Small-scale gold mining erodes fish assemblage structure in small neotropical streams

The current gold rush experienced by the Guiana shield is profoundly disturbing freshwater ecosystems. Indeed, streams act as receptors for the water that drains gold mining sites and that contain a high load of sediment and toxicants. We here investigated how gold mining activities affect the structure of fish assemblages in small forest streams in French Guiana. We selected six streams subjected to different types of gold mining impact (reference, former gold mining and currently exploited sites) to measure the impact of gold mining on downstream fish assemblages, but also to determine the resilience of fish assemblages after stopping mining activities. Although overall descriptors of the assemblage such as species richness and fish biomass were not sensitive to gold mining, the fish taxonomic composition was strongly influenced. Furthermore, we showed that the functional structure of fish assemblages was significantly affected by the mining activities favouring smaller and ubiquitous fish at the expense of bigger and habitat specialist species. Even in areas where mining activities had stopped for some time, site resilience was incomplete.