LAUSR

Numerous riverine ecosystems in Iran are currently suffering due to various human activities, which are directly affecting the physico-chemical conditions of running waters and influencing the aquatic biota. In this study, we chose the cold-water streams of the Southern Caspian Sea Basin in Iran to analyse human pressures and develop a multi-metric fish index for the cold-water streams dominated by brown trout, Salmo trutta in this Basin. To do this, the fish and environmental data were sampled in 67 medium sized streams in the Caspian Mountains. In total, nine fish metrics were calculated. Moreover, 27 criteria describing major anthropogenic pressures for the entire sampling area were used to generate a regional pressure index that accounted for potential effects of multiple human pressures. For the index development, we first defined reference sites and then quantified differences of fish metrics between the reference and impacted sites. The multiple linear regressions were used for describing metric responses to natural environmental differences in the absence of any human pressures. Finally, by testing the ability of each metric for discrimination of impacted and reference sites as well as their sensitivity to a gradient of regional pressure index, the metrics density of brown trout and biomass of sub-adult brown trout explained human pressures best. Our multi-metric fish index performed well in discriminating between reference and impacted sites, giving a significant negative linear response to a gradient of regional pressure index. In general, the development of such an index offers an opportunity to enhance national bio-monitoring programmes in Iran.