Impacts of mining pollution on coastal ecosystems: is fish body condition a reliable indicator?

Identifying reliable biological indicators is fundamental to efficiently assess human impacts on biodiversity and to monitor the outcomes of management actions. This study investigates whether body condition is an appropriate indicator of putative effects from iron ore mining tailings on marine fishes, focusing on the world's largest mining disaster – known as the Mariana disaster, in Brazil. Eight species were used to test the hypothesis that individuals inhabiting an area severely impacted by tailings have reduced body condition in comparison to those in control areas near (120 km) from the impact site. Contrary to our prediction, no significant difference in condition was detected between the impacted area and both near and distant controls in seven of the eight species. The results indicate that body condition, as measured by the scaled mass index, has limited applicability as indicator of impact from mining pollution on the fishes analysed. Hypotheses that could explain our findings are proposed, including nutrient provisioning from continental drainage that could indirectly influence fish condition and compensate for the deleterious effects of mining pollution. •The Doce river delta was severely impacted by the Mariana mining disaster.•The utility of fish body condition as an indicator of impact was investigated.•No effect from mining tailings on the condition of eight fish species was detected.•Body condition seems to be an ineffective indicator of impact from mining pollution.