency to bioaccumulate in organisms. Currently, high mercury concentrations are seen in the environment especially due climate changes. Studies regarding mercury bioavailability in the southwestern Atlantic Ocean using tuna and tuna-like species are rare. The aim of the present study was to use tuna and tuna-like species ( Thunnus atlanticus , Thunnus albacares , Katsuwonus pelamis , Euthynnus alletteratus , Coryphaena hippurus and Sarda sarda ) as indicators of the availability of total mercury (THg) in oceanic food webs of the southwestern Atlantic Ocean. THg concentrations varied significantly among species for both muscle and liver (Kruskal–Wallis test; H 5,130  = 52.7; p  < 0.05; H 5,130  = 50.1; p  < 0.05, respectively). The lowest concentrations were found in C. hippurus (0.008 mg kg −1 wet weight in the muscle and 0.003 mg kg −1 wet weight in the liver), and the highest concentrations were reported in the muscle of T. atlanticus (1.3 mg kg −1 wet weight) and in the liver of S. sarda (2.5 mg kg −1 wet weight). The continued monitoring of tuna and tuna-like species is necessary to assist in their conservation since tuna can be sentinels of mercury pollution.